tag:theconversation.com,2011:/us/topics/gut-series-32096/articlesGut series – The Conversation2016-10-20T04:29:11Ztag:theconversation.com,2011:article/654802016-10-20T04:29:11Z2016-10-20T04:29:11ZPoo transplants and probiotics – does anything work to improve the health of our gut?<figure><img src="https://images.theconversation.com/files/142432/original/image-20161020-848-1ew2pt5.jpg?ixlib=rb-1.1.0&rect=0%2C161%2C1000%2C504&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If you don't have a problem, you don't need to mess with it. </span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-428746396/stock-photo-obesity-in-teens-and-fat.html?src=ZN8MZwsUu2Xri9ONJt1SYw-2-58">Joyseulay/Shutterstock</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come.</em></p>
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<p>For more than one hundred years, we believed avoiding bugs or removing them from our system was the simplest way to improve our health. </p>
<p>But while tremendous public health advances have come from controlling dangerous pathogens, we now understand the trillions of other bacteria that live in our body – and in particular, our gut – perform a range of important functions. </p>
<p>So when, and how, should we try to manipulate these microorganisms, collectively referred to as our microbiome?</p>
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<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
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<p>What we eat satisfies the nutrient demands of our microbiome – and subsequently shapes their capacity to further contribute to our health. But the modern lifestyle, particularly diet and hygiene changes, have altered our relationship with our microbes.</p>
<p>To have a healthy microbiome, the best advice is to include natural plant foods, including fibre, in your diet. But although diet has a major role in shaping our microbiome, it’s not a precise way to re-engineer it if things have gone wrong.</p>
<p>There are two broad avenues for microbiome engineering: generic strategies that target large numbers of different microbes (bacteria) simultaneously, such as fecal transplant and antibiotics; or specific strategies that target a small group of microbes, such as probiotics. </p>
<p>Although changes in our microbiome are associated with many chronic diseases, and those changes almost certainly have some contribution to the disease, they are not necessarily the main cause. Microbiome manipulation is most useful when we know exactly how microbes are involved in particular diseases. </p>
<p>But if you don’t have a problem, you don’t need to mess with your microbiome. This is another reason why taking antibiotics when you don’t them is a bad idea.</p>
<h2>Poo transplants</h2>
<p>Fecal microbial therapy, or fecal transplants, are the transfer of a fecal sample from a healthy donor to a recipient. This can be done via nasogastric tubes (inserted into the nostril, down the throat and into the stomach) or inserted directly into the colon. </p>
<p>Fecal transplants have had spectacular success with treating <em>C. difficile</em> infections. This bacterium causes severe diarrhoea and inflammation. Recurrent infections are extraordinarily debilitating and life-threatening.</p>
<p>Trials of fecal transplants <a href="http://www.nejm.org/doi/full/10.1056/NEJMoa1205037#t=article">typically show</a> a 90% success rate in treating this condition. </p>
<p>But <em>C. difficile</em> disease is a special case. The disease has one main cause and a consequence of the infection is a greatly reduced microbiota. In the “empty” gut environment of such patients, it’s easy to introduce new organisms. The removal of one problem organism is an easy target.</p>
<p>Most conditions involving gut health – such as obesity, <a href="http://www.mayoclinic.org/diseases-conditions/inflammatory-bowel-disease/basics/definition/con-20034908">inflammatory bowel disease</a>, and <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/irritable-bowel-syndrome-ibs">irritable bowel syndrome</a>) – have more complex causes and the gut retains a high-density complex combination of bacteria. </p>
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<img alt="" src="https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142434/original/image-20161020-5007-148d2yb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Fecal transplants have raised far more questions than answers.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-75990976/stock-photo-toilet-seat-and-paper-in-nice-clean-bathroom.html?src=uSWT2FNupaTJ_h4SrfGSmg-2-75">Dundanim/Shutterstock</a></span>
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<p>For complex gut health issues, the effectiveness of fecal transplants is either much lower, or not proven. Of <a href="https://www.ncbi.nlm.nih.gov/pubmed/27152872">two published studies</a> of fecal transplants for inflammatory bowel disease, for instance, one found a low effect and one no effect.</p>
<p>Although clinical trials of fecal transplants have reported few problems, we should be <a href="http://mbio.asm.org/content/7/3/e00572-16.short?related-urls=yes&legid=mbio;7/3/e00572-16">alert to the risk</a>. There have been reports of patients showing unexpected weight gain after treatment, for instance. This may be attributable to the engineered microbiota, or may simply reflect that they are no longer seriously ill. </p>
<p>For issues of long-term safety and effectiveness, there are still <a href="http://mbio.asm.org/content/7/3/e00572-16.short?related-urls=yes&legid=mbio;7/3/e00572-16">far more questions</a> than there are answers. </p>
<h2>Probiotics</h2>
<p>Modern lifestyle changes in diet and hygiene have dramatically changed what microbes we are exposed to and how successful they are in colonising us. Our microbiome has changed and we seem to have lost some benefits. Probiotics aim to restore these.</p>
<p>Probiotic can be a confusing term, since its use in marketing creates the perception that any product for human consumption that contains specific live bacteria is a probiotic. This contrasts with the definition used by health regulators around the world: probiotics are <a href="https://www.ncbi.nlm.nih.gov/pubmed/24473361">live bacteria</a> that, when taken in sufficient amounts, confer a health benefit.</p>
<p>The issue revolves around whether the specific bacteria being ingested are what is actually delivering a particular health benefit. There is a lot of marketing hype around products containing good bacteria that “may improve” wellbeing or immune function. </p>
<p>Products that contain live bacteria, such as yoghurt, fermented milk drinks, or pills, contain bacteria that are considered beneficial and are generally recognised as safe. But this is not to say that consuming the product will deliver a known health benefit (the probiotic definition).</p>
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<img alt="" src="https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/142433/original/image-20161020-840-14t4mjs.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Yoghurts are safe but won’t necessarily improve the health of your gut.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-384699205.html">ninikas/Shutterstock</a></span>
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<p>There are many examples where probiotics have been shown to be useful in controlled clinical trials. One example is the use of probiotics in preterm births. Premature babies are at high risk of developing serious illness because they lack beneficial microbes. Probiotic treatments have <a href="http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(15)01090-9/abstract">consistently been found</a> to lower the risk. </p>
<p>Probiotics work most effectively when directly addressing the cause of a disease. </p>
<p>For more complex issues or general health improvement, the story with probiotics is less clear cut. Most probiotic bacterial strains do not actually permanently colonise your gut. So to get any benefit for chronic conditions, you need to continually take them. </p>
<p>The next generation of probiotics are starting to address these issues.</p>
<h2>Next-generation probiotics</h2>
<p>There is great cause for optimism the next generation of microbiome-based therapies will offer significant advances. You don’t restore a complex ecosystem by throwing in one species and expecting it to survive, let alone fix everything. New approaches to probiotics aim to change the ecology of the gut. </p>
<p><a href="http://www.nature.com/nbt/journal/v31/n9/full/nbt.2680.html">Recent studies</a> using cocktails of probiotic species have had encouraging results in experimental studies of mice with inflammatory bowel conditions. The goal is to inoculate with networks of bacteria rather than a single strain. Such networks are more able to deliver complex functions or to displace problem bacteria. </p>
<p>A new generation of biotech companies is developing microbiome-based probiotic pills (crapsules) as alternatives to fecal transplants for treating <em>C. difficile</em>. Although <a href="http://jid.oxfordjournals.org/content/early/2016/02/04/infdis.jiv766.abstract">early studies</a> were very promising and hailed as a breakthrough therapy, a recent phase two trial was less successful. It’s clear there is potential here, but further work is needed. </p>
<p>Although we are in the early stages of the microbiome-engineering era, the future is bright.</p>
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<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65480/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andrew Holmes receives funding from Australian Research Council and National Health Medical Research Council.</span></em></p><p class="fine-print"><em><span>Laurence Macia receives funding from the NHMRC, Sydney University and Monash University.</span></em></p><p class="fine-print"><em><span>Stephen J Simpson receives funding from the Australian Research Council and the National Health and Medical Research Council. He is Executive Direct of Obesity Australia (unpaid).</span></em></p>The modern lifestyle, particularly diet and hygiene changes, have altered our relationship with our microbes. But can we restore it?Andrew Holmes, Associate Professor, University of SydneyLaurence Macia, Senior Research Fellow in Physiology, School Medical Sciences, University of SydneyStephen J Simpson, Professor, ARC Laureate Fellow & Academic Director, The Charles Perkins Centre, University of SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651032016-10-13T19:10:30Z2016-10-13T19:10:30ZFat or thin: can the bacteria in our gut affect our eating habits and weight?<figure><img src="https://images.theconversation.com/files/141378/original/image-20161012-8382-65yoyp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The gut of an obese person is more likely to contain bacteria that inflame the gastrointestinal tract and damage its lining.</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-140709025/stock-photo-fat-and-thin-man.html?src=7rATCkcOkotXDz6OD6y3yA-1-36">Undrey/Shutterstock</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come and whether there’s anything we can do to improve the health of our gut.</em></p>
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<p>When we can’t lose weight, we tend to want to blame something outside our control. Could it be related to the microbiota – the bacteria and other organisms – that colonise your gut? </p>
<h2>You are what you eat</h2>
<p>Our gut harbours some trillion microorganisms. These are key in harvesting energy from our food, regulating our immune function, and keeping the lining of our gut healthy. </p>
<p>The composition of our gut microbiota is partly determined by our genes but can also be influenced by lifestyle factors such as our diet, alcohol intake and exercise, as well as medications. </p>
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<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
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<p>The bacteria in the gut obtain energy for growth when we metabolise nutrients from food. So our diet is a crucial factor in regulating the type of bacteria that colonise our gut. </p>
<p>One key role of the gut microbiota is degrading the carbohydrates we can’t digest into short-chain fatty acids. These help regulate our metabolism and are also important for keeping our colon cells healthy.</p>
<p>Changes in our diet <a href="http://www.nature.com/nature/journal/v505/n7484/full/nature12820.html">can rapidly change</a> the gut microbiota. Generally, a high-fibre diet which is low in saturated fat and sugar is associated with a healthier gut microbiome, characterised by a greater diversity of organisms. </p>
<p>On the other hand, diets high in saturated fat and refined sugars with low fibre content reduce the microbial diversity, which is bad for our health.</p>
<p>Our <a href="https://theconversation.com/eating-healthily-during-the-week-but-bingeing-on-weekends-is-not-ok-for-your-gut-53374">animal studies have shown</a> that consuming an unhealthy diet for only three days a week has detrimental effects on the gut microbiota, even when a healthy diet is eaten for the other four days.</p>
<p>This may be because the gut microbiota are under selective pressure to manipulate the hosts’ eating behaviour to increase their own fitness. This <a href="http://onlinelibrary.wiley.com/doi/10.1002/bies.201400071/abstract">may lead to cravings</a>, akin to your system being “hijacked” by your microbiota.</p>
<h2>Can gut microbiota changes lead to obesity?</h2>
<p>Bacteria in humans fall into two major classifications: bacteroidetes and firmicutes. Obesity is associated with a reduction in the ratio of bacteroidetes to firmicutes but weight loss <a href="http://www.nature.com/nature/journal/v444/n7122/abs/4441022a.html">can reverse this shift</a>. </p>
<p>Many studies have found that the gut of an obese person is more likely to contain bacteria that inflame the gastrointestinal tract and damage its lining. This allows the bacteria in the gut to escape.</p>
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<a href="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=580&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=580&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=580&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=729&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=729&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=729&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">The gastrointestinal tract.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-376886146/stock-vector-human-digestive-system-digestive-tract-or-alimentary-canal-including-text-labels.html?src=SI78-VNDcYwFNyofukksYg-2-56">Christos Georghiou/Shutterstock</a></span>
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<p>We still don’t know definitively if changes in the gut microbiota from an unhealthy diet can contribute to obesity. Most evidence supporting this hypothesis comes from <a href="http://www.nature.com/ismej/journal/v7/n4/full/ismej2012153a.html">animal studies</a>; for instance, the transfer of faecal material from an obese human can lead to weight gain in a recipient mouse.</p>
<p>One possibility is that the obese microbiota may be more efficient in harvesting energy, in part, by influencing the host to eat foods which favour its growth. This could ultimately contribute to weight gain. </p>
<h2>Gut changes after weight-loss surgery</h2>
<p><a href="https://theconversation.com/explainer-the-risks-and-benefits-of-bariatric-surgery-22696">Bariatric surgeries</a> such as gastric bypass, are one of the most effective treatments for obesity because they reduce the size of the stomach. This limits how much food can be eaten and has also been shown to promote the release of <a href="http://www.nature.com/ijo/journal/vaop/ncurrent/full/ijo2016121a.html">hormones</a> which make us feel full.</p>
<p>But other factors may be involved. Intriguingly, some patients report a shift in <a href="http://www.nature.com/ejcn/journal/v67/n2/full/ejcn2012208a.html">food preference</a> away from energy-dense foods after surgery. This may contribute to the success of the procedure. </p>
<p><a href="http://ajcn.nutrition.org/content/early/2013/05/29/ajcn.113.058743">Gastric bypass-induced weight loss</a> has also been associated with increased diversity of the gut microbiota. But how much this contributes to the success of the procedure remains to be determined. </p>
<p>One possibility is that the changes in food preferences reported in bariatric patients may relate to changes in the composition of their gut microbiota.</p>
<h2>How gut microbiota affect our behaviour</h2>
<p>Apart from regulating gut health, there is compelling experimental evidence that gut microbiota play a role in regulating mood.</p>
<p>Several studies have shown that depression is associated with changes in the gut microbiome of humans. </p>
<p><a href="http://www.nature.com/mp/journal/v21/n6/full/mp201644a.html">Depressed patients</a> showed changes in their abundance of firmicutes, actinobacteria and bacteroidetes. When these patients’ gut microbiota was transferred to mice, the mice showed more depressive behaviour than mice that received biota from healthy people. </p>
<p>More work still needs to be done as it is unclear whether this may indicate a causal relationship, or be related to other factors associated with depressive disorders such as a poor diet, changed sleep patterns and drug treatment.</p>
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<img alt="" src="https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/141379/original/image-20161012-8382-qbp8my.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Depression is associated with changes in the microbiome.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-391673635/stock-photo-young-exhausteddepressedconcentrated-woman-sitting-in-her-room-or-office-with-french-windows-in-the-darkstudies-late-at-nightstaying-up-late-overworkingfeeling-under-pressure-and-hea.html?src=_lvuzPLVm0tsnyC5RW1RzQ-2-33">Fulltimegipsy/Shutterstock</a></span>
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<p>Emerging evidence suggests that gut microbiota can influence other behaviours through the “microbiota-gut-brain axis”. Put simply, the gut and the brain communicate in part via the microbiota, which links the emotional and cognitive centres of the brain with our intestinal functions.</p>
<p><a href="https://www.ncbi.nlm.nih.gov/pubmed/27448745">Recent work</a> from our lab showed that rats consuming diets high in saturated fat or sugar, for just two weeks, had impaired spatial memory. These rats consumed the same amount of energy as the control rats (those on a regular diet) and were also a similar body weight. </p>
<p>We found that the memory deficits were associated with changes in the gut microbiota composition and genes related to inflammation in the <a href="https://theconversation.com/explainer-what-happens-in-the-hippocampus-32589">hippocampus</a>, which is a key brain region for memory and learning. </p>
<p>Similar memory deficits <a href="https://www.ncbi.nlm.nih.gov/pubmed/25173628">have also been reported</a> when healthy mice were transplanted with microbiota from overweight mice who had been fed a high-fat diet. </p>
<p>Together, studies such as these suggest the gut microbiota could play a causal role in regulating behaviour. This may, in part, be due to the different microbiota profiles influencing the production of key transmitters such as serotonin. </p>
<h2>What can you do now?</h2>
<p>Further research is needed into the relationship between poor diet, the gut microbiota and behavioural changes. In the long term, such knowledge may be harnessed to develop targeted therapeutic interventions to replace relevant microbiota diminished by an unhealthy lifestyle.</p>
<p>Meanwhile, the good news is that the gut microbiota can change relatively quickly and we have the capacity to promote the growth of beneficial bacteria which may ultimately improve a range of health outcomes. Eating a healthy diet of unprocessed foods, including adequate fibre, avoiding excess alcohol and getting enough exercise are key.</p>
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<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65103/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Margaret Morris receives funding from the National Health and Medical Research Council of Australia, and serves on the board of Nutrition Australia (NSW). </span></em></p><p class="fine-print"><em><span>Jessica Beilharz does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>When we can’t lose weight, we tend to want to blame something outside our control. Could it be related to the mictobiota – the bacteria and other organisms – that colonise your gut?Margaret Morris, Professor of Pharmacology, Head of Pharmacology, UNSW SydneyJessica Beilharz, PhD candidate, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651042016-10-12T19:07:26Z2016-10-12T19:07:26ZGut instinct: how the way you’re born and fed affect your immune system<figure><img src="https://images.theconversation.com/files/141364/original/image-20161012-8389-1534mob.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The mode of delivery has a big impact on an infant's microbiota, the bacteria that live in the gut.</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-50320798/stock-photo-baby-being-born-via-caesarean-section-coming-out.html?src=AnCMrsfQ0twnnPp1S4TOMA-1-4">Martin Valigursky/Shutterstock</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come and whether there’s anything we can do to improve the health of our gut.</em></p>
<hr>
<p>We used to think foetuses had <a href="http://jn.nutrition.org/content/138/9/1791S.full">no</a> bacteria in their gastrointestinal tract (the gut) until they began to accumulate microbes (bacteria, viruses and other bugs) on their way through their mother’s vagina. </p>
<p>But this theory was challenged when bacteria <a href="http://www.ncbi.nlm.nih.gov/pubmed/19783002">was found</a> in meconium (the first poo) of premature babies. This, of course, travelled through the gut, accumulating microbes on the way. </p>
<p>What’s clear is that newborns have little (if any) diversity in their microbiota – the collection of bacteria that accumulate in the gut. This increases as they’re exposed to different environments. </p>
<p>The particular makeup of a newborn’s gut microbes is important as it has been shown to affect their <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3983973/">risk of developing certain diseases</a> in childhood and adulthood. </p>
<h2>Vaginal or caesarean birth?</h2>
<p>The mode of delivery has a big impact on an infant’s microbiota. During natural delivery, the direct contact with the mother’s vaginal and intestinal flora <a href="http://www.ncbi.nlm.nih.gov/pubmed/18716189">help shape a newborn’s gut bacteria</a> colonisation. Newborns delivered via caesarean section don’t have this direct contact.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YB-8JEo_0bI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
</figure>
<p><a href="http://www.ncbi.nlm.nih.gov/pubmed/20566857">One study</a> found that newborns born vaginally were colonised by <em>Lactobacillus</em> whereas caesarean delivery newborns were colonised by a mixture of bacteria typically found on the skin and in hospitals, such as <em>Staphylococcus</em> and <em>Acinetobacter</em>. </p>
<p>These early differences tend to be sustained. <a href="http://www.ncbi.nlm.nih.gov/pubmed/9890463">One study showed</a> the distinct gut flora of infants born by caesarean delivery persisted at six months after birth. Faecal <em>Clostridia</em> numbers in seven-year-old children born vaginally were <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1774211/">found to be significantly higher</a> than in children of the same age born via caesarean. </p>
<p>But we still don’t know how this impacts on children’s health and the risk of disease. </p>
<h2>The developing immune system</h2>
<p>We’re beginning to realise gut bacteria plays an important role in the growth of infants’ immune systems. One way this could occur is by <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4829075/">altering the development</a> of the white blood cells that provide a first-line defence against invading microbes: bugs that make us sick. </p>
<p>Research shows <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4144825">mice born in a germ-free environment</a> have fewer of these white blood cells compared to healthy mice with a normal gut bacteria population. Such mice are also more prone to bacterial infection. </p>
<p>Allergic diseases such as asthma and hay fever <a href="http://www.ncbi.nlm.nih.gov/pubmed/16297144">appear more often</a> in infants after caesarean delivery than after vaginal delivery. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/141366/original/image-20161012-8430-16k2o6l.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Children who weren’t breast-fed are at higher risk of asthma.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-458352256/stock-photo-asthma-treatment-child.html?src=z56JbZJnuStNpDU6ibtKkQ-1-4">kritsada doungdao/Shutterstock</a></span>
</figcaption>
</figure>
<p>Children born by caesarean delivery are also significantly more likely to be <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4847338/">hospitalised for acute gastroenteritis</a> and to develop <a href="http://www.ncbi.nlm.nih.gov/pubmed/20478942">coeliac disease</a>.</p>
<p>It’s important to note that not all caesarean deliveries are the same. Some women have caesarean sections after a long labour where her waters have broken. In this case, the infant would be exposed to quite a different microbial environment than a planned caesarean section carried out before her waters have broken. </p>
<h2>Breast- or bottle-fed?</h2>
<p>Breast-fed newborns <a href="http://www.ncbi.nlm.nih.gov/pubmed/21497661">have</a> a distinctly different gut microbiome to other newborns. They have higher proportions of the beneficial bacterial species <em>Bifidiobacterium</em> than <a href="https://www.ncbi.nlm.nih.gov/pubmed/10630441">formula-fed infants</a>. This is likely due to breast milk containing a type of prebiotic that facilitates the growth of bacteria such as as <a href="https://www.ncbi.nlm.nih.gov/pubmed/15220665"><em>Bifidobacterium</em></a>.</p>
<p>Interestingly, when breast-fed infants are supplemented with formula feeds, their gut microbiota <a href="https://www.ncbi.nlm.nih.gov/pubmed/26752321">resembles infants</a> who are exclusively formula-fed. </p>
<p>What does this mean for infants’ risk of developing disease?</p>
<p>A <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3446306">US study</a> has shown that breast-fed babies had a gut microbiome that was richer in genes associated with “virulence”: the ability to fight off antibiotics and toxic compounds. These same babies also developed changes in the genes of their gut immune system that allowed them to better fight off infection. </p>
<p>This suggests that breast milk can promote a healthy crosstalk between the baby’s immune system and the gut microbiome. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/141365/original/image-20161012-8401-h0uaai.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Breast-fed newborns have a distinctly different gut microbiome to other newborns.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-454381816/stock-photo-mother-breastfeeding-her-newborn-baby-girl-during-the-lunch-breastfeeding-on-demand-instagram-style-effect-applied.html?src=9MyTFDAc6WF3vRQ-HIWEfw-1-4">DeymosHR/Shutterstock</a></span>
</figcaption>
</figure>
<p>Breast-feeding has been shown to reduce the development of <a href="http://www.ncbi.nlm.nih.gov/pubmed/10232646">necrotising enterocolitis</a> (where parts of the bowel die off) in newborns, allergic and autoimmune diseases in childhood, including <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2083075/">coeliac disease</a>, <a href="http://www.ncbi.nlm.nih.gov/pubmed/22189253">type 1 diabetes</a> and <a href="https://www.ncbi.nlm.nih.gov/pubmed/24727807">asthma</a>. </p>
<h2>Vaginal seeding</h2>
<p>What if your child is born via a caesarean section and can’t be breastfed? </p>
<p>Don’t worry, not all such infants will be at a greater risk of developing autoimmune and allergic diseases. A whole host of environmental and genetic factors play a role in determining individual risk. </p>
<p><a href="https://theconversation.com/explainer-what-is-vaginal-seeding-55187">Vaginal seeding</a> has recently been proposed as one way infants born by caesarean section might gain some of the protective effects of environmental exposure for their gut microbiota. </p>
<p>A <a href="http://www.ncbi.nlm.nih.gov/pubmed/26828196">proof-of-concept study</a> in 18 infants published earlier this year showed that transferring vaginal fluid to newborns (via a swab across their mouth, nose and face) shortly after delivery by caesarean section can result in microbiome profiles resembling that of infants delivered vaginally. </p>
<p>It is unknown though whether colonisation in this way is partially or fully equivalent to the microbial transfer at labour. We also don’t know whether later health outcomes in these infants are affected by the practice. </p>
<p><a href="http://www.ncbi.nlm.nih.gov/pubmed/26906151">Some expert clinicians</a> warn against vaginal seeding because of the potential for unrecognised infections to be transmitted from mother to newborn. There is <a href="http://www.ncbi.nlm.nih.gov/pubmed/27236858">a risk</a>, for example, of transmitting undiagnosed group B <em>Streptococcus</em> to newborns, given <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/streptococcal-infection-group-b">12 to 15% of women</a> have this organism in vaginal fluid. </p>
<h2>Better ways to catch up</h2>
<p>For now, it’s more sensible to focus on the practices that <a href="http://www.utswmedicine.org/stories/articles/year-2016/c-section-microbiome.html">have been shown to</a> promote microbiome development in newborns delivered by caesarean. These include delaying the first bath until after 12 hours, placing the newborn on the mother’s skin in the first few minutes after delivery and breastfeeding in the operating room, if permissible. </p>
<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=900&fit=crop&dpr=1 600w, https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=900&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=900&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1130&fit=crop&dpr=1 754w, https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1130&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/141367/original/image-20161012-8385-4zuokl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1130&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Skin-to-skin contact after birth is important for the development of the infant’s microbiota.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-99349961/stock-photo-newborn-baby-on-his-mothers-arms-right-after-delivery.html?src=pp-same_model-99349967-1&ws=1">Kati Molin/Shutterstock</a></span>
</figcaption>
</figure>
<p>There has been much effort made in simulating the composition of human milk through adding live gut bacteria (probiotics) as well as non-digestible fibres (prebiotics) <a href="http://www.ncbi.nlm.nih.gov/pubmed/19840609">to formula</a>. This is <a href="http://www.ncbi.nlm.nih.gov/pubmed/19770768">thought to assist</a> microbial colonisation and immune responses in formula-fed infants in a similar way to breast feeding.</p>
<p>But hard data is lacking though on whether this approach can lead to a real-life benefit, particularly when it comes to reducing the risk of allergic disorders. </p>
<p>Fortunately, a large clinical research project in New Zealand – the <a href="https://bmcpregnancychildbirth.biomedcentral.com/articles/10.1186/s12884-016-0923-y">Probiotics in Pregnancy study</a> – will soon be able to answer this question. </p>
<p>Four hundred pregnant women expecting infants at high risk of allergic disease were given either a probiotic <em>Lactobacillus rhamnosus</em> or placebo – 14 to 16 weeks into their pregnancy until they gave birth, or for six months after if they breast-fed.</p>
<p>The researchers will then check if the infant develops allergies such as eczema. The results will be available before too long and may be instrumental in helping to shape health policy. </p>
<hr>
<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65104/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Vincent Ho does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The particular makeup of a newborn’s gut microbes is important as it has been shown to affect their risk of developing certain diseases later in childhood and adulthood.Vincent Ho, Senior Lecturer and clinical academic gastroenterologist, Western Sydney UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651062016-10-11T19:04:53Z2016-10-11T19:04:53ZWhat the consistency of your poo says about your health<figure><img src="https://images.theconversation.com/files/140636/original/image-20161006-20134-nmmjr4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What does it mean when it's too hard or too soft?</span> <span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-424455349/stock-photo-man-looking-in-the-toilet-bowl.html?src=pp-same_model-427517689-5&ws=1">Nomad_Soul/Shutterstock</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come and whether there’s anything we can do to improve the health of our gut.</em></p>
<hr>
<p>Number twos are a tricky subject. We all do them. Indeed, excreting waste is critical to life. But polite society and its rules of etiquette ensure we’re rarely brave enough to speak about them. </p>
<p>The faeces (or stools) we produce can provide a valuable real-time window into the health of your large bowel (or colon) and gastrointestinal tract. So let’s put those rules aside.</p>
<p>Scientists research many odd topics and stool form is no exception. In 1998, Stephen Lewis and Ken Heaten from the University of Bristol developed a <a href="http://www.continence.org.au/pages/bristol-stool-chart.html">seven-point stool form scale</a>, ranging from constipation (type 1) to diarrhoea (type 7).</p>
<p>Today, the Bristol Stool Chart allows people with gastrointestinal symptoms to clearly describe to their doctor what they are seeing in the toilet without having to provide samples.</p>
<hr>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=764&fit=crop&dpr=1 600w, https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=764&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=764&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=960&fit=crop&dpr=1 754w, https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=960&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/141158/original/image-20161011-3909-p1j1kp.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=960&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
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<hr>
<p>For most of us, the form of stool we excrete can vary widely depending, in part, on what we’ve been doing. A period of dehydration, perhaps associated with a day of sustained exercise, or the delaying of a bowel movement, may be followed by a drier stool form than normal. </p>
<p>Conversely, an unusually spicy meal might be followed by a bowel movement with a looser stool. </p>
<h2>How should your stools look?</h2>
<p>Ideally, stools should be easy to pass without straining and without any intense sense of urgency. </p>
<p>On the Bristol Stool Chart, these are types 3, 4 and 5: sausage-like with some cracks in the surface, up to 2 to 3 cm in diameter; longer sausage or snake-like with a smooth consistency, similar to that of toothpaste with a typical diameter of 1 to 2 cm; or soft blobs with clear cut edges. </p>
<p>While arguably easier to clean up, the drier stool forms (types 1 and 2) tend to compact into large stool that can apply long term pressure to and abrade the lining of the large bowel.</p>
<p>During a bowel movement, dry stools may distend the anal canal beyond its normal aperture. This may require straining – and pain – to pass. </p>
<p>Straining to pass dry stools increases the risk of laceration of the anus, haemorrhoids, prolapse and the condition <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/diverticulosis-and-diverticulitis">diverticulosis</a>. This is when pouches form on the wall of the large bowel due to over-distension. These can become sites for infection or inflammation. </p>
<p>Watery stool forms may be associated with gut infections, for example with a gut parasite like <a href="https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/gastroenteritis-giardiasis"><em>Giardia</em></a>, or an <a href="http://www.mayoclinic.org/diseases-conditions/inflammatory-bowel-disease/basics/definition/con-20034908">inflammatory disorder</a> such as Crohn’s disease. </p>
<p>As a rule, softer but not watery stool forms are best. </p>
<p>Any change of bowel habit that leads to the sustained production of drier stools and a sense of incomplete emptying – or watery stools and a feeling of urgency – should be discussed with your doctor. </p>
<h2>Why does water matter?</h2>
<p>Even to the casual toilet bowl observers among us, the most obvious differentiating factor between stool forms is their water content. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140639/original/image-20161006-20123-1xfxxwu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Drinking enough water is important for good bowel health.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-2867845/stock-photo-young-boy-gulping-down-water-from-a-tap.html?src=TTOBZ4pTQSnoZK-F-MU_Ng-2-34">David H.Seymour/Shutterstock</a></span>
</figcaption>
</figure>
<p>The large bowel is an amazing recycling and repurposing centre for the body. Water recycling is one of its key functions. </p>
<p>Every day, our bodies invest around 9 litres of fluids into the digestion of food, including around 1.5 litres of saliva, 2.5 litres of stomach secretions and 0.8 litres of bile. But clearly we don’t defecate anywhere near this volume. </p>
<p>The longer it takes for digested food to pass through the large bowel, the more water gets reclaimed and the drier the stool becomes. So factors affecting the transit rate of food through our gastrointestinal tract will have significant influence on stool form. </p>
<p>Affluence and lifestyle impact on transit time. Antibiotics, pain killers (particularly opiate-containing drugs such as Endone but also more common pain-killers containing codeine) as well as physical inactivity all reduce how well the gut contracts. This slows the passage of food through the large bowel, which can lead to constipation.</p>
<h2>What about diet?</h2>
<p>Our diets also play a significant part in driving stool form and health. </p>
<p>Observational studies performed in south and eastern Africa in the 1970s and 80s compared the gastrointestinal health of Caucasians eating a Western-style diet and native Africans living a <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1588096/">traditional lifestyle</a>. The researchers found drier stool forms and constipation were more common in people consuming <a href="http://www.ncbi.nlm.nih.gov/pubmed/11427691">Western-style diets</a>. </p>
<p>This was associated with increased incidence of bowel cancer, inflammatory bowel diseases as well as other chronic diseases of rising incidence in Western societies. </p>
<p>The results were attributed to differing levels of fibre in the diets of these two populations and these conclusions have been clearly confirmed for bowel cancer in <a href="http://www.wcrf.org/int/research-we-fund/continuous-update-project-cup">numerous studies</a>.</p>
<p>Fibre impacts on transit time, stool form and health in two ways. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=523&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=523&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140641/original/image-20161006-20132-113td4o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=523&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Western diets are more likely to leave us constipated.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-213705436/stock-photo-sofia-bulgaria-august-23-2014-mcdonalds-meal-on-a-stret-background-near-their-restaurant.html?src=lwq_-VF5lAIkpq_Q_toYwA-1-49">SSokolov/Shutterstock</a></span>
</figcaption>
</figure>
<p>First, when a healthy, well-hydrated person eats fibrous foods such as wheat bran with lots of roughage, the food takes up water and swells. This increases the volume of the stool, softening it, stimulating more rapid transit. At the same time, it dilutes and more rapidly clears any toxins that may have been ingested with the food. </p>
<p>More potent components of dietary fibre also exist: fermentable carbohydrates such <a href="http://www.csiro.au/hungrymicrobiome/food.html">resistant starch</a> (a form of starch that is not digested in the small intestine), <a href="https://www.cancer.gov/publications/dictionaries/cancer-drug?cdrid=38642">beta glucans</a> and <a href="https://www.sciencedaily.com/releases/2013/07/130716115728.htm">fructo-oligosaccharides</a>, which are commonly found in whole grains, legumes, pulses, fruit and vegetables. These are a key nutritional source for the trillions of bacteria that inhabit the large bowel (the gut microbiota). </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YB-8JEo_0bI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
</figure>
<p>Key waste products of this bacterial feast, short-chain fatty acids, are <a href="http://www.cell.com/cell/pdf/S0092-8674(16)30592-X.pdf">like gold to our bodies</a>. One of these short-chain fatty acids, <a href="http://www.livestrong.com/article/553726-what-foods-are-high-in-butyrate/">butyrate</a> (which is also the food acid that gives parmesan cheese its haunting aroma), reduces transit time by strengthening contraction of muscles lining the large bowel. </p>
<p>On the way, these short-chain fatty acids strengthen, grow and repair the cell layers that line the large bowel. They destroy cancerous cells, reduce inflammation and pain in the gut, and enhance satiety. Worth feeding, you might say! </p>
<p>But one gastronomic casualty of the Westernisation of our diets has been fibre. A typical Westerner may consume as little as 12-15g of fibre per day. While no upper limit for daily fibre intake has been defined, healthy Australians are recommended to consume at least <a href="https://www.nrv.gov.au/nutrients/dietary-fibre">30g of dietary fibre</a> per day, with around 15-20g of that comprising resistant starch. </p>
<p>So clearly we have some distance to go. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140647/original/image-20161006-20139-7az6hp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">We need 30g of fibre a day.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-191953970/stock-photo-healthy-breakfast-with-high-fibre-bran-flakes-blueberry-and-banana.html?src=cOSRlSf4qatnmJvgzJEz-g-1-0">Brian A Jackson/Shutterstock</a></span>
</figcaption>
</figure>
<p>There is a caveat here, however. If you have gastrointestinal symptoms – such as an upset stomach, nausea, vomiting, and diarrhoea – fibre may not always help. You may need to carefully consider the type of fibre you consume, with the help of your doctor. </p>
<p>The roughage component of some fibre sources may exacerbate symptoms for people with <a href="https://www.bowelcanceraustralia.org/diverticular-disease">diverticular disease</a>, for instance. </p>
<p>Symptoms of irritable bowel syndrome may be exacerbated by fibre sources rich in <a href="http://www.med.monash.edu/cecs/gastro/fodmap/">fermentable fructose oligo, di or mono saccharides and polyols</a> (FODMAP). This includes onion, garlic, apples, pears, milk, legumes, some breads and pasta, and cashews. </p>
<p>For most of us, though, more fibre in our diets should reduce food transit times, soften stools, make bowel movements more comfortable and improve bowel health. </p>
<hr>
<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65106/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Trevor Lockett receives funding from NHMRC and the Cancer Councils of Victoria, New South Wales, Queensland and South Australia. </span></em></p>For most of us, the form of stool we excrete can vary widely depending, in part, on what we’ve been doing.Trevor Lockett, Group Leader, Personalised Health, CSIROLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651052016-10-10T19:03:11Z2016-10-10T19:03:11ZHealthy guts are swarming with bugs, so what do they do?<figure><img src="https://images.theconversation.com/files/141053/original/image-20161010-2596-xi09el.png?ixlib=rb-1.1.0&rect=0%2C0%2C1920%2C948&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The exact composition of each person’s microbiota is as unique as their finger prints.</span> <span class="attribution"><span class="source">The Conversation</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come and whether there’s anything we can do to improve the health of our gut.</em> </p>
<hr>
<p>The healthy human body is swarming with microorganisms. They inhabit every nook and cranny on the surfaces of our body. But by far the largest collection of microorganisms reside in our gastrointestinal tract – our gut. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YB-8JEo_0bI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
</figure>
<p>These tiny organisms, which can only be seen with the aid of a microscope, make up our microbiota. The combination of microbiota, the products it makes, and the environment it lives within, is called the microbiome. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=580&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=580&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=580&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=729&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=729&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=729&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The gastrointestinal tract.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-376886146/stock-vector-human-digestive-system-digestive-tract-or-alimentary-canal-including-text-labels.html?src=SI78-VNDcYwFNyofukksYg-2-56">Christos Georghiou/Shutterstock</a></span>
</figcaption>
</figure>
<p>Great advances in DNA sequencing technologies have enabled us to study the gut microbiota in intricate detail. We can now take a census of all the microorganisms that are in the microbiota to help us understand what they are doing.</p>
<p>Typically, our gut microbiota consists of several thousand different types of bacteria, as well as other microbes such as viruses and yeasts. Some types will be in abundance, while other types will be rare. </p>
<p>The exact composition of each person’s microbiota is as unique as their finger prints. But unlike finger prints, the microbiota is constantly changing. </p>
<p>Microbes start to colonise our gut and skin the moment we are born. The mode of birth, either natural or by caesarean, determines the sort of microbes a baby first contacts. This <a href="https://www.ncbi.nlm.nih.gov/pubmed/9890463">can have a profound effect</a> on the early development of the microbial populations that contribute to the microbiota.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140244/original/image-20161004-20217-17lzg3f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tiny organisms begin to colonise the gut as soon as we’re born.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-331803158/stock-photo-midwife-holding-up-a-vernix-covered-newborn-just-after-he-was-born-in-the-delivery-room-being-peaceful-and-serene-still-attached-with-umbilical-cord-new-life-birth-experience-concept.html?src=Y3HY1QGSQzFTIgypgjbqHw-1-9">zlikovec/Shutterstock</a></span>
</figcaption>
</figure>
<p>The structure of the microbiota – that is, what microbes are present and the relative numbers of each type – undergoes significant change from its establishment at birth until it matures in early adolescence. </p>
<p>In healthy adults, changes over time are likely to be small. But major shifts in composition can occur when we radically change our diet or take antibiotics, which are, of course, designed to kill bacteria. </p>
<p>It’s also been found that, like our own body, the composition of our microbiota <a href="https://www.ncbi.nlm.nih.gov/pubmed/26785481">changes in old age</a>, including a loss of diversity. </p>
<p>Our microbiota is not an accidental, free-loading passenger living in our gut and stealing the nutrients from our food. Over the millennia we have evolved with our microbiota. We now know it can affect many aspects of our biology, from our digestive system to our brain function.</p>
<p>How our bodies develop and function is dictated by our genes. We have <a href="https://www.ncbi.nlm.nih.gov/pubmed/24939910">approximately 20,000 genes encoded</a> in our genetic material.</p>
<p>The different microbes that make up our microbiota have their own genes. As a rough estimate, the 2,000 different types of microbes may, on average, each carry 3,000 genes. That means the microbiota carries six million genes. Although many will have similar functions, it still indicates the microbiota has a much more complex =genetic complement= than we ourselves have. </p>
<p>This genetic complement of the microbiota means it can do things other parts of the body cannot. Our microbiota provides digestive enzymes to allow us to use food that otherwise we could not digest. It provides essential vitamins we cannot make ourselves. And it interacts with our hormonal and neural systems to help shape our physiology. </p>
<p>Perhaps most important of all, it helps to develop our immune system to fight off bugs. The body must be able to distinguish between the beneficial members of the healthy microbiota and invading pathogenic microorganisms that can cause disease. The immune system has to learn to live with and nurture the microbiota while fighting off pathogens. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140247/original/image-20161004-20217-d06tr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Microbiota help develop our immune system.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-342967553/stock-photo-morning-therapy-ill-man-with-two-pills-and-a-glass-of-water.html?src=ioJ_v07F2hpasoa8GwWa1Q-2-48">kikovic/Shutterstock</a></span>
</figcaption>
</figure>
<p>Disruption of the correct interaction between microbiota and the immune system may be one of the causes of the massive increase over the past few decades in immune-related diseases, such as diabetes, food allergies, rheumatoid arthritis, and inflammatory bowel disease. </p>
<p>Many of these diseases seem to be diseases of affluence, probably influenced by <a href="https://www.ncbi.nlm.nih.gov/pubmed/27617196">poor diets</a> and <a href="https://www.ncbi.nlm.nih.gov/pubmed/27471720">excessive cleanliness</a>, affecting the early establishment of an appropriate microbiota.</p>
<p>The intimate connection between host and microbiota and the rich contribution that each brings to the partnership has resulted in the concept of a metaorganism. This recognises that as humans, we are really the product of the mutual cooperation between our own bodies and our microbiota. </p>
<p>Indeed, our microbiota is so important and has such specific functions that it’s reasonable to view it as another organ of our body. It’s just as important as our liver or kidneys.</p>
<hr>
<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65105/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Robert Moore receives funding from the Poultry Cooperative Research Centre and the Australian Research Council. </span></em></p>The make-up of our gut is constantly changing and affects everything from our immune system and digestion, to our brain function.Robert Moore, Research Professor of Biotechnology, Head of Host-Microbe Interactions Laboratory, RMIT UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/651072016-10-10T19:03:00Z2016-10-10T19:03:00ZGut feeling: how your microbiota affects your mood, sleep and stress levels<figure><img src="https://images.theconversation.com/files/140435/original/image-20161005-15882-1tk9cu6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">There are several possible ways your gut bacteria could affect your brain.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/anitacanita/1438312590/">Ana C./</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p><em>Our gut does more than help us digest food; the bacteria that call our intestines home have been implicated in everything from our mental health and sleep, to weight gain and cravings for certain foods. <a href="https://theconversation.com/au/topics/gut-series-32096">This series</a> examines how far the science has come and whether there’s anything we can do to improve the health of our gut.</em> </p>
<hr>
<p>The gut microbiota is the community of bugs, including bacteria, that live in our intestine. It has been called the body’s “forgotten organ” because of the important role it plays beyond digestion and metabolism.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/YB-8JEo_0bI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">What is the human microbiome?</span></figcaption>
</figure>
<p>You might have read about the importance of a healthy gut microbiota for a healthy brain. Links have been made between the microbiota and depression, anxiety and stress. Your gut bacteria may even affect how well you sleep. </p>
<p>But it can be difficult to work out exactly how far the science has come in this emerging field of research. So what evidence is there that your gut microbiota affects your brain?</p>
<h2>How does your gut talk to your brain?</h2>
<p>When you’re healthy, bacteria are kept safely inside your gut. For the most part, the bacteria and your gut live in harmony. (The gut has been known to nurture or even <a href="https://cosmosmagazine.com/biology/chemical-messengers-could-make-poo-transplants-obsolete">control the behaviour</a> of the bacteria for your well-being.) </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=580&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=580&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=580&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=729&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=729&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140404/original/image-20161005-14595-l7eper.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=729&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The gastrointestinal tract.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-376886146/stock-vector-human-digestive-system-digestive-tract-or-alimentary-canal-including-text-labels.html?src=SI78-VNDcYwFNyofukksYg-2-56">Christos Georghiou/Shutterstock</a></span>
</figcaption>
</figure>
<p>So how do the bacteria get their signal out? </p>
<p>The best evidence is that the normal channels of communication from your gut are being hijacked by the bacteria. </p>
<p>The gut has a bidirectional relationship with the central nervous system, referred to as the “<a href="http://www.gutmicrobiotaforhealth.com/en/interview-ted-dinan-learning-gut-brain-axis/">gut-brain axis</a>”. This allows the gut to send and receive signals to and from the brain. </p>
<p>A recent <a href="http://www.pnas.org/content/108/38/16050">study</a> found that the addition of a “good” strain of the bacteria lactobacillus (which is also found in yoghurt) to the gut of normal mice reduced their anxiety levels. The effect was blocked after cutting the vagus nerve – the main connection between brain and gut. This suggests the gut-brain axis is being used by bacteria to affect the brain. </p>
<p>This link was clarified in a <a href="http://www.ncbi.nlm.nih.gov/pubmed/25550456">study</a> where bacterial metabolites (by-products) from fibre digestion were found to increase the levels of the gut hormone and neurotransmitter, serotonin. Serotonin can activate the vagus, suggesting one way your gut bacteria might be linked with your brain.</p>
<p>There are <a href="http://www.ncbi.nlm.nih.gov/pubmed/25103109">many other ways</a> gut bacteria might affect your brain, including via bacterial toxins and metabolites, nutrient-scavenging, changing your taste-receptors and stirring up your immune system. </p>
<h2>How can the gut affect your mental health?</h2>
<p>Two human studies looked at people with major depression and found that bacteria in their faeces differed from healthy volunteers. But it’s not yet clear why there is a difference, or even what counts as a <a href="http://www.jwatch.org/na41241/2016/05/27/characteristics-gut-microbiome">“normal” gut microbiota</a>. </p>
<p>In mouse studies, changes to the gut bacteria from antibiotics, probiotics (live bacteria) or specific breeding techniques are associated with anxious and depressive behaviours. These behaviours can be “<a href="http://www.gutmicrobiotaforhealth.com/en/gut-microbiota-changes-may-responsible-depressive-like-behaviours-mice-alterations-host-metabolism/">transferred</a>” from one mouse to another after a faecal microbiota transplant. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140439/original/image-20161005-15906-15jx2ll.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Human studies have found links between mental illness and gut bacteria, but much remains unknown.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-241234900/stock-photo-tram-interior-young-woman-looking-aside-to-other-passengers.html?src=9yzbdDOrs_F5wyc2eRbb0g-1-38">Anna Jurkovska/Shutterstock</a></span>
</figcaption>
</figure>
<p>Even more intriguingly, in a <a href="http://www.ncbi.nlm.nih.gov/pubmed/27491067">study</a> this year, gut microbiota samples from people with major depression were used to colonise bacteria-free rats. These rats went on to show behavioural changes related to depression. </p>
<p>Stress is also likely to be important in gut microbiota and mental health. We’ve known for a long time that stress contributes to the onset of mental illness. We are now discovering bidirectional links between stress and the microbiota. </p>
<p>In rat pups, exposure to a stressor (being separated from their mums) changes their gut microbiota, their stress response, <a href="https://www.sciencedaily.com/releases/2015/07/150728110734.htm">and their behaviour</a>.
Probiotics containing “good” strains of bacteria can reduce their stress behaviours. </p>
<h2>How gut microbiota affects your mood</h2>
<p>Medical conditions associated with changes in mood, such as irritable bowel syndrome (IBS) and chronic fatigue syndrome (CFS), might also be related to gut microbiota. </p>
<p>IBS is considered a “<a href="http://www.ibsclinic.org.au/causes.php?pageId=584&moduleId=186">gut-brain disorder</a>”, since it is often worsened by stress. Half of IBS sufferers also have difficulties with depression or anxiety. </p>
<p>Ongoing <a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734998/">research</a> is investigating whether gut bacteria are one reason for the mood symptoms in IBS, as well as the gastrointestinal pain, diarrhoea and constipation. </p>
<p>Similarly, CFS is a multi-system illness, with many patients experiencing unbalanced gut microbiota. In these patients, alterations in the gut microbiota may contribute to the development of symptoms such as depression, neurocognitive impairments (affecting memory, thought and communication), pain and sleep disturbance. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140437/original/image-20161005-15896-23ejyd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Many people with irritable bowel syndrome and chronic fatigue syndrome have unbalanced gut microbiota.</span>
<span class="attribution"><a class="source" href="http://www.shutterstock.com/pic-123452617/stock-photo-a-man-holds-both-hands-to-his-abdominal-area.html?src=ZAa72DR2SuOfdF-7T42OwQ-2-91">Alice Day/Shutterstock</a></span>
</figcaption>
</figure>
<p><a href="http://www.sciencedirect.com/science/article/pii/S1984006315000632">In a recent study</a>, higher levels of lactobacillus were associated with poorer mood in CFS participants. Some improvements in sleep and mood were observed when patients used antibiotic treatment to reduce gut microbial imbalance.</p>
<p>The exact contributions of stress and other factors such as intestinal permeability (which allows nutrients to pass through the gut) to these disorders are not understood. But the downstream effects seem to be involved in IBS, inflammatory bowel conditions, CFS, depression and chronic pain. </p>
<h2>How our gut affects our sleep</h2>
<p>Our mental health is closely linked to the quality and timing of our sleep. Now evidence suggests that the gut microbiota can influence sleep quality and sleep-wake cycles (our circadian rhythm). </p>
<p>A study this year examined patients <a href="http://www.ncbi.nlm.nih.gov/pubmed/26757840">with CFS</a>. The researchers found that higher levels of the “bad” clostridium bacteria were associated with an increased likelihood of sleep problems and fatigue, but this was specific to females only. This suggests that an unbalanced gut may precipitate or perpetuate sleep problems. </p>
<p>There is emerging evidence that circadian rhythms regulate the gut immune response. The effect of immune cells on the biological clock could provide insights into the possible bidirectional relationship between sleep and the gut. For example, data from <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0097500">animal studies</a> suggests that circadian misalignment can lead to an unbalanced gut microbiota. But this effect can be moderated by diet. </p>
<p>There is growing concern that <a href="http://www.nature.com/nrn/journal/v6/n5/full/nrn1670.html">disruptions</a> to our circadian timing of sleep leads to a range of health issues, such as obesity, metabolic and inflammatory disease, and mood disorders. This is particularly important for shiftworkers and others who experience changes to their sleep/wake patterns. </p>
<h2>What this means for treatment</h2>
<p>In terms of using interventions directed at the gut to treat brain disorders – so called “psychobiotics” – there is a lot of promise but little clear evidence. </p>
<p>Probiotic (live bacteria) treatments in mice have been shown to reduce cortisol, an important stress hormone, and decrease anxious and depressive behaviours. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/140438/original/image-20161005-15896-mp38k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">It’s not as simple as opening a tub of yoghurt.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/stone-soup/6849003064/">jules/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>But there are very few studies in humans. A <a href="http://www.ncbi.nlm.nih.gov/pubmed/26370263">recent systematic review</a> of all the human studies showed the majority do not show any effect of probiotics on mood, stress or symptoms of mental illness.</p>
<p>On the plus side, large studies show us that people who eat a balanced diet with all the usual good stuff (fibre, fresh fruit and vegetables) have lower rates of mental illness as <a href="http://www.ncbi.nlm.nih.gov/pubmed/21957462">adults</a> and <a href="http://www.ncbi.nlm.nih.gov/pubmed/21715296">adolescents</a>. </p>
<p>Clearly, diet affects both the gut microbiota and mental health. Research is ongoing to see whether it is a healthy gut microbiota that underlies this relationship. </p>
<p>A healthy gut microbiota is linked to a healthy brain. However there are only a handful of human studies demonstrating real-world relevance of this link to mental health outcomes. </p>
<p>There is still a way to go before we can say exactly how best to harness the microbiota in order to improve brain function and mental health. </p>
<hr>
<p><em>Read the other articles in our Gut series <a href="https://theconversation.com/au/topics/gut-series-32096">here</a>.</em></p><img src="https://counter.theconversation.com/content/65107/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Paul Bertrand receives funding from National Health and Medical Research Council for projects relating to gastrointestinal health and disease</span></em></p><p class="fine-print"><em><span>Amy Loughman receives funding from the National Health and Medical Research Council. </span></em></p><p class="fine-print"><em><span>Melinda Jackson receives funding from The National Health and Medical Research Council. She has previously received funding from Bioscreen Inc. </span></em></p>Links have been made between the community of bacteria in your gut and depression, pain, stress and sleep. So what does the science say?Paul Bertrand, Senior Lecturer in Pharmaceutical Sciences, RMIT UniversityAmy Loughman, Postdoctoral Research Fellow, Deakin UniversityMelinda Jackson, Senior Research Fellow in the School of Health and Biomedical Sciences, RMIT UniversityLicensed as Creative Commons – attribution, no derivatives.