tag:theconversation.com,2011:/africa/topics/cell-metabolism-8867/articlesCell Metabolism – The Conversation2023-03-29T12:28:19Ztag:theconversation.com,2011:article/2011492023-03-29T12:28:19Z2023-03-29T12:28:19ZBrains also have supply chain issues – blood flows where it can, and neurons must make do with what they get<figure><img src="https://images.theconversation.com/files/516713/original/file-20230321-20-at1818.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C1921%2C1561&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Blood carries oxygen and vital nutrients to the brain.
</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/cerebral-angiography-image-from-fluoroscopy-in-royalty-free-image/1473413961">Mr. Suphachai Praserdumrongchai/iStock via Getty Images</a></span></figcaption></figure><p><a href="https://doi.org/10.3389/fnint.2022.818685">Neuroscientists have long assumed</a> that neurons are greedy, hungry units that demand more energy when they become more active, and the circulatory system complies by providing as much blood as they require to fuel their activity. Indeed, as neuronal activity increases in response to a task, blood flow to that part of the brain increases even more than its rate of energy use, leading to a surplus. This increase is the basis of common <a href="https://doi.org/10.3389/fnint.2022.818685">functional imaging technology</a> that generates colored maps of brain activity.</p>
<p>Scientists used to interpret this apparent mismatch in blood flow and energy demand as evidence that there is no shortage of blood supply to the brain. The idea of a nonlimited supply was based on the observation that <a href="https://doi.org/10.1038%2Fjcbfm.2013.181">only about 40% of the oxygen</a> delivered to each part of the brain is used – and this percentage actually drops as parts of the brain become more active. It seemed to make evolutionary sense: The brain would have evolved this faster-than-needed increase in blood flow as a safety feature that guarantees sufficient oxygen delivery at all times.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/B10pc0Kizsc?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Functional magnetic resonance imaging is one of several ways to measure the brain.</span></figcaption>
</figure>
<p>But does blood distribution in the brain actually support a demand-based system? <a href="https://scholar.google.com.br/citations?user=cldyZo8AAAAJ&hl=en">As a neuroscientist myself</a>, I had previously examined a number of other assumptions about the most basic facts about brains and found that they didn’t pan out. To name a few: Human brains <a href="https://doi.org/10.1002/cne.21974">don’t have 100 billion neurons</a>, though they do <a href="https://doi.org/10.3389/fnana.2014.00046">have the most cortical neurons</a> of any species; the <a href="https://doi.org/10.1126/science.aaa9101">degree of folding of the cerebral cortex</a> does not indicate how many neurons are present; and it’s not larger animals that live longer, but <a href="https://doi.org/10.1002/cne.24564">those with more neurons in their cortex</a>.</p>
<p>I believe that figuring out what determines blood supply to the brain is essential to understanding how brains work in health and disease. It’s like how cities need to figure out whether the current electrical grid will be enough to support a future population increase. Brains, like cities, only work if they have enough energy supplied.</p>
<h2>Resources as highways or rivers</h2>
<p>But how could I test whether blood flow to the brain is truly demand-based? My freezers were stocked with preserved, dead brains. How do you study energy use in a brain that is not using energy anymore?</p>
<p>Luckily, the brain leaves behind evidence of its energy use through the pattern of the vessels that distribute blood throughout it. I figured I could look at the <a href="https://doi.org/10.3389/fnint.2022.760887">density of capillaries</a> – the thin, one-cell-wide vessels that transfer gases, glucose and metabolites between brain and blood. These capillary networks would be preserved in the brains in my freezers.</p>
<p>A demand-based brain should be comparable to a road system. If arteries and veins are the major highways that carry goods to the town of specific parts of the brain, capillaries are akin to the neighborhood streets that actually deliver goods to their final users: individual neurons and the cells that work with them. Streets and highways are built on demand, and a road map shows what a demand-based system looks like: Roads are often concentrated in parts of the country where there are more people – the energy-guzzling units of society.</p>
<p>In contrast, a supply-limited brain should look like the river beds of a country, which couldn’t care less about where people are located. Water will flow where it can, and cities just have to adjust and make do with what they can get. Chances are, cities will form in the vicinity of the main arteries – but absent major, purposeful remodeling, their growth and activities are limited by how much water is available.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Microscopy image of astrocytes contacting a capillary" src="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516731/original/file-20230321-2166-um4qs4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">This image shows astrocytes, a type of brain cell, contacting a ravinelike capillary.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/astrocyte-in-the-brain-touching-a-capillary-250x-royalty-free-image/152883277">Ed Reschke/Stone via Getty Images</a></span>
</figcaption>
</figure>
<p>Would I find that capillaries are concentrated in parts of the brain with more neurons and supposedly require more energy, like streets and highways built in a demand-based manner? Or would I find that they are more like creeks and streams that permeate the land where they can, oblivious to where the most people are, in a supply-driven manner?</p>
<p>What I found was clear evidence for the latter. For <a href="https://doi.org/10.3389/fnint.2022.760887">both mice</a> <a href="https://doi.org/10.3389/fnint.2022.821850">and rats</a>, capillary density makes up a meager 2% to 4% of brain volume, regardless of how many neurons or synapses are present. Blood flows in the brain like water down rivers: where it can, not where it is needed.</p>
<p>If blood flows regardless of need, this implies that the brain actually uses blood as it is supplied. We found that the tiny variations in capillary density across different parts of dead rat brains matched perfectly with the rates of blood flow and energy use in the same parts of other living rat brains that researchers measured 15 years prior. </p>
<h2>Resolving blood flow and energy demand</h2>
<p>Could the specific density of capillaries in each part of the brain be so limiting that it dictates how much energy that part uses? And would that apply to the brain as a whole?</p>
<p>I partnered with my colleague <a href="https://scholar.google.com/citations?user=18-0e2EAAAAJ&hl=en">Doug Rothman</a> to answer these questions. Together, we discovered that not only do both human and rat brains do what they can with what blood they get and typically work at about 85% capacity, but overall brain activity is indeed <a href="https://doi.org/10.3389/fnint.2022.818685">dictated by capillary density</a>, all else being equal. </p>
<p>The reason why only 40% of the oxygen supplied to the brain actually gets used is because this is the maximum amount that can be exchanged as blood flows by – like workers trying to pick up items on an assembly line going too fast. Local arteries can deliver more blood to neurons if they start using slightly more oxygen, but this comes at the cost of diverting blood away from other parts of the brain. Since gas exchange was already near full capacity to begin with, the fraction of oxygen extraction seems to even drop with a slight increase in delivery.</p>
<p>From afar, energy use in the brain may look demand-based – but it really is supply-limited.</p>
<h2>Blood supply influences brain activity</h2>
<p>So why does any of this matter?</p>
<p>Our findings offer a possible explanation for why the brain can’t truly multitask – only quickly alternate between focuses. Because blood flow to the entire brain is tightly regulated and remains essentially constant throughout the day as you alternate between activities, our research suggests that any part of the brain that experiences an increase in activity – because you start doing math or playing a song, for example – can only get slightly more blood flow at the expense of diverting blood flow from other parts of the brain. Thus, the <a href="https://doi.org/10.1126/science.1183614">inability to do two things at the same time</a> might have its origins in blood flow to the brain being supply-limited, not demand-based. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="MRI brain scan images" src="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=727&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=727&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=727&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=914&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=914&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516735/original/file-20230321-2077-i19xsb.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=914&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A better understanding of how the brain works could offer insights into human behavior and disease.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/brain-scan-close-up-royalty-free-image/sb10069835m-001">Peter Dazeley/The Image Bank via Getty Images</a></span>
</figcaption>
</figure>
<p>Our findings also offer insight into aging. If neurons must make do with what energy they can get from a mostly constant blood supply, then the parts of the brain with the highest densities of neurons will be the first to be affected when there is a shortage – just like the largest cities feel the pain of a drought before smaller ones. </p>
<p>In the cortex, the parts with the <a href="https://doi.org/10.3389/fnint.2022.821850">highest neuron densities</a> are the hippocampus and entorhinal cortex. These areas are involved in short-term memory and the <a href="https://doi.org/10.1212%2F01.wnl.0000106462.72282.90">first to suffer in aging</a>. More research is needed to test whether the parts of the brain most vulnerable to aging and disease are the ones with the greatest number of neurons packed together and competing for a limited blood supply. </p>
<p>If it’s true that capillaries, like neurons, <a href="https://doi.org/10.1016/j.cmet.2019.05.010">last a lifetime</a> in humans as they do in lab mice, then they may play a bigger role in brain health than expected. To make sure your brain neurons remain healthy in old age, taking care of the capillaries that keep them supplied with blood may be a good bet. The good news is that there are two proven ways to do this: a <a href="https://doi.org/10.1001/archneurol.2011.548">healthy diet</a> and <a href="https://doi.org/10.18632/aging.103046">exercise</a>, which are never too late to begin.</p><img src="https://counter.theconversation.com/content/201149/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suzana Herculano-Houzel does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Neuroscientists have typically thought of energy supply to the brain as demand-based. A supply-limited view offers another perspective toward aging and why multitasking can be difficult.Suzana Herculano-Houzel, Associate Professor of Psychology, Vanderbilt UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/954282018-04-24T09:04:43Z2018-04-24T09:04:43ZYes, your kids can run all day – they’ve got muscles like endurance athletes<figure><img src="https://images.theconversation.com/files/215881/original/file-20180423-75090-1dllwag.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tired from parenting? Blame your muscles. </span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/father-son-on-coast-engaged-sports-789769963?src=bx52mPj2TwYs5GH2SJyz9w-4-23">from www.shutterstock.com </a></span></figcaption></figure><p>Most of us know children who can run and play for hours and hours, taking only short rests. </p>
<p>As a parent or carer, it can be exhausting. For scientists, why this is the case has long been the source of debate – is it due to fitness? Or something else? </p>
<p>Our <a href="https://www.frontiersin.org/articles/10.3389/fphys.2018.00387/abstract">study published today</a> looked at performance and recovery of children and adults doing strenuous cycling. It shows children not only out-perform most adults, but can perform as well as highly-trained adult endurance athletes, and then recover even faster afterwards.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/health-check-is-there-an-optimal-time-of-day-to-work-out-87181">Health Check: is there an optimal time of day to work out?</a>
</strong>
</em>
</p>
<hr>
<h2>Children’s muscles are different</h2>
<p>Repeated experiments have shown that the muscles of children tend to fatigue <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/mus.880150323">more slowly than adults</a></p>
<p>These results seem to fly in the face of what science would predict. For example, children have shorter limbs, so they have to take more steps and should therefore theoretically use more energy. </p>
<p>Children are also less able to make use of tendon energy return systems – that is, they store less energy in their tendons so they can’t reuse this energy to propel themselves during <a href="http://jeb.biologists.org/content/220/7/1287">movement</a>. </p>
<p>And children show greater activity in muscles that oppose or control movement, a reflection of the fact that typically they are less skillful, and therefore use more <a href="https://www.sciencedirect.com/science/article/pii/S1050641197846263">energy</a>.</p>
<p>So how do their muscles stay fresh? </p>
<h2>Aerobic and anaerobic exercise</h2>
<p>One possible explanation for the remarkable muscle endurance of children could be their different use of energy <a href="https://link.springer.com/article/10.1007/s40279-016-0671-1">pathways</a>. </p>
<p>Anaerobic (“oxygen-independent”) pathways produce large amounts of energy without the need for oxygen - but tend to cause rapid fatigue. For example, sprinters rely on anaerobic metabolism to run fast over short distances. </p>
<p>Aerobic (“oxygen-dependent”) pathways tend to produce energy at a slower rate but allow us to work for many hours without muscle shut down, like in a well-run marathon. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/the-science-of-elite-long-distance-running-94490">The science of elite long distance running</a>
</strong>
</em>
</p>
<hr>
<p>We know from existing research that children seem to be able to get more of their energy from aerobic pathways than adults, minimising the <a href="https://www.thieme-connect.com/DOI/DOI?10.1055/s-2008-1025820">fatiguing anaerobic contribution</a>. Their aerobic machinery also kicks into gear faster than adults, so they don’t need to rely as much on anaerobic metabolism when exercise first <a href="https://www.tandfonline.com/doi/abs/10.1080/026404102753576099">starts</a>. </p>
<p>These benefits are believed to partly result from children having a greater proportion of so-called “slow-twitch” muscle fibres, which have a greater activity of important enzymes that drive release of energy from aerobic <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/mus.880150323">pathways</a>.</p>
<p>Such findings prompted us to speculate that children’s muscles might actually respond to exercise in a similar way to adult endurance athletes, since they too show these <a href="https://link.springer.com/article/10.1007/s40279-016-0671-1">characteristics</a>. </p>
<h2>Let’s go cycling</h2>
<p>We tested our speculation in a study run by researchers at <a href="https://www.frontiersin.org/articles/10.3389/fphys.2018.00387/abstract">Université Clermont Auvergne, in France</a>. </p>
<p>Children (average age 10.5 years), young adults (21.2 years) with a similar physical activity level as the children, and age- and height-matched endurance-trained male athletes (21.5 years) were asked to complete two cycling tests on a stationary bicycle. </p>
<p>In the first test, power output was continually increased until exhaustion. In the second test, the subject completed a 30-second all-out cycle sprint. These tests allowed us to measure numerous physiological responses to exercise, and to assess both the rate of fatigue and then recovery specifically during brief, maximal-intensity exercise.</p>
<p>We found that the children fatigued as much in the all-out cycle as the endurance-trained athletes (about 40% loss of power), and much less than the untrained adults (about 50% loss).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/216031/original/file-20180423-94118-1kucp99.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"></a>
<figcaption>
<span class="caption">Children recover faster than adults from intense bursts of cycling.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/young-children-bikes-scooters-park-290589275?src=GTrVTDPyOTvEwdW4XcPVFw-1-27">from www.shutterstock.com</a></span>
</figcaption>
</figure>
<p>Data also show that the proportion of energy derived from aerobic pathways in the 30-second cycle sprint was similar in the children and athletes, and more than in untrained adults.</p>
<p>These results clearly show that fatigue rates in response to high-intensity exercise may be the same in children as they are in highly-trained adult endurance athletes, and that this is associated with an incredible generation of energy from aerobic energy pathways.</p>
<p>But data collected during recovery from the exercise also revealed startling outcomes. The rate at which oxygen use declined after the exercise was the same in children and athletes. The rates at which heart rate returned to normal and lactate (a compound associated with muscle fatigue) cleared from the blood were even faster in the children, and again much faster than in untrained adults. </p>
<p>These data show that children’s muscles recover rapidly from high-intensity exercise, and possibly reveal why children are able to produce repeated exercise efforts when most of us adults continue to feel exhausted.</p>
<h2>How children’s muscles work</h2>
<p>Such data provide strong hints as to how to optimise exercise and sporting performance in children. </p>
<p>Children might benefit from short, high-intensity exercise bouts to boost anaerobic capacity, and a focus on movement skill, muscular strength, and other physical attributes more than in adults. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/health-check-why-do-we-get-muscle-cramps-93493">Health check: why do we get muscle cramps?</a>
</strong>
</em>
</p>
<hr>
<p>Adults (and adolescents), on the other hand, may need to place a greater emphasis on improving their muscle aerobic capacity. </p>
<p>There may also be important health implications. Metabolic diseases, including <a href="https://academic.oup.com/jcem/article/94/12/4923/2596917">diabetes</a> and many forms of <a href="http://www.cancernetwork.com/oncology-journal/chronic-inflammation-and-cancer-role-mitochondria">cancer</a>, are increasing in prevalence in adolescents and younger adults but are still rarely seen in <a href="https://www.canada.ca/en/public-health/services/chronic-diseases/reports-publications/diabetes/diabetes-canada-facts-figures-a-public-health-perspective/chapter-1.html">children</a>. </p>
<p>It might be the case that the loss of muscle aerobic capacity between childhood and early adulthood is a key maturation step that allows metabolic diseases to take hold. </p>
<p>It will be interesting in future to examine the link between muscle maturation and disease, and test whether the maintenance of our childhood muscles through exercise training might be the best medicine to prevent disease.</p>
<p>Either way, at least we now have some idea as to why children are able to play, and play, and play, when we adults need to take a break. Kids are already elite.</p><img src="https://counter.theconversation.com/content/95428/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Children’s muscles recover rapidly from high-intensity exercise, and kids can produce repeated exercise efforts when most of us adults continue to feel exhausted.Anthony Blazevich, Professor of Biomechanics, Edith Cowan UniversitySébastien Ratel, Maître de Conférences en physiologie de l'exercice, Université Clermont Auvergne (UCA)Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/226622014-02-05T15:56:06Z2014-02-05T15:56:06ZShivering unlocks new way of fighting fat<figure><img src="https://images.theconversation.com/files/40669/original/ynxscfvy-1391533912.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Shiver me timbers.</span> <span class="attribution"><span class="source">bmhkim</span></span></figcaption></figure><p>Shivering is not an activity many of us enjoy. We do it because we are cold and uncomfortable. But perhaps the news that it could have some of the same benefits as moderate bouts of exercise will stop us running in from the cold so quickly. Researchers have found that the act of shivering can stimulate the conversion of energy-storing “white fat” into energy-burning “brown fat”. </p>
<p>The findings, published in <a href="http://www.cell.com/cell-metabolism/retrieve/pii/S1550413114000060">Cell Metabolism</a>, show that when humans shiver their levels of hormones irisin (produced by muscle) and FGF21 (produced by brown fat) increase. Specifically, around 10-15 minutes of shivering by volunteers placed in temperatures of less than 15°C resulted in equivalent rises in irisin as an hour of moderate exercise.</p>
<p>Irisin, identified just <a href="http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10777.html">two years ago</a> in animals, converts white fat into brown fat. Unlike white fat, brown fat is designed to produce heat by burning calories. For example, around 50g of white fat retains more than 300 kilocalories of energy in the body. The same amount of brown fat could burn up to 300 kilocalories a day.</p>
<p>There has been a lot of excitement surrounding the discovery of irisin because the energy-burning nature of brown fat makes it a potential therapeutic tool for targeting obesity and diabetes. It appears to be a golden ticket to promoting a healthy metabolism: as well as burning calories, it drains the blood of glucose (useful for preventing the onset of type II diabetes) as well as draining blood of unhealthy fat like triglycerides.</p>
<p>Also through studies in the laboratory on animals, FGF21 has been found to be a powerful activator of this brown fat, energy burning process. It is a molecule that originates in the liver and in brown fat itself. Since brown fat was discovered in humans, researchers have been bent on <a href="http://www.bbc.co.uk/news/health-18996076">working out</a> how to stimulate more of it, which makes this new research particularly exciting.</p>
<h2>Unlocking our brown fat potential</h2>
<p>The capacity of brown fat to burn calories in order to produce heat and maintain body temperature in cold environments has long been known in animals. We are all born with supplies of brown fat; it is nature’s way of preventing hypothermia in babies. But <a href="http://ajpendo.physiology.org/content/293/2/E444">until recently</a>, it was thought to vanish in early infancy, getting replaced by “bad” white fat that sits on our waistlines. </p>
<p>We now know that brown fat is present in most, if not all, adults. Those with more brown fat are slimmer than those without. Glucose levels are also lower in humans with more brown fat. Efforts are therefore being made into understanding how brown fat is stimulated in humans. Previous studies have shown how irisin activates it in rodents; this research is an important step in understanding how it is stimulated in humans. </p>
<p>It was already known that cold temperatures stimulate brown fat, but a comprehensive knowledge on how the body signals that message to its cells was lacking. This latest study set out to better understand the mechanism underlying the activation of brown fat. </p>
<p>When we are cold, we first activate our brown fat because it burns energy and releases heat to protect us. When that energy is insufficient, our muscles contract mechanically, or shiver, thereby generating heat. But we did not know how muscle and fat communicate in this process. For the first time, this research shows the way that they communicate with each other through specific hormones – turning white fat cells into brown fat cells to protect us from the cold.</p>
<p>The identification of these two molecules, irisin and FGF21, as capable of promoting energy expenditure in humans, opens prospects for being used for potential drug developments. There is nothing better than promoting exercise as a healthy habit to enhance muscle production of irisin that will impair accumulation of calories as fat in our body. But, when exercising is difficult for clinical or personal conditions, knowing that enhancing certain hormones in the blood may promote energy expenditure could help develop more tools to combat obesity.</p><img src="https://counter.theconversation.com/content/22662/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Francesc Villarroya receives funding from Generalitat de Catalunya, MINECO (Spain) and European Union. He is affiliated with University of Barcelona and CIBERobn..</span></em></p>Shivering is not an activity many of us enjoy. We do it because we are cold and uncomfortable. But perhaps the news that it could have some of the same benefits as moderate bouts of exercise will stop…Francesc Villarroya, Professor, Department of Biochemistry and Molecular Biology, Universitat de BarcelonaLicensed as Creative Commons – attribution, no derivatives.