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Gut feeling: how bacteria can mess with your mood

It’s not you, it’s the bacteria in your gut. Alaina Abplanalp Photography

Probiotics are something of a new dietary craze. Foods contain healthy “probiotic” bacteria, and these microbes can promote good gastrointestinal (GI) health.

But what about your brain? Apparently, bacteria influence what’s going on up there, too. Within the past several years, a blossoming field of study called “microbial endocrinology” has provided some provocative insights about the relationship between our GI microbiota and our mood and behaviour.

Studies in this field of have implicated GI microbes as a factor that can regulate the endocrine system. This could have both good and bad effects since the endocrine system is responsible for the production of hormones and coordinates metabolism, respiration, excretion, reproduction, sensory perception and immune function.

Consider the action of stress on the body. The endocrine system responds by sending out stress molecules called catecholamines that function as neurotransmitters and hormones. These molecules account for that fight-or-flight response that we feel when we encounter a stressful event. Conversely, there are molecules of the endocrine system that are deemed “feel good” molecules, such as dopamine, gamma-aminobutyric acid (GABA), oxytocin, endorphin and serotonin.

The implication is that, by influencing the endocrine system, GI microbiota could possibly influence our mood and behaviour by helping us “feel good” or enhancing our flight-or-flight reactions.

Most of what we know about this GI microbe-endocrine connection comes about due to an unusual side effect of irritable bowel syndrome (IBS). It is well documented that people suffering from IBS are more vulnerable to feelings of anxiety or depression or both. In fact, these psychological conditions can exacerbate IBS symptoms, indicating a reciprocal relationship between IBS and anxiety and depression.

One of the “feel good” molecules of the endocrine system, GABA, is a neurotransmitter that when low in abundance can lead to anxiety or depression. Two different GI bacteria, Lactobacillus and Bifidobacterium have been shown to produce GABA. Although it is unknown if GABA is playing a role in the resolution of symptoms, several studies have recently shown that supplements of either Lactobacillus or Bifidobacterium can relieve anxiety in both animals and humans suffering from IBS.

In other words, these bacteria have now become “psychobiotic”.

Another GI bacterium, Clostridium difficile is typically acquired during infancy. Usually harmless, this often antibiotic-resistant microbe can cause severe problems for older people on antibiotics, who subsequently succumb to diarrhoea’s or inflammation of the colon caused by C. difficile unrestrained in growth due to the lack of sufficient bacterial competition. C. difficile synthesises at least two toxins that interfere with neurons and possibly the endocrine system, as well. Intriguingly, patients with autism and schizophrenia have been shown to have higher than normal levels of this bacterial species.

Because of antibiotic resistance, one treatment that appears to have a good success rate is called a fecal transplant. This technique requires a healthy donor sample of fecal matter to be transplanted in the affected patient. While most of us might cringe at the thought, sufferers of C. difficile often feel they have little choice. Patients who have undergone the fecal transplant have described feeling better mere moments after the procedure is complete.

Combined, what these studies indicate is that an imbalance in the GI microbiota can manifest as both physiological and psychological pathologies. And it appears these pathologies may be resolved with the use of proper “psychobiotic” bacteria.

This article was first published on Real Clear Science.

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