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April 30, 2018 | by  | in Opinion Super Science Trends |
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It’s What’s Inside That Counts

Your Homo sapiens sapiens body is part of a feedback loop responding to all kinds of biological, psychological, and cultural processes. These all have to be taken into account when trying to produce a better picture of how we work, both physically and mentally. But sometimes you just want an easy answer. We thought we had one in the bold new realm of the microbiome.

A microbiome is the genome, or total sum of genetic material, of all the microorganisms (or microbiota) on a human. Meaning, you are merely an upright lightning-powered meaty ecosystem for microorganisms, and like any ecosystem, you can be thrown off balance by any slight detrimental change. Microbiota are found in the nose, mouth, skin, and vagina, but the main ones of interest are the ones in the digestive tract, responsible for digesting your food and synthesising sugars and vitamins. The central nervous system communicates with your stomach’s nervous system through a pathway called the gut-brain axis. A hypothesis followed that detrimental changes to the microbiome, like the introduction of harmful bacteria, can have an effect on your mental health, contributing to anxiety and depression. To test this, the gut-brain axis had been expanded to include the microbiome, being rebranded as the “microbiome-gut-brain axis”.

Investigating how our personal germ zoos alter our behaviour opens up whole new paths of study, but so far, actually demonstrating their effect on human mental health is proving difficult, despite promising results.

For example, a series of studies on mice have shown that an infection with the nausea-inducing bacteria like Campylobacter causes them to have anxiety-like symptoms when faced with a maze puzzle. Testers were careful to ensure that the mice were infected in such a way that their anxiety symptoms are separate from the stress that would be caused by an immune response such as gut inflammation. These responses measured by the increased presence of the stress molecule corticosterone and other factors that indicated a brain chemistry associated with anxiety.

While this indicates that there is some kind of effect on mental well-being from gut bacteria, the difficulty in translating this to humans is that while we have similar gut-brain interactions to mice, we have completely different niches, metabolisms, and dietary demands, making the applicability of these studies to people tenuous at best. Lab mice are usually either bred or conditioned to have a certain health profile prior to testing to ensure accurate, trustworthy results, whereas humans can barely stick to one diet for a whole January, making human trials near impossible. While people with health conditions like irritable bowel syndrome often suffer acute stress, it can be difficult to discern where this is a result of the immune response or the overall health of the microbiota, or if one feeds into the other.

This doesn’t necessarily mean the end of the study, but with the media being what it is, the importance of the microbiome has been over exaggerated. Harvard professor William P. Hanage, in a piece for Nature, described the study of microbiomics as having “drowned in a tsunami of its own hype”, and encouraged scientists and science writers to exercise skepticism when talking about any all-encompassing effect on human well-being. Well, duly noted, sir.

So if I had to pass anything on, I’d remind people that science is less about leaping to conclusions and more about gesturing in the vague direction of one. And that the best seasoning for consuming any media about the microbiome is a grain of salt.

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