A new study has found evidence suggesting that you are not what you eat, so much as you are what's living in your gut. In mice, at least, the presence of normal gut bacteria has a significant impact on how an individual mouse behaves, and how its brain develops.
this new study is the first to extensively evaluate the influence of gut bacteria on the biochemistry and development of the brain. The scientists raised mice lacking normal gut microflora, then compared their behavior, brain chemistry and brain development to mice having normal gut bacteria. The microbe-free animals were more active and, in specific behavioral tests, were less anxious than microbe-colonized mice.
In one test of anxiety, animals were given the choice of staying in the relative safety of a dark box, or of venturing into a lighted box. Bacteria-free animals spent significantly more time in the light box than their bacterially colonized littermates. Similarly, in another test of anxiety, animals were given the choice of venturing out on an elevated and unprotected bar to explore their environment, or remain in the relative safety of a similar bar protected by enclosing walls. Once again, the microbe-free animals proved themselves bolder than their colonized kin ...
Consistent with these behavioral findings, two genes implicated in anxiety -- nerve growth factor-inducible clone A (NGF1-A) and brain-derived neurotrophic factor (BDNF) -- were found to be down-regulated in multiple brain regions in the germ-free animals ...
When Pettersson's team performed a comprehensive gene expression analysis of five different brain regions, they found nearly 40 genes that were affected by the presence of gut bacteria. Not only were these primitive microbes able to influence signaling between nerve cells while sequestered far away in the gut, they had the astonishing ability to influence whether brain cells turn on or off specific genes.
Personally, I'd like to see more analysis on what these findings mean. The Scientific American story quoted above makes it sound like normal gut bacteria are, on the whole, kind of cramping the brain's style. Given the evidence that exists about healthy gut bacteria's importance to maintaining other aspects of physical health, I'm curious whether this study implies that we humans have accepted a bit of a trade off. We get gut bacteria that help us digest food and train our immune systems—but we loose some control over how our brains function, possibly to our detriment, but possibly not, depending on the circumstances.
Oh, and, before the rest of you get a chance, I'm going to jump in here and make the obvious comment: "I, for one, welcome our new E. coli overlords."
Scientific American: The Neuroscience of the Gut
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