It's Just a Gut Feeling

Two pieces of science news about.... well, guts last week that shook me up.

First, this bit on Boing Boing by my hero Maggie Koerth-Baker:

Do Bacteria Control Your Brain?

A new study [reported in Scientific American] 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.

From the Scientific American article:

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.

Adding bacteria to the guts of adult mice had no effect on their behavior, but if the intervention happened while the mouse was immature, they then exhibited normal mouse behavior. "This suggests that there is a critical period in the development of the brain when the bacteria are influential." The article then describes what genes and neurotransmitters appeared to have been affected.

Mix that with this piece from the New York Times, which tells of the recent discovery of "enterotypes" -- kind of like how human blood can be classified into types, but instead, a way of stratifying our gut bacteria ecosystems. After studying the flora of 400 people from a range of countries (and ages, health conditions, weights and genders), scientists have found that there are three enterotypes, each with different bacteria dominant.

This discovery is so new that no one knows what to do with it. Exploration needs to be extended to much larger populations, and to reach people who don't eat a Western or Japanese diet, for instance. Even so, I expect some astounding medical work to come out of it. And combined with the mouse study, it makes me wonder how long it will be before someone does a study correlating personality traits (like the big five) with the enterotypes.

And I also absorbed this astounding fact from the Times article: There are 10 trillion human cells in each of us -- but there are 100 trillion microbes. According to the Scientific American article, there are 30,000 human genes in each of us, but more than 3 million bacterial genes per person. So depending on which of those facts you emphasize, we're each only 10 percent human or 1 percent human.

Which makes me feel just a bit more complacent about our genes being 1 to 4 percent Neanderthal.