You Have A Hundred Trillion Friends Dear Reader, your body has about a trillion cells. But, you (and me) are only 10 percent human. For every human cell that is intrinsic to our body, there are about 10 resident microbes — including commensals (generally harmless freeloaders) and mutualists (favor traders) and, in only a tiny number of cases are those microbes pathogens (disease causing). And hear this: to the extent that we are bearers of genetic information (DNA), more than 99 percent of it is microbial. So actually we are actually walking talking ecosystems! Furthermore, this “second genome,” as it's sometimes called, exerts an influence on our health as great and possibly even greater than the genes we inherit from our parents. But while your inherited genes are more or less fixed, it may be possible to reshape, even cultivate, your second genome. What you put on your skin and what you eat are vastly more important than we ever thought. Consider that doing experiments with us humans is hard to get going from a legal standpoint, so we have to start with labratory mice. Even so, the implications are very interesting. For example: Some mice have been bred for low risk tolerance. Others for high risk tolerance. The breeders were proud of themselves for these two very different mice. Until researchers swapped the mice gut microflora (a technique called fecal transplantation). The risk takers became timid and the timid mice became risk takers. And this change happened within hours of the procedure. Genetics might have nothing to do with risk taking or timidity, and more to do with the types of microbes that live in a gut. For example: Some mice have been bred for obesity. Others to be lean. With no change in diet, and both groups eating the same mousey diet, fecal transplants made the obese mice lean and the lean mice obese. The change wasn't in hours like the risk taking results, but over the course of weeks. This experiment has had a modified first run in humans and researchers indicate similar results. It's looking like weight loss has a lot to do with who your tiny friends are: obese promoting microbes, or lean promoting microbes. And for those of you worried about your declining memory, here's an experiement that should pique your interest: Some mice have been bred without any microbiota - they're microbe free. Lets call this group of mice, the clean mice. Let's call the other group of mice, with normal/standard microbiota the dirty mice. The researchers had a small cage containing a plain napkin ring and an ornate napkin ring. Using a stop watch, they timed how long each mouse explored each object. Twenty minutes later they took the plain napkin ring out and replaced it with a star shaped cookie cutter. Once again they timed how long the mice explored the objects. The dirty mice remembered the ornate napkin ring and spent almost no time exploring it in favour of the cookie cutter. The clean mice on the other hand, had forgotten about their previous exposure to the ornate napkin ring, so they spent equal amounts of time on it and the cookie cutter. Somehow, the presence of gut microbes enabled memory - or the lack of gut microbes prevented short term memory. So the question is, without re-reading this paragraph, what was the new object introduced into the cage for the mice to explore? These are just a few of the experiments bringing health experts to reconsider our relationship to microbes. For more fascinating reading on this, and how all aspects of your health are affected, you could take a look at The Good Gut, by Justin and Erica Sonnenburg or Brain Maker by David Perlmutter.