Trust Your Gut

At Washington University in St. Louis, researchers have found that humans' ability to survive starvation may depend on the kinds of bacteria living in their guts. They deduced this by feeding poop and peanut butter to mice.

How about I back up a little.

If you haven't heard, the hot new field in biology is the "microbiome." There's even a Human Microbiome Project, started in 2008. It's reminiscent of the Human Genome Project, which pushed through the 1990s and early 2000s to complete a sequence of the human genome. But the microbiome isn't made of human DNA, or human anything. It's the collection of bacteria and other microorganisms that live inside us. And it's starting to seem pretty important.

Your microbiome is not an everyday cold or patch of infection. It's the Alamo. For every single cell in your body, there are 10 microbial cells. Yes, in your body. The only reason you look like a person and not a big oozing blob is that your cells are way bigger. Most of these microbes live in a thick layer in your intestines, where they help you digest certain foods but otherwise stay out of your business. In addition to the gut, your microbial companions (also called, rather romantically, your "flora") live in your various orifices and all over your skin.

Microbes first colonize humans at the moment of our birth. But our microbial populations can change over time: we eat things, touch things, get sick, take antibiotics. Scientists are just beginning to understand the relationship between our gut flora and our overall health. It's not a trivial relationship; we've evolved with this population as a part of our bodies.

The researchers in St. Louis are studying the role of gut bacteria in malnutrition. Specifically, they're looking at twins growing up near-starving in Malawi. Even though they have the same genes and eat the same food (what there is of it, anyway), the twins sometimes respond differently. One twin may develop kwashiorkor, the bloated-belly form of malnutrition that we see in photos from impoverished countries, while the other twin doesn't.

As ScienceNOW reports, the scientists wondered if different gut bacteria might be responsible for different responses to malnutrition. To test their theory, they took stool samples from a pair of twins like those described above. They fed the two stool samples to two groups of mice that had been carefully kept sterile since birth, in order to colonize the mice with the children's gut bacteria. Then they alternated between feeding the mice a typical Malawian diet (mostly corn flour) and a food used to treat malnutrition (which includes peanut butter).

The mice with the healthy twin's bacteria maintained a more stable weight, and a more stable population of gut flora, than the mice with the kwashiorkor twin's bacteria. Though this was just a pilot study, it suggests that gut bacteria may be crucial to humans' ability to survive starvation.

More applicable to most of us in the Western world was a 2009 study out of the same Washington University lab. Looking at gut microbes from obese and non-obese twins, the scientists found that the obese people had fewer types of bacteria in their guts. They also found that mothers and their children share a lot of their gut flora, regardless of whether the children are identical twins. This implies that our microbial makeup has much more to do with our environment than our genes.

In the future, doctors may use this kind of information to treat patients with microbial therapy--instead of drugs, why not put the right balance of bacteria into your body and let them do the work? Some doctors are already using so-called fecal transplants, which are exactly what they sound like. Is it gross? Yes. But pretty soon, we may have to get over it and admit that our microbes are looking out for us.