The microbes within us

Shorter thoughts are going to Twitter, but this will be the first in a series of longer posts of thoughts from #EB2013:

Bright and early on Saturday morning I attended the symposium "Managing the microbiome in human GI disease" put on by the American Society for Nutrition.  (The Experimental Biology meeting is made up of six societies: the American Society for Biochemistry and Molecular Biology (the reason for which I was ostensibly attending), the American Society for Nutrition, the American Society for Investigative Pathology, the American Society for Pharmacology and Experimental Therapeutics, the American Association of Anatomists, and the American Physiological Society.  These societies are themselves integrative and interdisciplinary, so any given symposium title could be difficult to assign to which society was sponsoring it.)

The emphasis of the symposium was on inflammatory bowel disease, but as an aside the speakers mentioned recent work on the relationship between obesity and the microbes inhabiting our guts.  For example, you can transfer the bacteria from a fat mouse to a lean mouse, and the lean mouse will gain weight (without changing how much it eats or its physical activity).

I was reminded of this later in the week when I met a graduate student who was researching obesity, but felt that she should move to some other disease for her postdoc, where she could contribute more to potential therapeutics and actually helping patients, since obesity is "preventable".

It got me to thinking about the way that we teach metabolism to the medical students.  We teach them that "calories in - calories out = weight gain", which is true: if you eat less and exercise more, you will lose weight.

But it's also true that for every human cell in your body, there are ten bacterial cells.  Most of these bacteria live in your gut, eating the same food you eat.  The calories they consume and expend are crucially important for how many calories are left available to you .  (The agricultural industry certainly appreciates this fact: they treat their livestock with low doses of antibiotics not to prevent bacterial infection, but to make them gain weight.)  As a society we tend to blame obese patients for making bad choices, but it's not like I chose what kinds of bacteria are living in my gut.

We're just beginning to learn about how specifically our gut bacteria contribute to our metabolism, so maybe that's why we don't want to include that when we teach metabolism.  We're not at the stage where we can tell people to eat certain brands of yogurt to solve certain medical problems (although I do know a scientist who believes he has cured his lactose intolerance by eating yogurt and colonizing his GI tract with the appropriate strains).  But we do know that our microbial communities are extremely important, and I think we're doing our students a disservice when we don't tell them that.