Oh sure, blame it on the bacteria!

Bacteria can cause other epidemics, why not obesity? Is there a relationship between our body weight and our bacterial inhabitants?

Two reports in Nature (1, 2) suggest that bacterial populations differ between people who are obese and people who not, and that the bacterial inhabitants of their guts, may be partly to blame.

In one study, the authors studied the bacterial populations of their volunteers' intestines by compiling a data set of 18,348 DNA sequences for bacterial 16S ribosomal RNA by sampling feces. Wow! That's a lot of ... well, I won't say it, but you know what I mean. In the other study, they looked the bacteria in mouse poop. If I were a lab technician at WSU, I know which study I would have preferred.

The results were pretty interesting. Lean people (and mice) had a higher ratio of one bacterial group (Bacteroidetes) to another (Firmicutes), than obese people (and mice). If obese people dieted, their ratios changed to become more like those found in lean people.


The question that comes to mind, is that maybe the populations of bacteria reflect what people are are feeding them. Maybe obese people eat different kinds of food than lean people.


But in one of the mouse studies, the researchers were able to raise mice in sterile environments, add different sorts of bacterial populations to the mice, and show that mice gained more weight when they got the population of bacteria from obese mice than they did when they were colonized with bacteria from lean mice.

I think the ideas put forth in the articles, that bacteria can breakdown food, that some bacterial species will be more efficient at doing so than others, and that bacterial populations can cause some people to use food more efficiently, are quite reasonable and really intriguing.

After all, bacteria make it possible for cows (and other ruminants) to live on grass. The bacteria break down the cellulose and the cows get the food. Humans also depend on bacterial metabolites for health. Bacteria make our vitamin K, which we need for blood clotting.

But, do our bacterial cohabitants really contribute to our weight?

I'm having this weird flashback to a moment in college when a friend told me that she had managed to repopulate her bowels with "good" bacteria after taking antibiotics. Unfortunately, I can instantly see all kind weird ways that the results of this study might be abused.

Nevertheless, the idea deserves further investigation.

1. Ley, R. et. al. "Microbial ecology: Human gut microbes associated with obesity" Nature 440
1022-1023 (21 December 2006).

2. Turnbaugh, et. al. "An obesity-associated gut microbiome with increased capacity for energy harvest" Nature 440 Nature 444, 1027-131 (21 December 2006).

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