Is there a link between obesity and the types of bacteria in your gut?

Jeffrey I. Gordon, MD, of Washington University School of Medicine in St. Louis seems to think so.

Late last year, the journal, Nature, published results from his experiments comparing the gut bacteria of obese and skinny mice. The obese mice had a gene for obesity; the skinny mice didn’t.

The researchers found that obese mice had more “fat bacteria” that were able to extract more calories from food.

So if a fat mouse and a skinny mouse ate exactly the same meal, the fat mouse might get more calories from it. The calorie difference could add up significantly over time.

But as the obese mice lost weight, the proportion of their “fat bacteria” dropped. And another type of bacteria (like that found in skinny mice) became more abundant.

The same thing happened when another researcher in the group, Ruth Ley, PhD, studied 12 obese people.

As they lost weight over a year, their gut bacteria changed to look more like the skinny mice. It didn’t matter whether these obese patients were on a low-calorie, low-fat diet or a low-calorie, low-carb diet.

So do bacteria play a role in regulating weight?

When the researchers transplanted the “fat bacteria” into skinny mice, they started getting fat, too.

But the doctors aren’t sure what these findings mean or if they’ll play a major role in the fight against obesity.

The researchers caution against using antibiotics or probiotic pills to change your gut bacteria.

It would be dangerous because no one knows if you’ll gain or lose weight. Or what other results could occur.

The encouraging news seems to be that dieting can make a difference.

Not only will you lose weight, but your proportion of “fat bacteria” may fall, too. Which means you may absorb fewer calories from your meals as you lose weight.

As an explanation for the U.S. obesity epidemic, this seems a little too easy to me. Lifestyle changes must account for at least some of it.

But maybe this will be another factor.

What if something in our foods is causing a change in gut bacteria? Maybe the way cattle and other animals are routinely fed antibiotics is now impacting us. Or maybe genetically modified foods play a part.

It’ll be interesting to see if anything useful comes of this.