Feed your svelte bacteria
A few years ago, scientists led by Jeffrey Gordon, MD, of Washington University in St. Louis noticed that fat mice and skinny mice have very different gut microbes. Could certain bugs cause obesity? To find out, Dr. Gordon transferred gut bacteria called Firmicutes from obese mice into thin ones. The thin mice ate no more than they used to, but they quickly started packing on the pounds (OK, ounces). Firmicutes, it turns out, are really good at liberating calories from food, much better than the common gut bugs called Bacteroidetes.
Having more Firmicutes in your gut may allow you to absorb more of, say, the 1,200 calories in half a Domino’s bacon cheeseburger pizza than if you had more Bacteroidetes. “Some microbes change how efficiently we metabolize food,” says biologist Rob Knight of the University of Colorado, who studies the genetics of the microbiota, called the microbiome. This may explain why your friend can scarf down calories and remain slim, while you have merely to walk past a bakery to gain weight. “Obesity depends not just on calories ingested but also on the microbiome,” says Yang-Xin Fu, MD, of the University of Chicago Medicine. Like mice, heavy people tend to have more Firmicutes and fewer Bacteroidetes than slim people.
Another example: Certain gut bacteria produce a compound called PYY, which makes you feel full and reduces how much you eat. Absent those bacteria, your brain doesn’tget the “stop eating” signal. And H. pylori (of ulcer-causing fame) regulates the stomach’s production of ghrelin, an appetite-stimulating hormone. Several labs have found that people whose stomachs harbor more H. pylori have less ghrelin and thus less hunger; conversely, fewer H. pylori means more ghrelin and greater likelihood of overeating.
At this point, everyone asks, How can I get my slim friend’s menagerie of gut microbes? Scientists don’t know yet. But they have some clues. Bacteroidetes—the microbes linked to slimness—proliferate in the presence of fructans, compounds in asparagus, artichokes, garlic, and onions, notes microbiologist Andrew Gewirtz of Georgia State University. On the other hand, stress can decrease the abundance of Bacteroidetes, suggesting one more way stress may cause obesity.
Scientists are just starting to explore how to boost the growth of slimming gut bacteria using probiotic supplements and foods that fuel healthy bugs while zapping the fattening ones with other drugs. These ideas are in their earliest stages, so don’t go looking on your drugstore shelves for such products just yet.
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