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It's Not Just Food That's Making You Gain Weight. It's This Surprising Reason, Too

What's inside of your gut could be responsible for making it bigger.

In the battle against the bulge, there's one crucially overlooked culprit: the changing composition of your gut bacteria.

A new study, published last October 2015 in the journal EBioMedicine, lends more evidence to the case against this newfound weight-loss crook. Wondering why the antipsychotic drug risperidone causes weight gain, researchers from the University of Iowa ran tests on mice—and found that the drug changed the rodents' population of bacterial freeloaders (increasing the number of some species, while wiping out the populations of others), and led to increasing weight gain...even when they ate the same amount of calories as mice who didn’t get risperidone.

The effect of this change in germ composition? "We conclude that excess weight gain in mice following risperidone treatment occurs through suppressed energy expenditure, attributable to an altered resting metabolic rate," the researchers write.

Sure, the studies were done on mice, but a growing body of research is zeroing in on the important role gut bacteria plays in regulating how much we gain (and lose) weight. Obesity researcher Jennifer Kuk, for example, says that our changing intestinal flora (because we now eat more meat than ever before) may be one reason why it's harder to shed the pounds now than it was in the '80s.


Meanwhile, at the Scientific American, Claudia Willis writes: "In studies of twins who were both lean or both obese, researchers found that the gut community in lean people was like a rain forest brimming with many species but that the community in obese people was less diverse—more like a nutrient-overloaded pond where relatively few species dominate."

From research conducted in the University of Washington in St. Louis and New York University, some scientists theorize that our gut germs help regulate the hunger-stimulating hormone ghrelin, as well as the way we store fat and keep our blood sugar in balance. 

So how do we make sure we keep up the variety of our gut bacteria? Try bacteria-rich fermented foods like kimchi, yogurt, or atsara, recommend nutritionists France Ruiz and Ross Baylon of St. Luke's Medical Center-Bonifacio Global City. "Mas improved ang metabolism, and they improve the natural microflora of the stomach," they explain.

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Also, avoid processed foods, writes Willis, as studies have shown that a diet high in these off-the-shelf goods leads to a lower variety of intestinal bacteria.

This story originally appeared on

* Minor edits have been made by the editors.