They live deep inside us. Right now, there are tens of trillions of them in your intestines, thousands of different species. If this sounds like an alien apocalypse, chill. Gut microbes are crucial for your health. They help digest food and boost your immune system. And, increasingly, science is learning their role in limiting body fat. What those bacterial armies do or don’t do in your guts is a factor in whether or not you have a gut.

GUT CHECK

Research is illuminating the role of our gut microbiome on body fat accumulation. One study looked at the data of 300,000 children, and determined that those who had been given antibiotics as infants had a 26% greater chance of developing obesity. Such drugs kill bacteria indiscriminately, including in the digestive system. Antacids also increased the obesity odds, though to a lesser degree, and combining antibiotics and antacids created the greatest risk of all.

In another study, researchers analyzed the bacteria in stool samples of 1760 female twins and surveyed self-reported diet questionnaires. They concluded that gut bacteria and diet both affect visceral fat gains. Furthermore, specific gut microbes may limit fat-gaining regardless of diet, and increasing them could reduce body fat.

HI, FIBER

Fecal transplantation (bacteriotherapy) is already a treatment for colitis, and recent and ongoing trials are investigating its efficacy for fat loss. But let’s go to the other end of the digestive tract—your mouth. The best way today of maintaining healthy, hard-working gut microbes is to feed them what they crave: fiber. In another study, mice fed a high-fat diet and no fermentable fiber plumped up fast, but adding a fiber supplement to the same diet dramatically reduced their plumping. You can take a fiber supplement, and you may need to if you’re on an ultra-low-carb diet, but most people just need to make a concerted effort to eat more fibrous foods. As an additional weight-loss benefit, fiber makes you feel full.

The Institute of Medicine recommends women consume at least 38 grams of fiber daily (30 grams if 50+) and men 25 grams (20 grams if 50+). Americans, in our over-processed era, only take in about 15 grams per day. Even a lot of healthy eaters skip over the fiber listings on labels. Don’t. Eat beans, lentils, nuts, seeds, whole grains, vegetables, and fruits. Keep your gut bacteria happy, and they’ll help keep your abs visible.