Meet resistant starch—the carb that may help keep you trim.
Repeat after us: not all carbs are bad. Resistant starch is one of the good guys. It's a type of carbohydrate found in bananas (it's is even higher in green bananas), potatoes and whole-wheat pasta. Unlike simple carbs, like white bread, that break down into sugars in the small intestine, resistant starch "resists" digestion, staying intact until arriving at the large intestine. There, bacteria use it as fuel, releasing beneficial compounds (specifically, short-chain fatty acids) that may improve your gut microbiome and help keep you slim.
In a small study published in Nutrition & Metabolism, adults who ate 5 grams of resistant starch at breakfast boosted fat burning for the rest of the day. In larger doses, this carb may help us feel fuller longer and curb weight gain. Plus, since it isn't digested, it does not contribute calories to the foods it's in.
While researchers use both natural and man-made forms of this starch (which is commonly used in the large-dose studies), the form doesn't matter, says Guy Crosby, Ph.D., resistant-starch researcher and adjunct professor at Harvard's T.H. Chan School of Public Health. "The bacteria don't care as long as the nondigestible starch reaches the gut where they can convert it to short-chain fatty acids." He recommends aiming for about 10 grams per day. Most of us only get about 5.
As a general rule, starchy foods have more resistant starch when they're raw. Cooking breaks up the structure of starch, meaning it'll get digested before it reaches your large intestine. But letting cooked carbs cool gives starch a chance to return to its hardened state. For instance, a boiled potato has 1.3 grams of resistant starch, but studies show that cooked and cooled potatoes (like you'd find in a potato salad) can have 20 percent more.
A small, ripe banana has 4 g of resistant starch and green bananas have up to 80 percent more. Other sources include cooked pearled barley (4 g per cup, hot), pinto beans (3.6 g per cup, hot or cold), black beans (2 g per cup, hot or cold), pumpernickel bread (1 g per slice).