Good news for carb lovers: There's reason not to shun carbohydrates—even some you may not think of as healthy.
That's because certain foods provide what's called resistant starch, or RS, which offers some of fiber's benefits.
"Resistant starch lowers blood sugar after a meal, helps reduce appetite, is anti-inflammatory, improves gut health, and may even help prevent colon cancer," says Jamie Kane, M.D., an assistant professor of medicine at Hofstra Northwell School of Medicine in New York.
Though researchers are still exploring some facets of resistant starch, there are many reasons to include it in your diet. Here's what we know, and how to incorporate it.
How Resistant Starch Helps You
One key action of resistant starch is that it helps keep your microbial balance healthy, providing a greater proportion of "good" to "bad" gut bacteria.
How? When you eat resistant starch, it passes undigested through the small intestine—where nutrients are absorbed—to the colon. There, it fuels the body's good bacteria.
And those healthy gut microbes, says Kane, play a role in almost every organ system in the body, including the gastrointestinal and immune.
"If you don't get enough fermentable fiber, like resistant starch, you risk the buildup of mucus-consuming bacteria that will degrade the protective lining of your intestines, allowing pathogens to gain access," explains Michael Keenan, Ph.D., a professor of nutrition and food sciences at Louisiana State University.
A thinner-than-optimal mucus layer might make you more susceptible to inflammatory bowel disease and colon cancer, for example.
In addition, blood sugar (glucose) levels rise more slowly after meals with resistant starch, which helps the body better use the hormone insulin. This may improve type 2 diabetes control and weight management.
The starch might even increase fat burning. According to a small study published in the journal Nutrition & Metabolism, people burned 23 percent more fat after a meal with 5 percent resistant starch than they usually did after a meal without it.
Where to Get Resistant Starch
One type of resistant starch—there are five types—is found in whole grains and seeds, another in certain legumes (chickpeas, kidney beans, lentils) and underripe bananas.
In fact, green bananas are the best source of resistant starch. (The starch turns to sugars as the fruit ripens.)
Unprocessed foods are generally the healthiest way to get resistant starch, but there are exceptions. Pasta, potatoes, and white rice are good sources of the type of resistant starch that forms when foods are cooked, then cooled—a process that alters the chemical structure of the carbs in these foods.
Eating them cold or at room temperature can be appetizing, too: Think pasta or potato salad.
How much resistant starch should you get? You need to consume 25 to 30 grams of fiber per day, but there's no such recommendation for resistant starch.
"We don't really know how much we need because we don't even really know how to measure it properly," says Diane Birt, Ph.D., distinguished professor of food science and human nutrition at Iowa State University.
The best way to get enough to reap its benefits is to increase your fiber intake, and to eat foods that contain it.
What about resistant starch supplements (notably from potato starch)? "It's hard to get too much of a nutrient when you get it in food," Birt says. "But with supplements we don't know how much is too much, and they may interfere with absorption and bioavailability of other nutrients."
And when you get resistant starch from foods, you get many other vitamins, minerals, and health-promoting compounds along with it. Plus, some evidence suggests that the other fiber in foods works along with resistant starch in beneficial ways.
Editor's Note: This article also appeared in the November 2017 issue of Consumer Reports on Health.