National Geographic
At first glance, you might think resistant starch is a handy way to eliminate wrinkles while ironing clothes. But it’s actually a type of carbohydrate—and a secret weapon for controlling your weight and preventing certain diseases.
Found in foods such as green bananas, raw potatoes, oats, certain nuts and seeds, beans and legumes, resistant starch doesn’t get digested in your small intestine like other starches; instead, it moves on and becomes fermented in your large intestine where it feeds beneficial bacteria that support various aspects of your health.
(Your gut microbiome affects the rest of your body. Here’s why.)
“Carbs get such a bad rap—resistant starch is another reason to get your carbs and choose them wisely,” says Tara Collingwood, a registered dietitian nutritionist based in Orlando.
Mounting evidence is shedding light on these health benefits. A February study published in Nature Metabolism found that consuming resistant starch for eight weeks facilitated weight loss among overweight adults by reshaping the gut microbiome, reducing systemic inflammation, improving insulin sensitivity, and inhibiting the body’s ability to absorb fat.
Other research has shown that resistant starch helps improve blood sugar control and reduces cancer risk along with premature mortality from any cause. Resistant starch has even been studied as a dietary therapy to limit the progression of diabetic kidney disease.
And yet, most adults in the U.S. are not consuming as much resistant starch as they should, according to a study in the Journal of Nutrition. Researchers found that most adults consume four to five grams of resistant starch a day, when “an adequate intake of resistant starch that confers health benefits is 15 grams per day,” says study coauthor Mindy A. Patterson, associate professor of nutrition and food sciences at Texas Woman’s University in Houston. “Most people aren’t getting enough because we eat a lot of processed foods in the U.S.”
Unripe bananas are a good source of type 2 resistant starch—which studies show has particular benefits for blood sugar, insulin resistance, bowel function, and inflammation.
Photograph by Photograph by Joe Petersburger, Nat Geo Image Collection
A colorized scanning electron micrograph of starch grains (green) within a plant’s cellulose cell wall compartments. The stored starch grains are called amyloplasts.
Micrograph by Dennis Kunkel Microscopy, Science Photo Library
Resistant starch vs. regular starch
The truth is: All dietary starches are carbohydrates. “Resistant starch has a name that says what it is—it resists digestion,” says Wendy Bazilian, a nutritionist and public health consultant based in San Diego and host of the podcast 1,000 Waking Minutes. “It’s not a new thing but it’s increasingly researched and becoming better understood.”
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When you consume regular starches, digestive enzymes in the small intestine immediately break down these carbs into glucose and they’re released into the bloodstream and absorbed by cells. “Most starches are broken down as energy and have no effect on the microbiome,” Collingwood says. Resistant starch has the clear advantage when it comes to blood sugar regulation and enhancing the microbiome.
What makes resistant starch so healthy is that after it passes through the upper digestive tract and arrives in the colon intact, resistant starch is fermented by bacteria in the colon. Thus, it acts as a prebiotic, serving as a food source for beneficial gut bacteria, such as bifidobacteria, which are also known as probiotics.
(What’s the difference between probiotics, prebiotics, and postbiotics?)
In the process, short-chain fatty acids (SCFAs), such as butyrate, are produced, and these SCFAs have positive influences on blood sugar regulation, cholesterol levels, immune function, and other aspects of your health, says Mary Ellen Camire, a professor of food science and human nutrition at the University of Maine.
Research has found that SCFAs work this magic by inhibiting harmful inflammation, promoting the breakdown of fats and other lipids, and stimulating the secretion of a hormone that indirectly regulates blood sugar levels by increasing the secretion of insulin.
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Resistant starch offers an added perk for people who are struggling to control their weight. Because resistant starches contain fewer calories (2.5 per gram) than regular starches (4 per gram) do, eating foods packed with resistant starch would lead to total lower calorie intake, which could help with weight loss.
Resistant starch also decreases concentrations of the hormone leptin, causing signals of fullness and satiety to kick in sooner, says Bazilian, which could contribute to consuming fewer calories throughout the day.
Different types of resistant starch
There are five types of resistant starch, each found in different foods—and each with different health benefits. “Not all resistant starches are created equal,” Patterson says.
Type 1 resistant starch is found in grains (such as quinoa and brown rice), seeds, beans, and some legumes, whereas type 2 resistant starch is present in green (unripe) bananas, raw potatoes, some legumes, and high amylose corn starch. Research suggests that consuming types 1 and 2, in particular, have positive effects on someone’s blood sugar response, insulin resistance, bowel function, and inflammatory markers.
(These foods can help you fight off everyday stress.)
Type 3 resistant starch is found in cooked and cooled potatoes, rice, pasta, and oats. The process of “cooking and cooling these starchy foods creates more resistant starch,” explains Camire. This is an instance where the more resistant starch a food contains, the healthier it is for you.
In a study in the Asia Pacific Journal of Clinical Nutrition, researchers compared the amount of resistant starch in freshly cooked white rice, cooked white rice that had been cooled for 10 hours, and cooked white rice that had been cooled and refrigerated for 24 hours then reheated: They found that the resistant starch content in the cooked-cooled-and-reheated rice was more than two and a half times higher than in the freshly cooked rice—and that consuming the reheated rice sparked a lower blood sugar response compared to the freshly cooked rice.
The finding is a strong argument in favor of eating your leftovers—but Camire adds that making potato salad, pasta salad, or rice salad is another good way to incorporate resistant starch into your diet.
By contrast, type 4 resistant starch is a chemically modified starch that doesn’t occur naturally, Patterson says. It’s often added to thicken soups, baked goods, and other manufactured foods. Research has found that consuming type 4 resistant starch in these foods is associated with a lower blood sugar and insulin response afterward. And type 5 resistant starches are created by combining starch and lipids (fatty compounds) to make them resistant to digestion; because they’re the newer kid on the block, less is known about the effects of type 5 resistant starches.
Tips for getting more resistant starch
Dietary supplements that contain resistant starch (in the form of potato flakes, for example) are increasingly populating the market. Some research suggests that they can be beneficial for intestinal health. But Patterson recommends relying on food first then “if you’re having a hard time increasing your intake, a supplement can augment a healthy diet.”
If you decide to try to increase your intake of resistant starch, do it slowly and gradually, Collingwood advises. “If you increase it by too much too soon, it can cause gas and bloating.”
If you ramp up your consumption gradually, most people tolerate resistant starch quite well. It’s worth a try, experts say, because adding more of this hidden ingredient is a great way to boost your gut health and your overall health.
Resistant starch “helps vindicate the evil characterization that some people place on carbs like potatoes or pasta,” Bazilian says. “If you can keep the gut healthy, everything else tends to operate better.”
