Too good to be true? Yes and no. Studies do show this nutrient may provide an array of health benefits. But as most experts point out, many of the claims demand more research. Experts also emphasize that RS is not a revolutionary discovery, but rather another piece of the complex nutritional puzzle. To sort out the facts from the hyperbole, we asked experts to help uncover what you should know about resistant starch.
What Is It?
To understand RS, you need a crash refresher course in carbohydrates. Many foods -- like fruits, vegetables, grains, legumes, and certain dairy products -- contain an assortment of carbs, including sugars, starches (RS falls here), and fiber, says Susan Bowerman, M.S., R.D., a lecturer in food science and nutrition at California Polytechnic State University in San Luis Obispo.
During digestion, most sugars and starches break down in the small intestine into glucose, which serves as our body's main source of energy. On the other hand, fiber -- both soluble (which partially dissolves in water) and insoluble (which remains intact) -- moves on to the large intestine undigested. Fiber is so important to your health because, as many large studies show, it helps reduce your risk of such conditions as constipation, heart disease, and diabetes.
On a molecular level, resistant starch is, indeed, a starch -- and should get burned as energy. But during digestion, RS actually mimics some of the properties of dietary fiber, "resisting" digestion and passing to the large intestine. As a result, some researchers call RS a third type of fiber.
More important, because RS has fiberlike properties, it offers many of the same health benefits. Similar to insoluble fiber, it helps prevent constipation by "increasing bulk and making elimination faster," says Janine Higgins, Ph.D., a professor at the University of Colorado who has extensively studied RS.
And like soluble fiber, RS ferments in the large intestine, lowering the pH level in the lower digestive tract. This makes the colon more acidic, says Bowerman, so it becomes less hospitable to bacteria that can cause illness. At the same time, a lower pH level helps healthy bacteria thrive, explains Higgins.
As important as digestive health may be, it doesnâ€™t cause much excitement. Utter the words "weight loss," however, and a crowd will gather. Enter RS, which appears to "inhibit certain enzymes responsible for the creation of fat and increase the amount of fat your body burns," says Hope Warshaw, R.D., author of "Diabetes Meal Planning Made Easy."
Following this discovery, reports emerged declaring that RS was the next great breakthrough for weight loss. Unfortunately, says Higgins, "there's no conclusive data to support that claim." Why RS may help with fat burning remains unclear. "It could be because when you eat resistant starch, you're not getting as many calories gram per gram as with regular starches," she suggests, "or it could be other reasons. We haven't nailed down the mechanisms for explaining that yet."
Bowerman adds that participants in the study were not obese but of normal weight. "It's hard to know if RS will do anything for overweight individuals," she says. Bottom line: No conclusive evidence exists yet to support RS consumption for weight loss.
Still other studies conclude that RS can help maintain even blood sugar levels. "This link has been well established," says Higgins. It may also improve insulin resistance in people with type 2 diabetes. "We could use more data on RS and insulin resistance," says Higgins, "but the studies conducted thus far have been excellent."
Focus on Fiber
For now, the most powerful benefit of RS remains its fiberlike qualities. "For the average person who doesn't get enough fiber, RS is a source we may not have thought about," says Bowerman. In reality, most Americans don't eat sufï¬cient amounts: Despite recommendations of 38 and 25 grams of fiber daily for men and women under 50, respectively, we typically consume 12 to 17 grams daily.
Unlike fiber, no recommended consumption levels exist yet for RS, in part because research findings are so new. However, Cynthia Harriman, director of food and nutrition strategies for Oldways, a nonprofit food and nutrition think tank, notes that "every bit of RS you eat counts toward your overall fiber needs." Higgins estimates that people would require from 5 to 30 grams daily to receive health benefits.
If you're intrigued enough to want to increase your intake of RS, start by consuming more legumes, suggests George Fahey, Jr., professor of animal and nutritional sciences at the University of Illinois, who has studied the health benefits of RS as well as analyzed the RS content of foods. Bananas make a good source of RS, too, but only when still slightly green. Harriman says cooked and cooled potatoes, pasta, and rice also contain RS.
In the end, nutritionists like Bowerman look at RS as more support for eating a nutrient-dense, whole-foods diet. "RS strengthens the argument that people should do their best to eat a wide variety of whole plant foods," she says, "since this ensures that we get the huge array of healthy compounds that nature intended."
How to Get More
Green banana: 1 medium, 4.7 grams
Navy beans:1/2 cup cooked, 3.8 grams
Lentils: 1/2 cup cooked, 3.4 grams
Split peas: 1/2 cup cooked, 3.1 grams
Kidney beans: 1/2 cup cooked, 2.4 grams
Black beans: 1/2 cup cooked, 2 grams
Pearl barley: 1/2 cup cooked, 1.9 grams
Brown rice: 1/2 cup cooked, 1.7 grams
Potato: 1 medium, boiled, then cooled, 1.3 grams
Whole-wheat pasta: 1 cup cooked, cold, 1.1 grams
White rice: 1/2 cup cooked, cold, .95 grams
Oatmeal: 1 cup cooked, .5 grams
Whole-grain bread: 2 slices, .5 grams
Corn: 1/2 cup cooked, .3 grams
*Amounts may vary depending on origin of food, how itâ€™s grown, etc.