When you hear the word "starch," what comes to mind? Most likely, you're thinking "blood sugar spikes," "empty calories," or even "gluten." Resistant starch (RS), however, can't be digested. Found in many common foods such as potatoes, legumes, cashews, raw oats, and green bananas, resistant starch passes through the stomach and small intestine largely undigested, moving into the colon where it "feeds" healthy gut bacteria. Most starch is broken down by digestive enzymes and absorbed as glucose. But RS is the exception.
Resistant starch has other important functions in the gut. When beneficial bacteria feed on it, several byproducts are formed, most notably butyrate, a short-chain fatty acid that protects against colon cancer by inhibiting DNA damage and blocking tumor growth. Butyrate also provides energy for the rapidly and constantly growing cells lining the colon-without it, colon cells can die. Additionally, RS reduces acidity in the colon, preventing inflammation and potentially protecting against colon cancer.
Resistant starch is also extremely effective at improving insulin sensitivity and reducing blood glucose levels; some studies show resistant starch can prevent blood sugar spikes for several hours, even after a second meal. In one study, people who consumed 15-30 grams of resistant starch per day showed a 33-50 percent improvement in insulin sensitivity after four weeks.
Other benefits of resistant starch:
- Better absorption of minerals, including calcium and magnesium, and enhanced production of biotin, folic acid, and vitamin K in the gut.
- Reduced absorption of toxins and potential carcinogens in the intestines.
- Lower blood cholesterol and triglyceride levels.
- Increased feelings of satiety, enhanced weight loss, and a reduction in the number of calories consumed.
Types of RS
There are four different kinds of RS:
- Type 1. Grains, seeds, nuts, beans, and lentils contain starch that's bound within the cell walls of the plant. It's inaccessible to the body and "resists" digestion. Note: Wheat is a source of RS, so avoid if following a gluten-free diet.
- Type 2. A form of RS found in green bananas, raw potatoes, and plantains-not always a practical source for daily consumption. Cooking these foods converts the RS to regular starch, removing the benefits.
- Type 3. This type is created when Type 1 or Type 2 foods are cooked and then cooled. The process of cooling converts some of the digestible starches back into resistant starches. So a boiled, then chilled, potato will have more resistant starch than a hot baked potato. The same goes for beans-cooked and then cooled, they're higher in resistant starch.
- Type 4. These are synthetic, commercially manufactured resistant starches (for example, hi-maize resistant starch) that don't occur naturally.
Most experts suggest getting 15-20 grams of RS per day. You can easily add more RS to your diet with a few simple tips:
- Eat cold beans. Cooking and then cooling beans enhances the RS content. Add them to salads, or toss into stir-fry dishes and gently warm.
- Avoid ripe bananas. Under-ripe versions have a higher RS content. Skip the soft ones with brown splotches, and choose firm, pale yellow ones with some green at the tips and ends. Eat them as is, or add to smoothies.
- Add potato starch to smoothies. Raw potato starch (not potato flour) is an easy way to boost daily RS intake. It contains 8 grams of resistant starch per tablespoon. Add it to smoothies, or mix a tablespoon in a glass of water.
- Chill your taters. Chilling increases the amount of RS. Toss cooked and cooled potatoes with olive oil and basil; add cubes to soups just before serving; or make potato salad (see recipe link below).
- Eat sushi. The RS in rice also develops after it's cooked and then cooled. Spread cooked rice on a sheet of nori, then layer on avocado, carrot strips, bean sprouts, and cucumbers. Cook your sushi rice with vinegar, which helps the RS conversion.