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This special kind of starch that “resists” digestion has several health benefits and can be part of a blood-sugar-friendly diet.

What is resistant starch and how does it impact glucose?

This special kind of starch that “resists” digestion has several health benefits and can be part of a blood-sugar-friendly diet.

Ashley Welch
WRITTEN BY
Ashley Welch
Stephanie Greunke, RD
REVIEWED BY
Stephanie Greunke, RD
UPDATED: 10/05/2023
PUBLISHED: 03/15/2021
🕗 6 MINUTE READ
ARTICLE HIGHLIGHTS
Resistant starch is a type of starch that resists digestion, so it does not raise blood sugar as much as other starches.
There are five types of resistant starch, found naturally in foods like oats and bananas or created by cooking and then cooling starchy foods.
Eating resistant starch improves insulin sensitivity and promotes good gut bacteria that produce compounds that enhance metabolic health.
Research shows intake of 15-60 grams of resistant starch per day can lower insulin levels after meals and increase insulin sensitivity over time.
People can add more resistant starch to their diets by eating unripe bananas, oatmeal, and legumes or by cooking and cooling starchy foods like rice or potatoes.

Eating fewer starchy foods like potatoes, bread, and rice is conventional wisdom for people trying to lose weight or optimize their glucose levels. That’s because starch is a carbohydrate that consists of numerous glucose units joined by bonds. When we eat certain starches, enzymes break down those bonds into glucose, which impacts our blood sugar levels. Some starches, like those found in potatoes, are higher on the glycemic index, which means they break down more easily, leading to faster uptake of glucose and a potential blood sugar spike.

But not all starch is created equal. Certain types can actually be part of a glycemic-friendly diet.

Resistant starch has a unique molecular makeup—either naturally or as the result of heating and cooling—that helps us digest it differently than other starches, so it doesn’t lead to the same blood sugar spikes after meals. In fact, research shows resistant starch can have several health benefits, including improved insulin sensitivity and increased satiety, so you feel less hungry.

"Since we don’t digest resistant starch, a food’s glucose isn’t rapidly released into the bloodstream, and we don’t see a significant blood sugar spike."

The effects of resistant starch vary depending on the dose and type. Here are the mechanisms involved and how to reap the benefits by adding this unique ingredient to your own diet.

What is Resistant Starch?

Resistant starch is a type of starch that cannot be broken down by the digestive system (it’s “resistant” to digestion). Unlike other starches, which get digested in the small intestine and broken down into sugar, resistant starch passes through the small intestine unchanged (more on why below). It then ferments in the colon, where it feeds the friendly gut bacteria there, so it can be classified as a form of fiber.

There are five types of resistant starch:

Note that the same food can have different types of resistant starch, and the amount can change depending on how food is prepared.

In addition to the metabolic benefits of resistant starch, studies suggest it promotes “good” bacteria in the gut microbiome, helping reduce inflammation in the colon and improve digestive health. Researchers have even looked into whether resistant starch can help reduce the risk of colon cancer.

How Resistant Starch Interacts With Glucose and Insulin

Research shows eating resistant starch can improve insulin sensitivity. One study found that overweight or obese men who ate 15 to 30 grams of resistant cornstarch per day for four weeks experienced significant improvement in insulin sensitivity compared to men who ate non-resistant starch. In fact, the study found, “The magnitude of the increase in [insulin sensitivity] … is similar to that observed with weight loss of ~10% of body weight.” Another study included 10 normal weight and 10 overweight female participants and found that moderate amounts of resistant starch (about 6.5 grams) were associated with lower insulin levels in both groups in the two hours following meals.

Other research shows a similar effect in people with metabolic syndrome. A study published in the journal Diabetic Medicine looked at 20 people with insulin resistance who were either given 40 grams of supplemental resistant starch to eat per day for 12 weeks or a placebo. The resistant starch group saw a 19 percent increase in insulin sensitivity on average, while those who received the placebo saw a 14 percent decrease.

In 44 food logs from Levels members that clearly delineated fresh starch versus cold starch, members saw an average of 10 mg/dL lower glucose response with the cooled starch.

So what accounts for the effects of resistant starch on blood glucose? We can think about this relationship in two ways: first, in the short term after a meal and the long run, when resistant starch is a consistent part of our diet.

When we eat other types of starch, enzymes in our small intestine break down the starch into glucose for energy. But since we don’t digest resistant starch, the food’s glucose isn’t rapidly released into the bloodstream. Therefore we don’t see a significant blood sugar spike. What exactly makes resistant starch resist digestion depends on the type.

In the long term, eating resistant starch over time improves how the body responds to insulin. Research shows that when resistant starch ferments in the colon, it produces short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate. Acetate, in particular, is known to inhibit the breakdown of fat tissue, so elevated levels of this short-chain fatty acid lead to a decrease in circulating free fatty acid concentrations. This is important because high circulating free fatty acid concentrations are associated with decreased insulin sensitivity. In other words, lower levels of free fatty acids mean improved insulin sensitivity.

Researchers are also looking at how resistant starch impacts gene expression in fat tissues, which may affect how fat is stored in the body, keeping it out of other areas where it can do harm, such as the muscles, liver, kidneys, pancreas, and the heart.

Ways to Incorporate Resistant Starch into Your Diet

There is no official recommendation for daily intake of resistant starch. In research studies, health benefits have been seen with consumption of 15 to 60 grams per day. Food labels do not list an amount of resistant starch content, so it is not always easy to determine. Still, for context, research shows 100 grams (about 3 and a half ounces) of oatmeal flakes contain around 3.6 grams of resistant starch, while many legumes have between 1 and 5 grams per 100-gram serving.

(Another way to think of resistant starch intake is in the context of fiber intake—recommended to be about 25-38 grams a day—since it is basically a form of fermentable fiber, or fiber that is “eaten” by good bacteria in the colon. Resistant starch appears to produce more healthy butyrate than typical soluble fiber, so it’s a helpful addition to your diet beyond your regular sources of fiber.)

In general, resistant starch appears to be well tolerated at 45 grams per day with few gastrointestinal side effects. Eating more than can lead to uncomfortable symptoms of gas and bloating.

According to a study published in August 2020 in The Journal of Nutrition, adults in the United States consume about 4 grams of resistant starch per day. Research shows Europeans tend to get 3 to 6 grams of resistant starch per day, while people in China get around 15 grams per day. Some countries in Africa consume 20 to 30 grams of resistant starch daily.

Americans could benefit from adding more resistant starch to their diets. Some steps you can take to do this include:

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