What is Resistant Starch?

What is Resistant Starch?

Written by: Brandy Ireland, Dietetic Intern

Let’s start off with what starches are in general. Rapidly digestible starches are found in high amounts in starchy foods such as potatoes and bread that are cooked by moist heat. This type of starch is converted into glucose within 20 minutes from the start of enzyme digestion. Slowly digestible starches take about 100 minutes to convert fully into glucose by the digestive enzymes (1). Resistant starch, by contrast, is undigestible by these enzymes and is considered a type of dietary fiber as it passes through the body without wholly contributing to calories. 

What foods have resistant starch?

There are four types of resistant starches classified by their pattern of structure. The first category is resistant starch 1 or RS1, they’re physically enclosed starches such as grains, seeds, and are found in cereals. RS2 has a structural pattern that makes them inaccessible to enzyme digestion. This type is most widely studied by scientists and includes slightly green bananas and potatoes. RS3 types are formed during the cooking then cooling process. The cooling of the starch returns the highly digestible starch back into undigestible starch. For example, cooking macaroni and then allowing it to cool to make a macaroni salad gives it more resistant starch than if you were to eat the macaroni while it is still hot. The fourth type of resistant starch, RS4, is modified starch that you would find in processed foods. You would see it listed in the ingredients as “modified starch”. Foods that have the highest amount of resistant starch are brown rice, whole grain cereals, potatoes, yams, green banana flour, beans, and a product called hi-maize corn flour. The hi-maize can be found on grocery shelves and can be used in baking by replacing up to a quarter of traditional flour called for in recipes. 

How does resistant starch impact blood sugars?

Resistant starch doesn’t enter the bloodstream because the body cannot digest it. It escapes digestion and reaches the large intestine where it may be digested by the gut microflora providing other benefits(1). Insulin resistance is a condition related to diabetes and obesity where the body no longer responds to the hormone. Since the body does not respond to insulin the cells do not know that they need to bring glucose into the cell, therefore it stays in the blood creating a spike in blood sugars after a meal. A meta-analysis from 2019 indicated that supplementing with resistant starch may reduce insulin resistance associated with type 2 diabetes and obesity (2). 

What are the health benefits of resistant starch?

Resistant starch has a lot of promise to improve health. Resistant starch contains only about half the amount of calories as digestible starches.  In a 2004 study, researchers found that there was increased fat oxidation, meaning reduced fat storage in the body when participants consumed about 35 grams of hi-maize in a 2,600 calorie diet (3). The researchers examined the effect of 50 grams of hi-maize but did not see the same beneficial effects suggesting that adding resistant starch to the diet could prevent fat accumulation in the body over the long run and that more is not better. There have been some other indications that resistant starch increases absorption of calcium and iron, and improves cardiovascular health by lowering total cholesterol. Bear in mind these studies were conducted with animals and the results do not always transfer over to the same benefits in people. Resistant starch is also being widely used in high-fiber foods which actually makes them tastier than traditional added-fiber foods.

Bottom line

Resistant starch can be beneficial to your health. More studies are needed to fully understand all the positive impacts it may make in human health. Overall, swapping a few frequently consumed starches with resistant starch options may lead to better blood sugar readings after meals and increase dietary fiber, which many Americans are falling short on. As with all dietary fibers, it is recommended to increase gradually and consume plenty of water to avoid uncomfortable bloating and cramping. 


  1. Sajilata, M. G., Singhal, R. S., & Kulkarni, P. R. (2006). Resistant starch–a review. Comprehensive reviews in food science and food safety, 5(1), 1-17.
  2. Gao, C., Rao, M., Huang, W., Wan, Q., Yan, P., Long, Y., Guo, M., Xu, Y., & Xu, Y. (2019). Resistant starch ameliorated insulin resistance in patients of type 2 diabetes with obesity: a systematic review and meta-analysis. Lipids in health and disease, 18(1), 205. Higgins, J. A., Higbee, D. R., Donahoo, W. T., Brown, I. L., Bell, M. L., & Bessesen, D. H. (2004). Resistant starch consumption promotes lipid oxidation. Nutrition & metabolism, 1(1), 8
  3.  Higgins, J. A., Higbee, D. R., Donahoo, W. T., Brown, I. L., Bell, M. L., & Bessesen, D. H. (2004). Resistant starch consumption promotes lipid oxidation. Nutrition & metabolism, 1(1), 8.

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