Resistant starch is a powerful prebiotic fiber that supports gut health, lowers blood sugar, and promotes satiety. Learn how common foods like potatoes, rice, beans, and pasta can become rich in resistant starch just by chilling them after cooking. Discover the science behind this nutrient and how to get the 30 grams per day shown to improve metabolic health.
Resistant starch. If this term is new to you, it won’t be for long. It’s a hidden gem found inside our most loved starchy foods, and the best part is you can get more of it by just changing the cooking and storage method. You see, resistant starch is a health changer because not only does it reduce the amount of available (digestible) starch in starchy foods, it also provides fuel for our good gut microbes.
Starchy foods like potatoes, beans, legumes, peas, pasta, rice, cereals, and tortillas are common diet staples among Americans. They are relatively low in cost, provide energy in the form of carbohydrates (starch is a carbohydrate), and many contain fiber. Starch, made solely of glucose molecules, packs together to form granules in food. The starch in these granules can be fully digested; however, some components of starch in the granules “resist” digestion. The enzymes in our small intestine simply cannot access this component of starch, either because the starch is packed tightly or there is a shell covering these glucose molecules. Bottom line, these starch components are not broken down in the small intestine, so they enter the large intestine unharmed in its original form. This is called resistant starch.
How Resistant Starch Acts as a Prebiotic Fiber
Certain good bacterial species in our large intestine “eat” resistant starch, a process known as fermentation. The products of fermentation include the following short chain fatty acids: acetate, butyrate, and propionate. Cells that line our large intestine have receptors in which these short chain fatty acids can bind to, especially butyrate. When butyrate binds to these cell receptors, they stimulate the release of incretins, like glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). Incretins have many roles in the body including promoting insulin release from the beta cells in the pancreas, which helps lower blood sugar after meals. These incretins also play a role in our appetite by telling our brain when to stop eating (aka promoting satiety). They also have other roles impacting our cardiometabolic health.
If you think about the roles resistant starch plays in our gastrointestinal (GI) tract, it has two main ones: reducing blood sugar because it resists digestion in the small intestine so less glucose is available to be absorbed into the blood, and by providing fuel for the good gut microbes, it is a prebiotic fiber. Not all fibers are prebiotics. For example, if the fiber is not fermented by the good gut bacteria, it is not a prebiotic. Good bacteria is the key! And the products from fermentation must provide a benefit to the host, aka you and me.
How Much Resistant Starch is Found in Our Foods?
We published a paper in the Journal of the Academy of Nutrition and Dietetics in 2020 that quantified the amount of resistant starch in commonly consumed foods in the US (Table 1). Many factors impact resistant starch, such as growing conditions and environment, plant species, storage conditions and duration, and food ripeness. In the Table notice that beans contain different amounts based on variety. Also, greener or unripe bananas contain more resistant starch than ripe ones because, over time the starch becomes more digestible as part of the ripening process. This is true for plantains, as well.
The foods with the highest amounts of resistant starch include lima beans, baked potatoes, and kidney beans. Boiled potatoes contain resistant starch, but much less than baked potatoes. Adding both heat and water during cooking causes the starch granules in the raw potato to open up and a gel-like environment is formed. Opening the granule allows for our enzymes to access the starch and become more digestible. However, with the baked potato, only one element (heat) is added. Thus, the starch granules don’t open up as much which allows for some of the resistant starch inside the granule to remain.
Table 1. Amount of resistant starch per serving in starchy foods
Increasing the Amount of Resistant Starch in Foods is SO Easy!
The one method that allows for the most resistant starch is by chilling the starchy food after cooking. While cooking opens and gelatinizes the starch granule, chilling causes the starch gel to compact. This process, called retrogradation, actually re-creates resistant starch at higher levels than when cooked. Here are some examples:
· Baked russet potato = 8.8 g of resistant starch for medium-to-large potato
· Potato salad = 14.5 g resistant starch for about ¾ cup
By chilling the potato after it has been cooked, the resistant starch content increases ~85% compared to the baked version. What an easy, simple way to get more of this prebiotic fiber in your diet.
The same principle applies to rice, pasta, beans, and tortillas. And if you are concerned about reheating after chilling, rest assured, some of the resistant starch formed during retrogradation remains intact. Finding ways to eat starchy foods cold, like in a salad or soup, automatically amps up dietary resistant starch intake.
How Much Resistant Starch Do We Eat Every Day?
Using data from over 5,000 US adults, we found the average intake to be about 4 grams of resistant starch per day (if consuming a 2,000 kcal diet). The amount consumed did not differ across sex or age; however, non-Hispanic whites had the lowest intake compared to other ethnic groups. Unfortunately, the food contributing the most dietary resistant starch was French fries and other fried potatoes. Yes, even French fries contain about 5 grams of resistant starch per serving. However, as a dietitian, I recommend choosing baked, or better yet, baked then chilled potatoes instead of fried.
How Much Resistant Starch is Recommended?
Clinical studies show a minimum of 15 g of resistant starch per day is needed to show improvements in blood sugar, insulin, and gut health. Based on my research, I recommend at least 30 g per day. We conducted a pilot study that included adults with prediabetes. They consumed a high resistant starch menu (breakfast, lunch, snack, and dinner) for one week and had blood tested at baseline and final. All food was prepared in the research kitchen for all subjects. We found reductions in both blood sugar and insulin in just one week (Figure 1)! The subjects even lost about 2% of their body weight. Many said they just couldn’t eat all the food because it was very filling. Resistant starch is known to increase satiety, so this finding was not surprising. Imagine if the feeding study occurred over several weeks what improvements in metabolic health we would have found. Of note, it was challenging to develop the menu to have ~30 g of resistant starch per day. It can be done, but it requires plenty of beans and legumes, chilled potatoes and pasta, and overnight oats.
Figure 1. Changes in blood glucose and insulin after consuming a high resistant starch diet for 1 week among adults with prediabetes.
In conclusion, resistant starch is a prebiotic fiber that acts in both the small intestine to decrease the amount of digestible starch, and in the large intestine to impact the gut microbiome. The recommended 30 grams of resistant starch per day can be achieved by including high resistant starch foods and by chilling cooked foods and eating them cool. However, many individuals are not able to eat meals high in resistant starch, so a supplement may be recommended. Resistant starch is slowly digested by the gut microbes so it does not rapidly produce gas that can lead to GI bloating and pain. This necessary nutrient can improve metabolic and gut health, both are key factors in preventing chronic diseases.