Resistant Starch: Health Benefits & Safety

Answer:

What Is Resistant Starch?

Starches function as a major dietary source of carbohydrates for humans. In contrast to rapidly digestible starch, as found in white bread, pasta, and cooked potatoes, which is quickly digested to sugar (glucose) by enzymes in the mouth and small intestine, resistant starch can only be broken down when it reaches the large intestine (the colon). There, resistant starch is fermented by gut bacteria to form short-chain fatty acids (SCFAs).

This is similar to how soluble, fermentable fibers found in foods such as oats, beans, and onions, and in prebiotics made with inulin and guar gum, are fermented. The SCFAs formed by resistant starch are higher in butyrate than SCFAs made from soluble fibers (Sajilata, Compr Rev Food Sci Food Saf 2006). 

Because it is not broken down into glucose, resistant starch contributes somewhat fewer calories than digestible starch: Digestible starch provides about 4 Calories per gram, while resistant starch provides about 2.5 Calories per gram (Higgins, Crit Rev Food Sci Nutr 2014).

There are four types of resistant starch, although more than one can coexist in the same food (Baptista, Front Nutr 2024). Keep in mind that the amount of resistant starch in nearly all foods is generally very low, as discussed below and shown, by food, in the large table further below.

• Type I (RS1): Found in partially milled grains, seeds or legumes (e.g., beans, lentils, chickpeas). The starch is encased within intact plant cells walls or a dense food matrix. However, a 100-gram serving (about ½ cup) of cooked beans or lentils, which generally contains about 27 grams of total starch, typically provides only about 1 to 6 grams of resistant starch. Similarly, a 100-gram (about ½ cup) serving of cooked grains such as barley contain about 19 grams of total starch, of which only about 1 gram is resistant starch (Patterson, J Acad Nutr Diet 2020).
• Type 2 (RS2): Found in raw potatoes, green bananas, some legumes, and high-amylose corn (e.g., HI-MAIZE®260). The starch has a compact, crystalline organization that, if uncooked, makes it inaccessible to digestive enzymes. A raw green banana contains about 2.8 grams of resistant starch per 8 grams of total starch, a raw green plantain contains about 5 grams per 13 grams of total starch, while 100 grams (about 2/3 cup) of raw potato contains about 5 grams of resistant starch and 13 to 21 grams of total starch (Cao, Nutrients, 2022; Patterson, J Acad Nutr Diet 2020).
• Type 3 (RS3): Found in small amounts in some (but not all) cooked then cooled foods, such as potatoes and rice, as well as some bread that is frozen and then toasted. Formed when the digestible starches in these foods undergo structural changes upon cooling or toasting that makes the starch indigestible. However, 100 grams (about ½ cup) of cooked short-grain white rice, which contains about 28 grams of starch, provides 0.3 grams of resistant starch, and this increases to only 0.4 grams if the rice is then cooled. Cooked long-grain white rice has slightly more resistant starch (about 1 gram per half cup) and this hardly changes when cooled (Patterson, J Acad Nutr Diet 2020). Among bread products, white bread contains only about 1 gram of resistant starch per 100 grams (2 to 3 slices containing about 45 grams of total starch), while toasted white bread contains just slightly more: 1.9 grams. Even breads considered to be "better" sources of resistant starch actually contain very little: Mixed grain bread contains 2.6 grams, wheat sourdough bread contains 3.3 grams, and rye bread contains 3 grams per 100 grams of bread. Cooked, regular pasta has only 1.5 grams of resistant starch per 100-gram serving, with no increase with cooling, although the amount in durum wheat pasta was shown to increase from 1.2 grams to 3.4 grams when chilled for 3 to 5 days (Patterson, J Acad Nutr Diet 2020). Resistant starch is also found as a minor constituent in cornflakes, but represents less than 3 grams per 100 grams for the Kellogg's brand — which, even at six large bowls, was not found to affect bowel habits (Tomlin, Br J Nutr 1990).
• Type 4 (RS4): Chemically modified starches (e.g., VERSAFIBE®, NOVELOSE®) that have been cross-linked to prevent digestion.

What Are the Health Benefits of Resistant Starch?

Resistant starch has been promoted for numerous conditions. As discussed below, there is some evidence that 25 to 40 grams daily of type 2 resistant starch (typically high-amylose maize) may help with blood sugar control and insulin levels in people with type 2 diabetes, as well as with fatty liver disease. The evidence is mixed for helping with weight loss, and studies suggest little to no benefit in improving bowel function.

Diabetes and Blood Sugar Control — Possible Benefit

There is some evidence that consuming type 2 resistant starch can improve blood sugar control and insulin levels among people with type 2 diabetes, although it is not clear if it reduces the risk of developing type 2 diabetes. Type 3 resistant starch may reduce blood sugar spikes among people with type 1 diabetes. Other types of resistant starches do not appear to be help, and no resistant starch appears to significantly benefit people with prediabetes.

When the U.S. FDA was asked if it would authorize a health claim regarding the consumption of high-amylose maize starch (a type 2 resistant starch) and reduced risk of type 2 diabetes, it declined to give its approval but indicated that it would not necessarily object to such a claim if were followed by "…, although the FDA has concluded that there is limited scientific evidence for this claim" (FDA 2016). The European Food Standard Authority allows foods to include the health claim "replacing digestible starch with resistant starch induces a lower blood glucose rise after a meal" if at least 14% of digestible starch in the food is replaced with type 2 resistant starch (EFSA, EFSA J 2011).

An analysis of 36 randomized controlled trials including 982 participants with type 2 diabetes or prediabetes showed that consuming foods in which some of the digestible starch was replaced with type 2 resistant starch (6 to 40 grams daily for 1 day to 1 year) modestly lowered fasting and post-meal blood sugar and fasting insulin levels compared to control among those with type 2 diabetes but not prediabetes. Consuming type 1 or type 4 resistant starch did not significantly affect these outcomes. Interestingly, consuming resistant starch did not significantly affect concentrations of hormones that affect satiety (Pugh, Front Nutr 2023).

One study that did not show a benefit was conducted in Malaysia among 82 adults (average age 57) with type 2 diabetes. The study showed that 25 grams of a type 2 resistant starch (sago starch; 44% resistant starch), added to 200 mL of water and consumed twice daily before meals for 12 weeks, did not significantly improve HbA1c, levels of fasting glucose or fasting insulin, insulin resistance, or cholesterol and triglyceride levels compared to placebo (King, Clin Nutr ESPEN 2025).

In a small study of 32 young adults with type 1 diabetes, eating 200 grams (about 1.5 to 2 cups) of cooled-then-reheated wheat pasta reduced the blood sugar spike after eating (from about 227 to 193 mg/dL) and reduced the duration of high blood sugar compared to eating the same pasta that was cooked but not cooled (Fogowicz-Frontczak, Nutrients 2026). The cooked pasta reportedly contained 8.03 grams of resistant starch per 100 grams, while the pasta that was cooked then cooled (to 39 °F for 1 day) and reheated (in hot water for 3 minutes) contained 12.88 grams/100 grams, which is much greater than the amounts reported by others (see table).

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) — Possible Benefit

A study among adults (average age 39) with MASLD (previously called nonalcoholic fatty liver disease or NAFLD) showed that consuming 40 grams per day of the type 2 resistant starch high-amylose maize (from Ingredion, which did not fund the study) while following a standard diet for 4 months decreased liver fat by 11.85% compared to baseline, and this was significant compared to the control group (standard diet + control starch) that showed a reduction of only 2.07%, although participants in both groups were still considered to have mild steatosis at the end of the study. Those in the resistant starch group also showed greater reductions in levels of liver enzymes ALT (-10.96 vs -4.43 U/L), AST (-4.8 vs -1.44 U/L) and GGT (-6.14 vs -3.62 U/L), as well as total cholesterol (-8.1 vs 0 mg/dL), triglycerides (-39.9 vs +8 mg/dL), body weight (-12 vs -2 lbs), and visceral fat area (-26.39 vs -6.02 cm²) compared to control (Ni, Cell Metab 2023).

Improving Bowel Function — No Significant Benefit

Resistant starch is commonly promoted for improving bowel function, although benefits appear to be mixed and modest at best, and may not be clinically meaningful. The European Food Standard Authority has chosen to not approve health claims related to digestive health benefits of resistant starch (EFSA, EFSA J 2011).

A study in Canada among 70 healthy adults showed that consuming 3.5 or 7 grams of a type 2 resistant potato starch daily for 4 weeks did not significantly improve abnormal bowel symptoms such as bloating, constipation, abdominal pain or diarrhea compared to placebo (digestible corn starch) (Bush, BMC Nutr 2024). Similarly, a study in Japan among 46 healthy adults showed that consuming bread containing 3.26 grams of wheat-derived resistant starch daily for 4 weeks did not significantly improve the frequency of bowel movements compared to control, although there was evidence of slight increase in bowel movement frequency compared to placebo among those with low stool frequency at baseline (Kikuchi, Biosci Biotechnol Biochem 2025).

A study among 87 adults with chronic constipation showed that those who consumed 9 grams of type 3 resistant starch (Haruna Plus®) daily for 12 weeks tended to have slightly more bowel movements per week compared to those receiving placebo (4 to 5 vs. 2 to 3), but the difference was not statistically significant and there was no between-group difference in stool consistency (Luk-In, Sci Rep 2024).

Weight Loss — Generally Not Helpful

Although a number of studies suggested that resistant starch may lower fat mass or increase lean body mass in animals (Higgins, Crit Rev Food Sci Nutr 2014), but clinical research in humans mixed. Resistant starch does not appear to significantly reduce body weight or body fat when used short-term or along with usual diet. In fact, one study suggested that resistant starch could slightly increase body fat. However, taking resistant starch in combination with a low-fat diet may slightly reduce body weight and visceral fat by boosting certain gut bacteria.

Taking 30 grams of type 2 or 3 resistant starch daily for 1 week did not significantly reduce appetite or food intake among healthy men in one study (de Roos, Eur J Clin Nutr 1995). Similarly, a study in California among healthy adults (age range 40 to 65) showed that consuming rolls made with type 2 wheat-derived resistant starch for one week did not significantly affect feelings of hunger or fullness compared to placebo (Hughes, Appetite 2022). Also, consuming 40 grams of resistant starch daily for 12 weeks did not significantly affect body weight or visceral fat deposits compared to placebo among 20 insulin resistant adults (Johnston, Diabet Med 2010), and incorporating 30 grams of type 2 resistant starch into every day foods daily for 4 weeks did not significantly reduce body weight, BMI, or fat mass compared to placebo among healthy adults (Robertson, Am J Clin Nutr 2005). In these two latter studies, the participants followed their regular diets.

A small study among 30 women with risk factors for metabolic syndrome who followed their regular diets showed that increasing daily intake of resistant starch from 2.6 to 7.9 grams per day from a special breakfast cereal or energy bar once daily for 5 days a week over 8 weeks, resulted in statistically significant increases in body weight (+0.8 kg), body fat percentage (+1.1%), visceral fat area (+8.1 cm²), and triglycerides (+41.2 mg/dL) compared to baseline, while those in the low resistant starch diet group showed no significant changes in these outcomes. Neither group showed significant changes in blood sugar, waist circumference or muscle mass, although the those in the high resistant starch group had a modest reduction in blood pressure (133.5 to 129.3 mmHg), which was not seen in the low resistant starch group (Kim, Nutrients 2025).

A small study in China among 37 otherwise healthy overweight adults (average age 33) following a low-fat diet (25% to 30% fat) showed that consuming 20 grams twice a day of type 2 resistant starch from high-amylose maize mixed in water 10 to 15 minutes before a meal for 8 weeks reduced body weight by 6.2 lbs and visceral fat area by 22.19 cm² compared to baseline, and these changes were significant compared to the control group (control starch) that showed no significant improvements in these outcomes. Neither group showed significant improvements in total cholesterol, triglycerides, low-density lipoprotein (LDL or "bad") cholesterol, or blood pressure. Interestingly, the study found that an increased abundance of B. adolescentis after resistant starch treatment was linked with greater decrease in BMI and visceral fat, suggesting that resistant starch may help with weight loss by boosting this gut bacteria (Li, Nat Metab 2024). Somewhat similarly, another small study in China among 19 adults with normal body weights showed that taking 40 grams per day of type 2 resistant starch from high-amylose maize while following a low-fat diet for 4 weeks significantly reduce visceral fat area compared to control group (control starch + diet), although this study found no between-group differences in weight, body mass index, fat mass or waist circumference (Zhang, Sci Rep 2019).

Is Resistant Starch Safe

When consumed as part of the diet, resistant starch is generally considered safe. The most common side effect reported in clinical studies are gastrointestinal disorders including constipation, flatulence/bloating, and loose stools (King, Clin Nutr ESPEN 2025).

As discussed earlier, one study found that adding resistant starch to the diet resulted in a slight increase in body fat and triglyceride levels (Kim, Nutrients 2025).

How Much Resistant Starch Is In Most Foods?

Many commonly consumed foods contain resistant starch, but the amount is generally very low — even among foods promoted as being a good source of resistant starch. Listed in the table below are the grams of resistant starch per 100 grams of various foods (Australian Food Composition Database 2026; Bojarczuk, Metabolites 2024; Hou, Int J Mol Sci 2020; Patterson, J Acad Nutr Diet 2020; Chen, Asia Pac J Clin Nutr 2010; Murphy, J Acad Nutr Diet 2008). For reference, 100 grams is approximately the weight of one banana, 2 to 3 "sandwich" slices of bread, 2.5 cups of breakfast cereal, ½ cup of cooked legumes, ¾ cup of cooked pasta, 2/3 cup of cooked potatoes, or ½ cup of cooked rice.

Be aware that the values shown below are based on the preparation state shown. Amounts of natural resistant starch will be affected by further preparation. For example, chilling may increase resistant starch but reheating after chilling will reduce natural resistant starch. Heating potatoes in water, for example, increases the solubility of the resistant starch granule to improve digestibility and reduce resistance, thus lowering resistant starch content. Similarly, cooking oats almost entirely reduces its resistant starch content (although its fiber remains) (Patterson, J Acad Nutr Diet 2020).

Some brands of keto or low-carb breads such as Hero, Royo, and Sola list resistant wheat starch as one of the main ingredients. These breads typically provide a significant amount of fiber (7 to 12 grams per slice) and are low calorie (30 to 45 calories/slice), but the amount of resistant starch in these products is typically not listed. ConsumerLab reached out to each of these brands on March 30, 2026 to find out how much resistant starch is in their bread products, and we will post responses when received.