Resistant starch: your questions about cooked-and-cooled carbs

Leftover rice and cold potato salad rarely show up on lists of gut-friendly foods. But cooking and then cooling starchy foods increases the share of starch your small intestine can't digest, and researchers have been studying what that means for the gut.

Here are answers to the most common questions about resistant starch, including whether it's worth trying if you bloat easily.

What is resistant starch?

Resistant starch is starch that isn't digested in the small intestine. It reaches the colon intact, where some types can be fermented by gut bacteria, and it's counted as a type of fiber. Researchers describe five types. Types 1, 2, 3 and 5 occur naturally in foods, while types 2, 3 and 4 can also be added to foods as ingredients (Patterson et al., 2020).

A review of foods commonly eaten in the US found resistant starch in breads, breakfast cereals, snack foods, bananas and plantains, grains, pasta, rice, legumes and potatoes.

Does cooking and cooling really make a difference?

Yes. The same review found that foods that are cooked and then chilled have more resistant starch than foods that are only cooked. Foods with more amylose, one of the two main components of starch, also tend to have more (Patterson et al., 2020).

A study on white rice shows the scale. Freshly cooked rice contained 0.64 grams of resistant starch per 100 grams. Rice cooled for 10 hours at room temperature had 1.30 grams, and rice chilled for 24 hours at 4°C (about 39°F) and then reheated had 1.65 grams. In 15 healthy adults, the chilled and reheated rice produced a lower blood sugar response than freshly cooked rice (Sonia et al., 2015).

Two practical notes. Reheating didn't erase the increase in that study. And for food safety, refrigerate cooked rice promptly rather than leaving it out on the counter.

What does resistant starch do in the gut?

When bacteria ferment resistant starch, they produce short-chain fatty acids, including butyrate. In one study, 174 healthy young adults added resistant starch from potatoes, resistant starch from maize, inulin, or a digestible corn starch control to their diets for two weeks. Potato resistant starch led to the largest increase in total short-chain fatty acids, including butyrate. Maize resistant starch and inulin didn't significantly raise butyrate in stool (Baxter et al., 2019).

Responses also depended on which bacteria people already had. So resistant starch doesn't do the same thing in every gut, and results from a powdered supplement don't automatically translate to a bowl of leftover potatoes.

Will it help my blood sugar?

The evidence in women is less clear than headlines suggest. In one trial, 33 adults with a large waist size, 22 of them women, average age 49.5, took 0, 15 or 30 grams a day of resistant starch from high-amylose maize for four weeks each. Insulin sensitivity improved in the men at both doses. In the women, there was no difference between the treatments (Maki et al., 2012).

That's one small trial using a concentrated supplement, not food. It's still a useful reminder that results can differ between men and women, and that a finding in one group doesn't automatically apply to women in midlife.

Will resistant starch make me bloated?

It might, especially in larger amounts. In a small pilot study, six people with IBS and five healthy volunteers took rising doses of a resistant starch supplement: 10, 15 and then 20 grams a day, for three days each. Overall symptoms didn't change significantly from baseline.

But in the people with IBS, every dose of resistant starch increased bloating. The authors described the symptoms as mild and the supplement as generally tolerated (So et al., 2022).

With only 11 participants, that study can't settle the question. It does suggest that if your gut is sensitive, resistant starch is best added gradually.

How can I try it without overdoing it?

• Start with food, not powder. A normal portion of cooked and cooled potatoes, rice or pasta is an easy way to add some resistant starch.
• Cook once, eat twice. Make extra potatoes or rice at dinner, refrigerate the leftovers, and use them the next day in a salad or reheated.
• Keep portions modest at first, and change only one thing at a time.
• If beans already bother you, start elsewhere. Legumes contain resistant starch too, but potatoes or rice are a simpler first test.
• Be cautious with concentrated supplements. The doses in the blood sugar and bloating studies above ranged from 10 to 30 grams a day, which is a lot of fermentable material to add at once.
• Track your bloating on a 0 to 10 scale for two weeks.

Who should check with a doctor first?

If you have diabetes and take glucose-lowering medication, talk with your care team before making big changes to your carbohydrate intake. And see a doctor for red flags, like blood in your stool, unexplained weight loss, anemia or new bloating most days.

Sources

1. Patterson MA, Maiya M, Stewart ML. Resistant starch content in foods commonly consumed in the United States: a narrative review. J Acad Nutr Diet. 2020;120(2):230-244. PMID 32040399
2. Sonia S, Witjaksono F, Ridwan R. Effect of cooling of cooked white rice on resistant starch content and glycemic response. Asia Pac J Clin Nutr. 2015;24(4):620-5. PMID 26693746
3. Baxter NT, Schmidt AW, Venkataraman A, Kim KS, Waldron C, Schmidt TM. Dynamics of human gut microbiota and short-chain fatty acids in response to dietary interventions with three fermentable fibers. mBio. 2019;10(1):e02566-18. PMID 30696735
4. Maki KC, Pelkman CL, Finocchiaro ET, et al. Resistant starch from high-amylose maize increases insulin sensitivity in overweight and obese men. J Nutr. 2012;142(4):717-23. PMID 22357745
5. So D, Yao CK, Gibson PR, Muir JG. Evaluating tolerability of resistant starch 2, alone and in combination with minimally fermented fibre for patients with irritable bowel syndrome: a pilot randomised controlled cross-over trial. J Nutr Sci. 2022;11:e15. PMID 35291272

This article is for general information and isn't medical advice. If you have diabetes, a digestive condition or take medication, talk to your healthcare provider before making big changes to your diet.