Experts explain the resistant starch trend circulating on social media.
By Alice Callahan, New York Times Published Nov. 8, 2023, Updated Nov. 9, 2023
It sounds like just another internet health hack: Cook some pasta or white rice and let it cool overnight in the refrigerator. By the next day, some of the natural starches in the food will have transformed into healthier versions, called resistant starches, which have been linked to a range of health benefits including lower blood sugar, better gut health and a reduced risk of certain types of cancer.
The idea that you could change the health properties of a food by merely cooking and cooling it may sound too good to be true. But according to experts like Balazs Bajka, a gut physiologist at King’s College London, there’s something to it. Cooling starchy foods can cause some changes to their structure that may benefit your health, Dr. Bajka said. Here’s what we know.
What is resistant starch?
Resistant starch is a type of fiber that is naturally present in many types of plant foods, such as whole grains, beans, nuts, seeds, green bananas and plantains. But it can also be increased in other foods that mainly contain regular starch, like rice, pasta and potatoes, after they are cooked and then cooled. Cooking and cooling causes the food’s starch molecules to become tightly packed together, making them more difficult to digest, Dr. Bajka said. When this happens, some of the starch becomes “resistant,” meaning its sugar molecules aren’t as easily broken apart and absorbed into your bloodstream as they normally would be. Even if you reheat the food as leftovers the next day, most of the resistant starch formed during cooling will remain, he added.
What are the health benefits of resistant starch?
Because resistant starches aren’t easily digested, they don’t spike your blood sugar as much as regular starch does, said Kimberley Rose-Francis, a dietitian in Florida who specializes in working with patients with diabetes. Instead, the resistant starch continues on in your intestines, where it can feed the good microbes in your gut, Dr. Bajka said. This helps them flourish and make beneficial molecules that have been linked with lower cholesterol and inflammation and better gut health in general.
There’s also some evidence that resistant starches may play a role in reducing the risk of certain types of cancer, said Annette M. Goldberg, a dietitian at the Dana-Farber Cancer Institute in Boston, though more research is needed. In one recent trial of more than 900 people with Lynch Syndrome, a genetic condition that increases the risk of developing various types of cancer, researchers split the participants into two groups: one that took 30 grams of a resistant starch supplement each day for up to four years, and another that took a placebo.
Up to 20 years later, the researchers found that while there was no change in the participants’ risk of colorectal cancer, those who took the resistant starch supplements were half as likely as those who took the placebo to develop other types of cancers, especially those of the upper gastrointestinal tract, such as in the stomach or pancreas. (The supplements used in the trial were provided by a company that makes starch ingredients, but the company was not involved with the study’s design or analysis.)
When you cook and cool a starchy food, you’re also effectively increasing its fiber content, said Mindy Patterson, an associate professor of nutrition and food sciences at Texas Woman’s University.
Fiber has been linked to a host of health benefits including a reduced risk of heart disease, Type 2 diabetes and some types of cancer. And when consumed as resistant starch, it seems less likely than other forms of fiber to cause unpleasant effects like gas or bloating, Dr. Patterson said.
The bottom line
Most people will benefit from consuming more fiber, whether it’s in the form of resistant starch or not, Dr. Patterson said. Good sources of fiber include whole grains, fruits, vegetables and legumes. And aside from eating foods that naturally contain resistant starch, like beans, barley, green bananas and oats, you can increase the levels of resistant starch in foods like pasta, potatoes and rice by cooking and cooling them, Dr. Patterson said. This technique may be especially useful for those with Type 2 diabetes or pre-diabetes, she said.
Ms. Rose-Francis encourages many of her clients with diabetes to experiment with cooking and cooling methods with rice, pasta or potatoes to see if that makes a difference in their blood sugar levels.
For them, this can be a powerful technique, she said — since many people with diabetes avoid eating starchy foods over fears that they might spike their blood sugar too high. This may explain why one of her TikTok videos on the topic has been viewed 1.3 million times. “It gives people hope,” she said.
Reader Comments
Mindy Patterson, PhD, RDN Houston, TX Nov. 8 – @RP Actually, I was one of the experts that was quoted in the article. Based on my publication in the Journal of the Academy of Nutrition and Dietetics 2020, here is what we found. – Cooked starches have the least amount of RS – Cooked then chilled starches have more RS than cooked – Cooked then chilled starches for up to 5 days have the most RS (RS increased with each chill day but plateaus around day 5). – Reheating cooked then chilled starches have more then cooked but less than cooked then chilled. Hope this helps!
Alice Callahan Reporter Nov. 9 – @Mindy Patterson, PhD, RDN — Dr. Patterson, thanks for sharing this info with our readers! So very helpful, and we’ve updated the piece now so that this information is in the article. Its an obvious and very practical thing to wonder about!
Dwd DC Nov. 8 – How, exactly, does cooling increase the fiber & in an ultra-processed food whose fiber has been removed? Inquiring minds want to know. Further–even if this were true–does re-heating the (highly-processed) white rice or pasta negate the ostensible benefits? Do you have to eat the pasta or white rice cold? This seems like another half-baked nutrition & story.
Alice Callahan Reporter Nov. 9 – @Dwd – It’s actually really interesting how much debate there has been over the definition of fiber! And it wasn’t until 2009, after several decades of debate, that the World Health Organization published a formal definition of fiber: & all carbohydrates that are neither digested nor absorbed in the small intestine and have a degree of polymerization (DP) of ten or more monomeric units. Resistant starch fits this definition. It’s also naturally present in many whole foods, sometimes because it’s trapped in a complex food matrix, and sometimes just because of the way the sugar molecules in the starch are linked together. I understand your skepticism, but in this case, cooking and cooling does have this effect of making starch less available for digestion. It technically makes the starch a type of fiber, with similar effects on your gut health as other fibers.
Michelle New England Nov. 8 – What this article doesn’t make clear is whether you have to eat the cooked-then-cooled starch cold. Does re-heating it retain any if the possible benefits? Or do those of us who like complex carbohydrates need to get used to eating them cold?
Alice Callahan Reporter Nov. 9 – @Michelle — This is such a great question and highly relevant, since most of us prefer hot rice and pasta! We updated the piece this morning to address this question. The researchers I interviewed for this piece told me that reheating can reduce resistant starch a bit, but you’re still left with more than if you’d eaten the freshly cooked rice or pasta. That said, reporting this piece reminded me of some delicious ways to enjoy cooled starches, like potato salad (which can be prepared in so many ways!) and cooled grains and beans added as toppings for green salads. Fried rice is also an excellent source of resistant starch, when made with leftover rice. Something about cooling in the fridge for a day or two and then frying seems to & more of the resistant starch, according to Dr. Patterson.
Mary Chicago Nov. 8 – Info about reheating, from Johns Hopkins Patient Guide to Diabetes: Cooked rice that has been cooled is higher in resistant starch than rice that was cooked and not cooled. ….Try cooking rice, potatoes, beans, and pasta a day in advance and cool in the refrigerator overnight. It’s ok to reheat the starch before eating. Reheating doesn’t decrease the amount of resistant starch.
GGS NYC Nov. 8 – @Kent Leftover spaghetti is wonderful. Just fry it up, preferably in butter but you can use olive oil, until crisp. Then add a beaten egg, maybe grate over some Parmesan. It’s delicious. While you eat it, you can read one New York Times article about how you shouldn’t eat eggs, cheese, or butter, and another article about the health benefits of all three.
RP North Carolina Nov. 8 – John’s Hopkins says “reheating doesn’t decrease the amount of resistant starch”.
Debbie Hudson Valley Nov. 8 – @Roger’s question seems like such an obvious one to ask. Why didn’t the article address it? I am too often surprised by the questions NYT health reporters and their editors don’t address. If the answer is unknown or too complex for this article, just tell us.
Ann O. Dyne Unglaciated Indiana Nov. 8 – Does re-heating the starch foods undo the stated benefits? Does more time in & cooling & cause increasing percentage of resistant starch?
Jen_NH NH Nov. 9 – For everyone asking about reheating (and yes, the article should have included this detail), for the most part reheating does not change the amount of resistant starch. An exception appears to be potatoes, and that depends on what type of potato is being cooked, cooled, and reheated. I don’t know if links are permitted in NYT comments, but the Johns Hopkins Patient Guide to diabetes has a page detailing this titled What is Resistant Starch? And contains this detail: Reheating doesn’t decrease the amount of resistant starch. And then this added as an addendum: “It may be true that potatoes, for example, may lose some resistant starch in the reheating process. However, the type of potato is also a consideration. The resistant starch in red and yellow variety potatoes does increase after being cooked, chilled, and reheated. Russet potatoes may slightly decrease resistant starch content after reheating.
