Cooling Carbs as a Weight Loss Strategy
Can cold fries help you lose weight?
For lovers of rice, pasta and potatoes, there’s a miraculous new diet tip people are sharing. You start by cooking up rice, pasta or potatoes. Then put them in the refrigerator overnight, so they cool down. Take them out the next day, and those carb-rich foods are now resistant starches. When you eat them, your blood sugar won’t spike, you’ll feel full quicker, and your body won’t absorb as many calories.
According to the experts, the simple carbs you find in pasta, white rice and potatoes go through a process of retrogradation when they’re chilled. Retrogradation turns the carbs into “resistant starches.” The starches your body typically digests have turned into something your body can “resist” digesting.
How Resistant Starches Work
It’s a type of carbohydrate that digests so slowly; it goes through the small intestine without being digested. It “resists” digestion.
When you eat resistant starch, it’s bulky and takes up space in your digestive system. This makes you feel full. Because your small intestine doesn’t absorb or digest it, your body doesn’t turn the excess you eat into fat. As it enters the large intestine, your body ferments it. One byproduct of resistant starch fermentation is the creation of a fatty acid called butyrate, which blocks the body’s ability to burn carbohydrates.
Carbohydrates are the body’s preferred source of fuel. So when butyrate blocks your ability to burn carbs, your body turns to fat instead. A study at the University of Colorado Health Sciences Center found that replacing just 5.4% of daily carb intake with resistant starch increases fat burning by an astonishing 23%.
After hearing this, many people dream of cooking up French fries, pasta and white rice, then cooling them in the refrigerator and heating them the next day for guilt-free indulgences.
There's a problem. There are four types of resistant starch. The one created by “carb cooling” your potatoes, rice or pasta is RS3. But many studies showing resistant starch is good for you only look at RS1 and RS2, which are simply healthy, high-fiber foods like beans, slightly green bananas and whole grains.
Here’s what researchers found when they looked specifically at RS3 or resistant starches created by cooling carbs.
An early study in 1992 measured several resistant starches, including “cooking and cooling potatoes.” After cooling overnight, the researchers found that potatoes “produced a 2.8-fold increase in the amounts of resistant starch.” That sounds great! But another part of the study posed a problem.
Researchers found that “the more times a starch-containing food was chewed, the less starch escaped digestion...” So yes, you can boil potatoes and cool them overnight to make resistant starch, but if you chew and eat them, you lower how much resistant starch you end up with. Chewing doesn’t eliminate the benefit, but it will not be as large as the test tube numbers indicate.
A 2021 study looked specifically at foods with RS3 and fed them to eight healthy males aged 18-35. At the end of the two-week study, researchers concluded that “consuming the RS3 meal was associated with greater satiety and lower desire to eat in young healthy males, which may lead to weight management in the long term.” But that study did not find a benefit in fasting blood glucose, serum insulin or plasma ghrelin.
Another 2021 study came to a different conclusion. After giving freshly cooked rice and rice cooled overnight, they concluded no evidence cooling affected the glycemic index or carbohydrate digestibility.
That was followed by a 2022 study that looked specifically at cooling rice after cooking. They tested 32 patients with type 1 diabetes. One meal had long-grain white rice served immediately after preparation. The other was cooled for 24 hours and reheated before being served. The test meal with rice that had been previously cooled had a “significantly lower value of maximum glycemia.” In other words, it didn’t spike the patient’s blood sugar nearly as much. These were the same results as a 2015 study that looked at the same thing.
Resistant Starches - This is a list of the four different types of resistant starches.
Resistant Starch 1 [RS1]
RS1 includes things like Barley, whole grains, brown rice, beans and legumes cooked intact are one type. The fibrous "shell" makes it difficult for the small intestines to break down. If you can avoid it, don't mix beans with products like Bean-o. While Bean-o increases the digestibility of beans, it decreases the amount of resistant starch.
Resistant Starch 2 [RS2]
RS2 includes slightly green bananas, plantains, high-amylose corn and raw potatoes. They have a chemical structure that digestive enzymes can't break down.
Resistant Starch 3 [RS3]
RS3 is the one being hyped. It includes a few starchy foods that are cooled before eating. When some starchy foods are cooked, the starch absorbs water and swells. As it cools, a portion of the starch crystallizes into resistant starch. Potatoes (like those in a potato salad) and rice (rice pudding) are two examples.
Resistant Starch 4 [RS4]
RS4 is made synthetically. It is unclear if artificially made resistant starches have the same beneficial effects the other three types have, so I would avoid them until more research has been done.
What that means for you is complicated. Eat plenty of RS1 and RS2 resistant starches because they’re foods that provide lots of different healthy benefits.
If you’re determined to eat higher carbohydrate RS3 foods like white rice, potatoes or pasta, refrigerate them overnight before eating. Right now, there’s some evidence they will help make you feel fuller for longer periods and lead to a lower increase in blood glucose.
As with any diet recommendation, eat these in moderation. Unfortunately, for definitive results, we will have to wait for more extensive studies in the future.
Since there is no recommended daily amount of resistant starch to eat, the best we can offer is a suggestion. According to a study published in the May 2008 Journal of the American Dietetic Association, American adults eat about 5.5 grams of resistant starch daily. Research suggests we should at least double that to 11 or 12 grams daily. Eating just 1 cup of beans, 2 bananas, or 1.5 cups of potatoes would be sufficient. The best way is to replace simple carbohydrates with ones that have resistant starch in them.
Measurement of resistant starch: factors affecting the amount of starch escaping digestion in vitro
J G Muir, K O'Dea
The American Journal of Clinical Nutrition, Volume 56, Issue 1, July 1992, Pages 123–127, https://doi.org/10.1093/ajcn/56.1.123
Effect of cooling of cooked white rice on resistant starch content and glycemic response
Steffi Sonia, Fiastuti Witjaksono, Rahmawati Ridwan
Asia Pacific Journal of Clinical Nutrition, 2015;24(4):620-5. doi: 10.6133/apjcn.2015.24.4.13.
Impact of resistant starch type-3 on glucose metabolism and appetite in healthy males
M. H. Alhussain, A. Almousa and A. Alhowikan
Proceedings of the Nutrition Society, Volume 80 , Issue OCE2: Spring Conference, 29–30 March 2021, Gut microbiome and health , 2021 , E66 DOI: https://doi.org/10.1017/S0029665121000781
Neither low salivary amylase activity, cooling cooked white rice, nor single nucleotide polymorphisms in starch-digesting enzymes reduce glycemic index or starch digestibility: a randomized, crossover trial in healthy adults
Thomas M S Wolever, Ahmed El-Sohemy, Adish Ezatagha, Andreea Zurbau, Alexandra L Jenkins
The American Journal of Clinical Nutrition, Published: 22 July 2021 Volume 114, Issue 5, November 2021, Pages 1633–1645, https://doi.org/10.1093/ajcn/nqab228
Influence of resistant starch resulting from the cooling of rice on postprandial glycemia in type 1 diabetes
Sylwia Strozyk, Anita Rogowicz-Frontczak, Stanislaw Pilacinski, Joanna LeThanh-Blicharz, Anna Koperska & Dorota Zozulinska-Ziolkiewicz
Nutrition & Diabetes, Published: 16 April 2022
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