Is it true that when you cool pasta, rice or potatoes, it produces resistant starch, and therefore the body absorbs significantly fewer carbohydrates?
Claude Landry
Our reader Claude Landry draws this statement from the documentary The Truth About… Carbsbroadcast in 2018 by the BBC, and rebroadcast since 2021 on Ici Explora (The Truth About Carbs).
In the one-hour episode, taken from the series The Truth About, British doctor Alexander van Tulleken explores healthier ways to consume carbohydrates. It further supports this: cooling, freezing and reheating already cooked starchy foods (bread, rice, potatoes, pasta) “transforms refined starch into resistant starch”. “Surprisingly,” he says, “freezing and then toasting means your body gets far fewer calories. Resistant starch feeds your gut bacteria instead of feeding you. »
“Should we believe these claims? our reader asks. If so, does this have a significant impact on blood sugar measurement, particularly for a diabetic? »
The short answer: no. “There is not enough evidence to make this type of claim,” responds May Faraj, professor at the University of Montreal (UdeM) and director of the Nutrition, Lipoproteins and Cardiometabolic Diseases Research Unit of the Montreal Clinical Research Institute. The idea of cooling and reheating food, moreover, does not appear in the guidelines of Diabetes Canada or the American Diabetic Association nor in those of clinical practice for obesity, she points out.
Starch is a complex carbohydrate found in many foods, such as grains, fruits and vegetables, and there are several forms.
So that we can use starch as a source of energy, we must destroy it, “a bit like we destroy words in letters,” illustrates May Faraj. The more it is hydrolyzed into small letters, the more it can be absorbed.”
“Resistant” starch is a starch that is not hydrolyzed very well, explains the researcher. It therefore passes the stomach, the small intestine and reaches the colon. And it is the microbiome (intestinal bacteria) that uses it, producing a new form of energy – fatty acids. Resistant starch actually gives the body less energy. “For example, instead of four calories per gram of glucose, you can have maybe two calories when it’s hydrolyzed by the microbiome,” explains May Faraj.
By cooling and reheating pasta or pizza, we could transform a little starch into resistant starch, agrees the professor. “Because it forms a gel, which means that the enzymes in the intestine cannot hydrolyze the carbohydrates,” she popularizes. “But is the amount of change and the physiological effect going to make a difference for someone who has diabetes or for someone who wants to lose weight? Does it improve blood sugar? Does it provide any health benefits? No. »
Doctor and presenter Alexander van Tulleken likely based his argument on a handful of small studies published in the last 10 or 15 years. These studies showed that cooling rice and other starchy foods might reduce the effect on blood sugar, but not always. In 2021, nutrition researchers from the University of Toronto published a serious clinical study in a reputable journal. They concluded that cooling cooked rice did not reduce the glycemic index or starch digestibility.
Consult the study
“For a discovery to change clinical practice, there must be ample evidence of the benefits of randomized clinical trials and other types of studies conducted by different research groups,” says May Faraj. The risk of spreading this type of statement, she says, is that people with diabetes put them into practice believing that they are controlling their blood sugar levels.
The advice for slowing down glucose absorption remains the same: favor whole and less refined foods, opt for whole grains and legumes (which naturally contain resistant starch!), increase your consumption of fiber, vegetables, of fruit, eating enough protein and good fats at meals… “All of this is quite a bit more important than warming up the starch,” concludes May Faraj.