SIt seems like one of the tricks circulating on the internet: if you eat potatoes after letting them cool, you will have benefits for your blood sugar and intestines, perhaps your weight and general health. A praise of leftovers that appears even more unlikely if connected to potatoes, which have been shrouded in bad fame since their arrival in the Old Continent, with the voyages of Columbus. Underground expressions of the plant, dirty. As late as 1751, Diderot and D’Alembert defined them as “tasteless and floury”, in an entry that was certainly not celebratory of the first edition ofEncyclopédie.
It is hard to believe that the thesis according to which the change in temperature of the tubers benefits the body is scientific. Nevertheless a change actually occurs in starchy foods, including rice and pasta with cooling: a type of starch is created which is indigestible.
And this starch, defined as resistant because it resists digestive enzymes, it remains almost intact even if you heat the dish again. For example, if we make an omelette with spaghetti or potatoes prepared the day before.
The benefits of resistant starch
The explanation concerns biochemistry and is easy to understand. We make starch, which is the main energy reserve of plants, edible only by cooking. In fact, cereals are inedible raw and must be softened.
But if we let potatoes or rigatoni rest, a part of the starch that had gelatinized with the water and the heat undergoes a retrogradation, that is returns to a structure similar to the original one. Instead of being soft, it is rigid, crystallized. That fraction of resistant starch (in the acronym Rs, Resistant Starch) it cannot be broken down by enzymes and absorbed at the end of digestion, but will reach the large intestine intact.
Starch is found in many foods, such as rice, pasta, potatoes and legumes (photo Getty Images)
Two consequences arise from this. The first is that we don’t assimilate all the glucose which forms the carbohydrate chains of starch: it means that the sugar potential of the tuber or rice dish decreases and that the glycemic index is lowered, i.e. the speed with which glucose ends up in circulation, raising its levels in the blood ( blood sugar).
The second result is that resistant starch behaves like dietary fiber. Having reached the intestine where the microbiota is located, the population of microorganisms that was once called bacterial flora, selectively nourishes the good bacteria. These thrive, at the expense of bad strains, and produce short-chain fatty acids, including butyrate, which protect the intestinal walls and are linked to a reduction in inflammatory states.
In medical terms, it is said that resistant starch has a prebiotic effectbecause it is fermented by probiotic bacteria, our friends, which in turn release postbiotics, very important substances for human health.
According to some studies, the cascade action of resistant starch could improve insulin sensitivity, influence hunger and satiety hormones and reduce abdominal fat. A work just appeared on Cell Metabolism it also shows excellent results in non-alcoholic steatohepatitis, reducing triglycerides inside the liver.
For problematic intestines
Another important consideration concerns people who suffer from problems such as irritable bowel syndrome: their insufficient intake of fibre, which causes gas and bloating, can be compensated for by resistant starch.
For example, it was recently formulated the exclusion diet for patients with Crohn’s disease in the acute phasethe chronic inflammatory pathology of the digestive system: in the first phase a series of foods that could be harmful are eliminated, while every day it is mandatory to eat cooled potatoes, in order to rebuild the favorable population of microbiota and rearrange the colon damaged by the reaction autoimmune.
The similarities with fiber
Dietary fiber, a prerogative of plant sources, has been linked to a reduction in the risk of heart disease, type 2 diabetes and some forms of cancer. It seems that similar advantages can also be offered by resistant starch, as emerges in a review of the most reliable studies on the subject, signed by Polish researchers (on Journal of Functional Foods 2022).
There are foods that naturally contain resistant starch, such as legumesand supplements are on the market, which should be recommended by your doctor when you suffer from some pathology.
The easiest way to increase levels of the substance in foods such as pasta, potatoes and rice is to consume them as if they were leftovers: cooking and cooling them, to cook them again, if you like, or to eat them at room temperature. Among other things, it is an excellent anti-waste strategy.
Eliana Liotta (photo by Carlo Furgeri Gilbert).
Eliana Liotta is a journalist, writer and science communicator. On iodonna.it and on the main platforms (Spreaker, Spotify, Apple Podcast and Google Podcast) you can find his podcast series The good that I want.
The scientific review is by Amber Cilibertodietician in Milan at the gastroenterology division of the San Raffaele hospital and at the Galeazzi – Sant’Ambrogio hospital.
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