Heating and cooling starchy foods (potatoes, pasta, barley, rice, beans...) can convert a small amount of starch into resistant starch, which cannot be digested in the small intestine but can be fermented by normal intestinal microbes in the large intestine.
There are 4 types of resistant starch, the one produced during food cooking and cooling is type 3 (RS3).
The nutritional characteristics of RS3:
- RS3 is not digested into glucose, so it does not raise blood glucose levels after meals (Harvard.edu).
- RS3 is fermented into short-chain fatty acids and some other nutrients, which are absorbed in the large intestine, have some nutritional value and may have some beneficial effects on the intestinal lining and the growth of intestinal flora (Institute of Food Technologists).
- Fermentation of RS3 results in a lower calorie value of absorbable nutrients (~2 Cal/g) than digestion of starch (~4 Cal/g) (EJCN).
- The fermentation of RS3 also yields gas that may cause some bloating and flatulence.
Cooling the food after cooking converts only 1-2% of starch into RS3 ( Harvard.edu, ACS.org). This means that the effects of resistant starch (lowering calorie value and glycemic index of the food) will be only small.
There is insufficient evidence to say that high consumption of resistant starch is effective in weight loss, lowering glucose or cholesterol levels, improving intestinal flora or prevention of diabetes or colon cancer (Advances In Nutrition, AJCN).