You know why. I’ve been writing about it for years. Happens also to pasta.
Influence Of Resistant Starch Resulting From The Cooling Of Rice On Postprandial Glycemia In Type 1 Diabetes, Nutrition and Diabetes, 16 April 2022
Each participant of the study consumed two standardized test meals consisting of long-grain white rice. One of the test meals was served immediately after preparation, and another was cooled for 24 h at 4 °C [about 40 degrees F, refrigerator temp] after preparation and reheated before being served.
Conclusions: Consumption of rice subjected to the cooling process results in a lower increase of postprandial blood glucose in subjects with type 1 diabetes.
So, a delayed blood glucose peak, and a lower peak. Why? Resistant starch:
The cooling of rice after cooking causes retrogradation of starch, which becomes a non-absorbable product in the human digestive tract.
Note that the rice was reheated after being cooled. It did not substantially lessen the resistant starch formed during cooling. Also, “multiple heating/cooling cycles of starch products increased the resistant starch content even more.”
These resistant starch calories are, by the way, calories we do not absorb.
It is believed that the content of resistant starch in the diet has a beneficial effect on reducing the degree of hunger and the desire to eat and increasing the feeling of fullness.*
* Type-4 Resistant Starch in Substitution for Available Carbohydrate Reduces Postprandial Glycemic Response and Hunger in Acute, Randomized, Double-Blind, Controlled Study, Nutrients, February 2018