Leftover rice reheated before eating, or leftover rice fried before eating ―― many people think this is both hygienic and economical. In fact, it's hard to digest leftover rice after reheating, and in the long run, it may cause gastritis. Let's take a look at how starch, the main component of rice, is digested and absorbed in the body. First, the salivary amylase in the mouth hydrolyzes starch into dextrin and maltose. Second, in the small intestine, pancreatic amylase and disaccharidase secreted by the pancreas continue to break down dextrin and maltose into monosaccharides for absorption by intestinal mucosal cells. When starch is heated above 60℃, it gradually swells and eventually becomes paste. This process is called "gelatinization." Human digestive enzymes can easily hydrolyze this gelatinized starch molecular structure. However, when the gelatinized starch cools down, the molecules rearrange themselves and expel water, producing a "retrogradation" phenomenon, which is called the "aging" of starch. Even if the aged starch molecules are reheated, no matter how high the temperature is, they cannot return to the molecular structure during gelatinization. The aging structural state of starch reduces the body's ability to hydrolyze and digest it. Therefore, long-term consumption of this cold-reheated rice can easily lead to indigestion and stomach problems. Therefore, the elderly, infants, or patients whose digestive functions have weakened, especially those with gastrointestinal diseases, had better not eat or eat less rice that has become cold and then reheated.