The biggest physiological reason for not being fat may be that the gastrointestinal system is weak, the digestive and absorption system can't exercise normally, and the food eaten is excreted before being digested, so it is naturally not fat. Such people have weak physique and low immunity, and are actually in a sub-healthy field. Another reason is that people's physique is greatly influenced by the genetic factors of father and mother. Thin people are inherited by their parents or get reasonable dietary nutrients from childhood, and their energy metabolism level is high, and the human body consumes more energy. Many practical situations clarify that people who have exercised more since childhood have higher muscle content, higher basal metabolism and more energy consumption. People with high basal metabolic rate, even if they lie still in bed, their bodies will help them consume more calories. Exercise can help improve basal metabolic rate and regulate physical fitness. Some people eat many vegetables and fruits, but the calories are not necessarily high, because the calorie content of these foods is relatively low; Some people eat very little. She eats cakes, pizzas, ice cream ... The calories are naturally low. Different dietary structures provide different nutrients and calories to the body.