There are many reasons for not being fat: First, genetic factors. Thin people are inherited by their parents. Since childhood, they have a reasonable diet and a high level of energy metabolism, which leads to weight loss. Second, there is something wrong with gastrointestinal function. The biggest physiological reason may be that the gastrointestinal system is weak and the digestive system cannot function normally, leading to emaciation. Third, get sick. For example, suffering from endocrine diseases such as diabetes and hyperthyroidism will lead to incomplete nutrient absorption, which is more common. Fourth, it has something to do with peacetime exercise. One of the secrets of not being fat is to love sports. Although thin people eat a lot, they exercise a lot every day. Fifth, the diet structure is different. Some people like to eat fruits and vegetables, but the calories are not necessarily high. Because these foods are low in calories, eating these foods is not easy to cause obesity. Sixth, it is related to emotions. When you are happy, you will eat more, and when you are angry or in a bad mood, you will not eat, even for a day. Seventh, the basal metabolism is high. The reason for not being fat for a long time may be that the basal metabolic level is relatively high. The higher the level of energy metabolism in the body, the more capacity the human body consumes. Eight, the schedule is too messy, don't sleep all night, sleep during the day. Usually irregular work and rest, leading to eating fat.