How to eat without gaining weight may be the result of more exercise, gastrointestinal indigestion or tumors, or metabolic diseases. Exercise more will lead to high energy consumption, there will be little fat hoarding, and you will not gain weight. When the gastrointestinal tract has inflammation or lesions will affect the digestive capacity of the gastrointestinal tract, food can not be well decomposed after entering the gastrointestinal tract, less nutrition is absorbed into the body, and less energy is supplied to the body’s activities, so there will not be excess energy storage, even if you eat more, you will not gain weight. Metabolic diseases mainly include tumors and diabetes. Patients with tumors have abnormal tissue growth in their bodies, which requires extra capacity to supply, and part of the nutrition eaten into the body has to be distributed to the tumor tissue, resulting in no excess fat and other energy storage, so they will not gain weight. Patients with diabetes and hyperthyroidism are in a state of disordered metabolic function, consuming more and metabolizing faster.