The fatness of the human body is affected by many reasons, such as food sources, appetite regulation, disease factors, etc. In the case of adequate food sources, appetite regulation is an important factor affecting body weight, that is, obese people generally have a better appetite, while lean people have a poorer appetite. Medical can use leptin sensitivity to explain, leptin is adipose tissue produced by the regulation of appetite hormone, fat increased leptin production increased, acting on the hypothalamus appetite center, produce anorexia effect. Obese people are less sensitive to leptin, while lean people are more sensitive to leptin, and a small amount of leptin can produce a strong appetite suppressant effect. Factors of disease, including digestive tract diseases, such as gastritis, gastric ulcer, cholecystitis, pancreatitis, chronic enteritis, etc., may affect eating and food absorption, resulting in wasting. Hyperthyroidism can cause a high metabolic state and increased calorie consumption can lead to overeating and wasting, while type 1 diabetes can also cause wasting due to insufficient insulin secretion and inability to convert glucose into fat. In addition, tumors often occur with more rapid weight loss.