It turns out that people's hunger and satiety are controlled by the human brain. In human hypothalamus, there are nerve centers that control appetite, which are divided into satiety center and feeding center. Glucose and free fatty acids are substances that stimulate these two centers. When the glucose in the blood increases after eating, the satiety center is stimulated and excited, and people feel full and don't want to eat any more. When glucose in the blood decreases, the body decomposes fat to supply energy, which increases free fatty acids in the blood, stimulates the feeding center and produces hunger.

Simple obesity can be caused by the increase of the number of adipocytes, the increase of adipocytes or the increase of intracellular fat content. Obesity in children is mostly due to the increase in the number of fat cells, which can reach 3-4 times that of normal children. At the same time, fat cells can be enlarged to varying degrees, and the intracellular fat content is also increased. Obese people usually have higher plasma concentrations of insulin, fatty acids, triglycerides and amino acids. It may be because the tissues of obese children are resistant to insulin, which leads to hyperinsulinemia, which leads to the synthesis of triglycerides in the liver and the increase of cell number. At the same time, the increase of insulin, triglycerides and free fatty acids in the blood constantly stimulates the feeding center, so fat babies always feel hungry, leading to overeating. The result is that the more you eat, the fatter you get, and the more you eat, the vicious circle.