Lipids in normal tissues of human body account for 14%~ 19% of body weight, mainly distributed under the skin and around internal organs, and most of them are stored in adipose tissue in the form of triacylglycerol. Most of the fat is ingested from food. When the sugar and protein in food are ingested too much, it will be converted into fat and stored. Studies have confirmed that obesity gene is only expressed in adipose tissue, and its gene product is leptin, which is the key factor to control weight stability and energy balance. Leptin is synthesized in adipocytes and secreted into the blood, which acts on the central nervous system through the blood-brain barrier, inhibits food intake, increases the body's heat production, and finally plays a role in losing weight and lowering blood fat.

When the exercise intensity is lower than 70% of the maximum oxygen uptake, and the continuous exercise time is 40, 90, 180 and 240min respectively, the activity of sympathetic adrenergic system increases, the secretion of glucocorticoid increases, and the plasma glucocorticoid concentration increases. Glucocorticoid can inhibit insulin secretion and reduce plasma insulin concentration. When the exercise intensity reaches 50%~70% oxygen uptake, the excitability of sympathetic adrenergic system is obviously improved, and the plasma concentrations of adrenaline and norepinephrine are also obviously increased. On the one hand, the body stimulates β -adrenergic receptors, improves the activity of hormone-sensitive lipase, and strengthens fat mobilization and fat decomposition to meet the needs of increasing energy consumption during exercise. On the other hand, by reducing the concentration of plasma insulin, the anti-lipolysis effect of plasma insulin is weakened, while the lipolysis function is enhanced. The activities of plasma insulin, glucocorticoid and sympathetic adrenergic system all affect the expression of obesity gene and promote the synthesis of leptin, thus playing a more effective role in reducing weight and lipid.

Insulin plays an important role in energy balance and weight regulation. Long-term use of insulin in the periphery will lead to the increase of body fat, while using a small amount of insulin in the center (ventricle) will suppress appetite, reduce food intake, increase heat production and lose weight. Experiments show that systematic aerobic exercise can significantly improve the insulin level in cerebrospinal fluid and hypothalamus. Aerobic exercise can promote the synthesis of brain neurons and release insulin. The increase of insulin concentration in cerebrospinal fluid is related to the increase of insulin content in hypothalamus. Because insulin in cerebrospinal fluid can reduce food intake, lose weight, improve body heat production and increase energy consumption, exercise-induced weight loss is related to the increase of insulin content in cerebrospinal fluid and plays an important role in exercise-induced weight loss.