Obesity is a state caused by excessive accumulation of body fat, especially triglycerides. Usually, excessive food intake or changes in body metabolism lead to excessive fat accumulation in the body, which leads to excessive weight gain and pathophysiological changes in the human body.

Body mass index (BMI) is the square of weight (Kg) divided by height (m), which is an index to evaluate the degree of obesity.

In Europe and America, the body mass index ≥25kg/m2 is overweight, and the body mass index ≥30kg/m2 is obesity. According to the different body mass index, the population in the Asia-Pacific region can be divided into: healthy18.5-22.9 kg/m2; Overweight 23-24.9 kg/m2; 1 degree obesity 25-29.9 kg/m2; Second-degree obesity is 30-34.9 kg/m2; Third-degree obesity > 35kg/m2.

Obesity can be divided into simple obesity and secondary obesity. Simple obesity has no clear cause, which may be related to heredity, diet and exercise habits. It can also be called primary obesity in medicine. In all obesity, more than 99% is simple obesity. The exact pathogenesis of this obesity is still unclear.

As long as any factor can make energy intake exceed energy consumption, it may cause simple obesity. These factors include age, overeating, too little physical activity, social and psychological factors, genetic factors, adipose tissue characteristics and so on. Secondary obesity refers to obesity caused by other diseases.

The proportion of secondary obesity in obesity is only 1%. According to the causes of obesity, secondary obesity can be divided into hypothalamic obesity, pituitary obesity, hypothyroidism obesity, obesity caused by Cushing syndrome, hypogonadism obesity and so on. It is caused by diseases of hypothalamus, pituitary gland, thyroid gland, adrenal gland and gonad respectively.