Obesity is a clinical syndrome characterized by a body mass index (BMI) exceeding normal levels. Generally, obesity with an unclear cause is called simple obesity, or primary obesity, while obesity with a known cause is called secondary obesity. In China, the standards for BMI are as follows: a normal BMI is below 24 kg/m². Being overweight is defined as having a BMI greater than 24 kg/m², mild obesity is greater than 26 kg/m², moderate obesity is greater than 28 kg/m², and severe obesity is greater than 30 kg/m². Therefore, obesity is a metabolic clinical syndrome.