The body mass index of healthy adults (18 ~ 64 years old) in China should be between 18.5 ~ 23.9 kg/m2. Because people's weight includes the weight of body fat tissue and the weight of non-fat tissues such as bones, muscles and body fluids. Therefore, for most people, the increase of body mass index generally reflects the increase of body fat weight, but for people with a high proportion of muscles in the body, such as athletes, the range of body mass index of healthy weight may not be applicable. In addition, children and adolescents are in the stage of growth and development. In addition to weight and height, they can also be used as important indicators of development and nutritional status, and body mass index standards of different sexes and ages can also be used.
Being overweight or underweight is unhealthy. Being underweight generally reflects relatively insufficient energy intake, which easily leads to malnutrition. Overweight reflects relatively excessive energy intake or insufficient activity, which is easy to lead to overweight and obesity, and can significantly increase the risk of diseases such as type 2 diabetes, coronary heart disease and colon cancer. Food intake and physical activity are two main factors to maintain a healthy weight. Therefore, people of all ages should control energy intake and increase energy consumption to maintain energy balance and healthy weight.