There is an old saying in China that "the heart is broad and the body is fat". Only with a good attitude can you gain weight smoothly. Therefore, if you are too thin and want to gain weight, you must adjust your mentality and keep a good mood every day. In this way, if you are in a good mental state and have a good appetite, you will eat more and more, and the purpose of gaining weight will be successfully completed. If you are depressed for a long time, it is difficult to gain weight. Being thin is a symbol of human aging. Many elderly people lose weight not because of fat loss, but because of the decline of muscle quality and function. This symptom of muscle degeneration is called sarcopenia. When people enter old age, with the increase of age, the secretion of sex hormones decreases, which makes the ability of muscle synthesis insufficient and the incidence of sarcopenia increases. It is reported that the incidence of sarcopenia is 5%~ 13% among people aged 60~70, and 1 1%~50% among people over 80. Excessive emaciation of the elderly may also be caused by disease. Nervous system diseases can lead to wasting diseases such as malnutrition, inflammation, infection and malignant tumor, which greatly increases the energy consumption of human body and causes emaciation.