First, the thin constitution is mainly due to the poor digestion and absorption function of the spleen and stomach, which is a manifestation of weakness of the spleen and stomach, so we should start with conditioning the spleen and stomach. You can take some Chinese patent medicines such as Ginseng Jianpi Pills. Choose some foods rich in protein and nutrition. Don't be picky about food, eat more fresh fruits and vegetables. Besides, have a good sleep and don't stay up late. Don't gain weight by eating junk food, it's harmful to your health.