If you find yourself underweight, you should first check whether it is the potential influence of diseases, such as thyroid, diabetes, adrenal gland and digestive system diseases, which may easily lead to underweight. Only when the disease is eliminated can the fattening plan be implemented. If you eat enough protein, you should eat more foods rich in fat and carbohydrates (starch, sugar, etc.). In this way, excess energy can be converted into fat and stored under the skin, making the thin body strong. If the gastrointestinal function is weak, you can choose chicken, duck, fish and sheep liver to eat. In addition, fish is easy to digest and absorb.