1. Hereditary thinness: If all family members are thin, underweight may be hereditary, and the natural metabolic rate is high, even if they eat too much, they will not get fat.
2. Environment-driven: Work stress, noisy eating environment and unpalatable food may affect appetite, leading to insufficient food intake.
3. Overconsumption: People who consume more may also be the reason for being thin.
For every 3,500 calories your body consumes, you gain a pound. For example, if a person who eats 2000 calories a day wants to gain weight, his daily calories will increase to 2500 calories, and he will gain a pound in a week. You can Baidu about "Li Yun's fattening experience". There are detailed methods, I hope I can help you.