Living habits or family inheritance. Living habits need to be adjusted through diet, and more meals must be forced every day. If you can eat and drink from an early age, but you are not fat and your family is thin, this is a genetic problem. If you are a body of this genetic type, your basal metabolic rate is extremely high, your muscle gain rate is very slow, and you can't eat fat. You are really desperate, but you also have advantages because of slow fat growth and low body fat. Since you can eat, you don't have to consider too many factors and care too much about the effects of high-fat foods. When you keep a good appetite for a long time, it will definitely have an effect, but it may come a little later than the average person. Because a thin man needs a big man, you have to get fat before you can start training. The human body needs to consume calories. When you consume more calories than you metabolize, you will definitely gain weight. Therefore, my advice to you here is that you must eat more every day. You don't have to eat too much for a meal, but you must eat a lot. We call it eating less and eating more. But you can't just eat, you must cooperate with exercise. Next, I'll introduce you to which sports to cooperate with. When our weight begins to rise, we should first focus on training several large muscle groups, such as chest, shoulders and back. When your muscles in these parts start to get stronger and stretch your clothes, your friends around you will definitely notice that your figure has begun to change. I suggest you start training with barbell bench press.