Analysis: 1, excessive exercise, whether it is mental work or manual work, as long as it is too large, it will not gain weight, and mental work sometimes causes hair oil or hair loss; 2, the amount of food eaten, if the calories provided by eating are less than the output of exercise calories, this is a popular way to make ends meet, so it will not be fat. If this situation lasts too long, it will pose a great threat to health; 3. Digestion and absorption. If there is something wrong with your system, it's no use eating more. 4, genetic factors, if there are no obese people in your family, then your friends may not be as slim as your family. In addition, Rosso said, what does it matter if you are fat or thin, as long as you are healthy.