Clinically, thinning legs may be caused by malnutrition. Because in malnutrition, the patient will gradually break down the body fat for energy consumption, so the patient will lose weight and the legs will look thinner and thinner. In addition, diseases can also cause wasting, such as diabetes. If you have a family history of diabetes or like to eat sweet things, and you are over 40 years old, you may have hyposecretion of insulin or insulin resistance to produce diabetes, which will cause you to lose weight and your legs will become thinner. In addition, it is not excluded that the legs become thinner due to lack of exercise, that is, costal muscle atrophy, which is mostly seen in patients who are bedridden for a long time, and will recover through exercise.