Appetite good but still thin may be exercise and other physiological reasons caused by fast metabolism, or eat food low calorie caused, there may be gastric ulcer and other diseases caused by poor digestion and absorption of food, hyperthyroidism, diabetes and other body metabolism level and other high causes. 1. If the metabolism is accelerated due to physiological reasons such as regular exercise, the situation of having a good appetite but being thin may also occur. Good appetite but low calorie intake can not meet the body’s consumption, so still thin. You should pay attention to adjusting your diet, and eat more fatty foods such as doughnuts and mutton, which can increase calories and be able to gain weight. 2. Gastric ulcer and other digestive system diseases, food is not fully digested and absorbed out of the body, poor digestion and absorption, so it will be thin. Hyperthyroidism patients due to excessive secretion of thyroid hormones, the body’s metabolic level is high, physical energy consumption, so appetite but not fat. Diabetic patients due to sugar metabolism disorder, the body cells can not get enough sugar energy, will also appear the phenomenon. Appetite but still thin may also be other reasons, excluding diet and other physiological reasons, you should consult a doctor in a timely manner to clarify the cause of the disease, under the guidance of the doctor for treatment, so as not to delay the condition.