Diabetes mellitus is a chronic metabolic disease with elevated blood glucose. The typical symptoms of diabetes mellitus are three more and one less, namely polyphagia, polyuria and polyphagia with wasting. Diabetic patients are very thin for the following reasons: 1. Insulin deficiency is serious, insulin is a pro-synthetic hormone that can promote the synthesis of protein, fat and glycogen and inhibit the breakdown of protein, fat and glycogen. When insulin deficiency is severe, the pro-synthetic effect will be weakened and the catabolism will be enhanced leading to wasting. 2, excessive blood sugar, when blood sugar is elevated significantly, a large amount of glucose is excreted from the urine, the carbohydrates available to the body are reduced, and only fat decomposition can be used for energy, leading to wasting. 3, taking metformin, some patients taking metformin will experience weight loss. 4, too strict dietary control, when Diabetic patients with overly strict dietary control, long-term caloric intake will appear when the weight loss.