The early stage of hypothyroidism is not necessarily fat, but hypothyroidism that has not been treated in time for a longer period of time will generally gain weight and become fat. Hypothyroidism fat is mainly caused by edema, its causes are mainly the following aspects: First, hypothyroidism patients are not treated, the reduction of thyroid hormone in the body will cause urine from the kidneys to reduce, resulting in water and sodium retention; Second, hypothyroidism patients in the body capillary permeability increased, the blood protein components, especially mucin, will penetrate into the tissue interstitial deposition, while mucin will take away water and sodium from the blood in The patient will have generalized swelling, especially eyelid and facial swelling; Third, thyroid hormone can promote the decomposition of protein, lipid and carbohydrate to produce heat, so when hyperthyroidism has too much thyroid hormone, it will lead to weight loss; on the contrary, the decrease of thyroid hormone synthesis and secretion causes hypothyroidism, which will lead to the decrease of protein, lipid and carbohydrate decomposition, and thus weight gain.