When it comes to obesity, it is thought that there is an excess of nutrients and excess calories are converted into fat deposits in the body, causing weight gain. In fact, obesity is not an overall excess of nutrients, but many nutrient deficiencies. A study showed that among 379 obese patients, iron deficiency accounted for 43.9%, hemoglobin deficiency accounted for 8.4%, thiamine deficiency accounted for 29%, and vitamin D deficiency accounted for 68.1%. We recently studied a group of obese people and found that 91% were vitamin D deficient. Then there are nutrient deficiencies such as folic acid, iron and zinc. The lack of these nutrients affects the normal metabolism of the obese group. The causes of nutritional imbalance in obese groups are multiple, including problems with diet structure and lack of outdoor activity. Weight loss surgery has some impact on nutrient metabolism after bariatric surgery. Commonly used bariatric surgery modalities include gastric bypass surgery and gastric sleeve resection. In the former, the stomach below the esophagus is disconnected and then anastomosed with the intestine. Food does not pass through the stomach and goes directly to the lower intestinal tube. In the latter, the stomach is removed longitudinally without altering the continuity of the digestive tract. 86 postoperative nutritional status changes in patients undergoing bariatric surgery were studied by Coupaye, who underwent gastric bypass and gastric sleeve resection, respectively. Despite the fact that 90% of post-surgical gastric bypass patients took multivitamin preparations, their vitamin B12, vitamin D, and calcium concentrations were significantly lower than those of patients who underwent gastric sleeve resection. We studied the changes in nutritional status after gastric sleeve resection and found that all trace elements were normal after surgery. Vitamin D rose almost to normal levels. This suggests that gastric sleeve resection has a much milder effect on postoperative nutrition. Hair loss after bariatric surgery is very common. Our recent study found that most hair loss occurs in the third to fourth month after surgery. This time is often accompanied by significant weight loss. Hair loss tends to improve naturally within six months of its occurrence. Attempts to treat hair loss with various nutrient supplements are often ineffective. The causes of hair loss after weight loss surgery are not well understood. The likely cause is related to rapid weight loss. This is when there is a rapid loss of fatty tissue throughout the body and a decrease in body thickness. The same changes occur in the scalp. The scalp becomes thinner and cannot support the hair, which can cause shedding. Men have shorter hairs, so men lose much less hair than women. After a few months the tissue structure of the body surface stabilizes and the hair grows back.