Obesity has become a widespread health problem worldwide. In the United States, overweight and obese adults account for 65%, about 130 million, and 400,000 people die of obesity every year. In China, with the improvement of living standards, the proportion of obesity is increasing year by year. According to China’s nutrition and health status survey published, overweight and obese people more than 280 million people, has been close to the total population of 1/4; of which overweight people for about 215 million people, obese people for about 68.44 million people. Obesity has become an epidemic in most developed and developing countries. As the severity of obesity rises, the incidence of diabetes, hypertension, dyslipidemia, coronary heart disease, myocardial infarction, stroke, breast cancer and many other types of cancers increases significantly, and the mortality rate rises greatly. It is recognized by the World Health Organization as the fifth major risk factor affecting health. At present, the treatment of obesity includes both surgical and non-surgical treatments. Non-surgical treatments include dietary control, increased exercise, lifestyle changes, and medication. These non-surgical treatments are only suitable for overweight and mildly obese people, and the effect of treatment lasts for a shorter period of time. Weight loss from low-calorie diets usually rebounds within 2-4 years. Theoretically, exercise with dietary control can provide long-lasting weight loss. However, it is often difficult for patients to adhere to it for a long period of time. Lifestyle changes have little long-term effect. Medication is poorly effective in the treatment of severe obesity. For severely obese patients, surgical treatment is the only long-term effective way. Moreover, most severely obese patients with diabetes mellitus, hyperlipidemia, hypertension, and other co-morbidities are completely or partially relieved after surgery. Severe obese patients require surgical treatment. Body mass index [BMI = weight (kg)/height2 (m)] is the basic basis for judging whether surgery is necessary. In Europe and the United States, severe obesity, i.e., BMI ≥40 or BMI ≥35 complicated by one or more obesity-related serious health problems, is considered to be an option for surgical treatment [5]. However, due to ethnic differences, a lower BMI in Asians can create serious harm. Therefore, the criteria for surgery in Asia are BMI ≥37 or BMI ≥32 complicated by one or more obesity-related serious health problems. In addition, abdominal obese individuals with large waist circumferences (>88 cm for women and >102 cm for men) are at greatly increased risk for diabetes, hypertension, hyperlipidemia, cardiovascular disease, and other diseases. Therefore, obese patients with large waist circumference, even if the BMI is not high, should be considered to have surgical indications. In addition, must also be excluded due to drugs, endocrine causes of secondary obesity and the existence of serious psychological behavioral disorders. 2.Surgery Various bariatric surgery is mainly based on the two basic principles of restricting intake and reducing absorption to achieve. With the development and application of laparoscopic technology, most of the bariatric surgery can now be performed under laparoscopy. This reduces surgical trauma, postoperative pain, and hospitalization time for patients, and postoperative recovery is faster 1.1 Laparoscopic Adjustable Gastric Banding (LAGB) Laparoscopic separation of the omentum and fat from the lateral aspect of the greater and lesser curvature exposes the right diaphragmatic pedicle. Starting below the esophagus and superficial to the right diaphragmatic pedicle, the posterior wall of the stomach was separated in the direction of the cardia incision to create a retro-gastric access into which a silicone band with adjustability was placed. The ends of the band were docked and fastened to close the loop around the stomach. The stomach wall is sutured above and below the band to secure the band and prevent slippage. The attached regulator pump is secured under the abdominal wall. After the surgery, a 10-15 ml gastric pouch is formed above the band, which produces a feeling of fullness when food enters the pouch, thus reducing the amount of food intake and thus achieving weight loss. At the same time, the surgery does not destroy the structure and function of the stomach, and when the desired weight loss result is achieved, the band can be removed and the stomach can be restored to its original state. As a purely volume-restricting surgery, LAGB has now replaced Vertical Banded Gastroplasty (VBG) due to its advantages of minimal damage, safety and effectiveness, adjustability and recoverability. LAGB is safer than other surgical procedures and is indicated for obese individuals over 55 years of age. However, it is inferior to Roux-en-Y gastric bypass and biliopancreatic bypass in terms of long-term weight loss. Important complications of this procedure are: slippage of the band, erosion of the band, and esophageal dilatation. 1.2 Roux-en-Y gastric bypass (RYGB) is the most commonly performed bariatric surgery in the United States today. RYGB provides better weight loss than simple gastric restriction surgery; comparative studies have shown that laparoscopic RYGB provides the same weight loss as open RYGB, but with fewer postoperative complications and pain. The upper part of the stomach is transected laparoscopically, and the proximal gastric pouch of about 10-30 ml is divided.The jejunum about 30 cm below the ligament of Triez is transected, and the distal end forms a long arm (digestive collaterals), which is lifted up and anastomosed to the gastric pouch; the proximal end is closed, and a short arm (biliopancreatic collaterals) is formed, which is anastomosed with the long arm of the jejunum at the side of the line. The large distal portion of the stomach, the duodenum, and a small portion of the starting segment of the jejunum are shunted and functionally obsolete.The RYGB reduces nutrient absorption by shunting based on a restricted food intake. The standard RYGB has a long arm (digestive collaterals) of about 80-120 cm and is more suitable for obese individuals with 4050, the long arm (digestive collaterals) needs to be at 150cm, known as a long arm RYGB procedure. 1.3 Biliopancreatic diversion with duodenal switch (BPD/DS) Biliopancreatic diversion (BPD) achieves weight loss by limiting the volume and massively reducing absorption. Laparoscopically, the stomach is first subtotally resected, the volume of the preserved proximal stomach is about 200-500 ml, and the duodenal dissection is closed. The small intestine was cut off at 250cm from the ileocecal valve, and the distal end was anastomosed with the proximal stomach; the proximal small intestine and ileum were anastomosed at 50cm from the ileocecal valve. In this way, the biliary and pancreatic digestive juices in the proximal small intestine only act in the last 50cm of small intestine, reducing the effective absorption of food. Postoperative weight was greatly reduced and abnormalities of fat and glucose metabolism were improved. However, there are more postoperative complications such as steatorrhea, dumping syndrome, and malnutrition. In order to minimize the complications, Hess et al. modified the procedure and proposed Duodenal switch (DS). Sleeve gastrectomy was performed first and the duodenum was cut at the pylorus with the distal duodenum left open. The ileum is isolated 250 cm from the ileum, the distal small intestine is anastomosed end to end with the proximal duodenum, and the proximal small intestine is anastomosed end to end with the ileum 100 cm from the ileum.BPD-DS increases the effective absorption of food and reduces complications such as malnutrition.Laparoscopy was first used in 1999 for BPD/DS, which has reduced the incidence of surgical trauma and complications. This surgery is relatively complex and difficult to operate, with relatively more complications and dangers, but the effect of weight loss is significantly better than other types of surgery. 1.4 Staged Bariatric Surgery For some high-risk obese patients, in order to reduce the risk of surgery and postoperative complications, the surgery should be chosen to be staged. In the first stage, patients first undergo sleeve gastrectomy to restrict food intake. This procedure results in a 33%-45% reduction in excess body weight in the first postoperative year [18]. At one year postoperatively, after significant weight loss and a decrease in surgical risk, a second-stage RYGB or BPD/DS procedure is feasible. In a prospective study, sleeve gastrectomy was performed on 126 obese patients with a mean BMI >65 and multiple obesity-related diseases, and the patients lost an average of 46% of excess body weight after surgery, with a perioperative mortality rate of 0 and a major complication rate of only 8%. Therefore, for high-risk patients, sleeve gastrectomy can be the first choice for phase I surgery. 3.Major complications and mortality rate The most common adverse reactions to limited capacity surgery are mainly gastrointestinal reactions, such as nausea and vomiting, with an incidence rate of 50%. After shunt surgery, the incidence of dumping syndrome is higher, at about 70%. Malnutrition is more common after malabsorption surgery, such as iron, calcium, folate, and VitB12 deficiencies. These complications are mild and can be improved with proper diet and life management [20]. The major complications of surgery are venous thrombosis, anastomotic leakage, wound infection, bleeding, incisional hernia and small bowel obstruction. In the Swiss obese subjects (SOS) showed a 13% incidence of major postoperative complications, including bleeding 0.5%, embolism 0.8%, wound complications 1.8% and pulmonary complications 6.1%. A series of large studies have shown a mortality rate of 0.1%-2.0% for bariatric surgery. A retrospective analysis showed mortality rates of 0.1% for gastric banding, 0.5% for bypass surgery, and 1.1% for malabsorption surgery. The main causes of death were pulmonary embolism and anastomotic leakage. Inadequate surgical experience, older patient age, severe obesity (BMI >50), and patient underlying disease all increase surgical mortality. To better evaluate the morbidity and mortality associated with bariatric surgery, the National Institutes of Health (NIH) conducted a 3-year (2005-2007) multicenter, prospective Longitudinal Assessment of Bariatric Surgery (LABS). Bariatric Surgery (LABS). This study showed that with advances in technology and experience, the risks of bariatric surgery have been greatly reduced and are not even higher than the risks of gallbladder surgery. The risks associated with surgery are much lower than the long-term risk of dying from heart disease, diabetes, and other obesity-related diseases. The overall 30-day postoperative mortality rate was only 0.3%, with 0% for patients undergoing LAGB, 0.2% for LRYGB, and 2.1% for open RYGB surgery; 4.3% of patients experienced at least one surgical complication. Bariatric surgery is safe, cost-effective, and efficient, dramatically reducing office visits and medication and other medical expenditures. 4. Improvements brought about by surgery Severe obesity affects every organ in the body. Surgery can effectively reduce the weight of obese people, and at the same time make a variety of obesity-related diseases get relief, such as type 2 diabetes mellitus (T2DM), heart disease, high blood pressure, hyperlipidemia, respiratory dysfunction, polycystic ovary syndrome, and psychological problems. 4.1 Weight Loss Surgical procedures significantly and effectively reduce patient weight over time. The results of the SOS program, a large case-control study, showed that at 2 years postoperatively, the average weight loss was 32% for patients who underwent gastric bypass surgery and 20% for patients who underwent gastric banding. 25% and 14% respectively at 10 years postoperatively [14].A retrospective analysis conducted by Buchwald et al. showed that all types of bariatric surgery were effective in reducing excess weight (Excess weight loss, EWL).47.5% for LAGB, 61.6% for RYGB and 70.1% for BPD/DS. 4.2 T2DM The development of diabetes mellitus, especially type 2 diabetes mellitus, is closely related to obesity. 60% of obese people have abnormal glucose metabolism. Surgical treatment, especially after RYGB and BPD/DS, resulted in significant relief of hyperglycemia.Buchwald et al. retrospectively analyzed a large amount of clinical data and showed that 86.6% of obese combined diabetics had diabetes remission or recovery after bariatric surgery. Among the various types of surgery, BPD/DS had the most pronounced remission, followed by RYGB and LAGB. rapid blood glucose levels return to normal after surgery when no significant weight loss has yet occurred. Patients who were treated with insulin preoperatively experienced a significant reduction in insulin dosage postoperatively, and the vast majority of patients were able to suspend insulin use six weeks postoperatively. Additionally, studies have found that diabetes control after bariatric surgery is effective over the long term. Diabetes remission after bariatric surgery is not only related to postoperative weight loss, but also to a series of postoperative gut endocrine hormone changes. In addition, numerous studies have shown that bariatric surgery has a preventive effect on diabetes. In a longitudinal study, LAGB was shown to significantly improve insulin resistance and metabolic syndrome in obese individuals. long et al. reported that patients with high preoperative blood glucose who underwent RYGB surgery had a 30-fold reduction in the risk of developing type 2 diabetes. The incidence of postoperative metabolic syndrome was also significantly reduced. In contrast, patients who underwent BPD surgery had normal insulin levels at 6 months postoperatively and exceeded normal levels at 24 months postoperatively. 4.3 Cardiovascular Disease Hyperlipidemia is present in more than 70% of obese individuals and is characterized by an increase in fasting triglycerides (TG), low-density lipoproteins (LDL) and a decrease in high-density lipoproteins (HDL), a change that greatly increases the risk of coronary heart disease. Substantial improvements in lipid metabolic abnormalities are seen after bariatric surgery, and this effect is maintained for at least 5-10 years [25, 30]. These improvements in lipid metabolism are associated not only with weight loss after surgery, but also with improved insulin resistance after surgery. Similarly, hypertension as well as cardiac function can be significantly improved after bariatric surgery [4, 14, 20, 23]. Because of this change, the risk of coronary heart disease, cardiogenic shock, and peripheral vascular disease is significantly reduced after bariatric surgery. Cardiovascular events as well as myocardial infarction-related mortality are also greatly reduced. 4.4 Respiratory Diseases Obesity places a significant burden on the respiratory system, resulting in respiratory sleep apnea syndrome (Sleep apnea), obesity-related hypoventilation syndrome (Obesity-hypoventilation syndrome, OHS), and asthma. Sleep apnea is often completely cured or partially relieved after bariatric surgery [4, 31].OHS is mainly characterized by hypoxemia and hypercapnia. When combined with sleep apnea, it is collectively referred to as Pickwickian syndrome.OHS is associated with increased intra-abdominal pressure, diaphragmatic elevation, and decreased chest wall compliance. Chronic hypoxemia can cause pulmonary vascular remodeling, leading to pulmonary hypertension and even heart failure. Weight loss from bariatric surgery significantly relieves OHS symptoms and improves lung function. Asthma in obese patients will also be relieved with the relief of GERD after surgery. 4.5 Digestive diseases Gastroesophageal reflux disease (GERD) and nonalcoholic fatty liver disease (NAFLD) are some of the more significant GI problems faced by obese patients. after RYGB, due to the ability to return the gastric acid and bile to the esophagus, the gastric acid and bile from the esophagus can be returned to the esophagus. After RYGB, GERD symptoms are significantly relieved as the amount of gastric acid and bile that can flow back into the esophagus is significantly reduced. Many studies have demonstrated complete healing of Berrett’s esophagus after RYGB. This improvement is also seen with simple gastric restriction surgery. Weight loss from either gastric bypass or simple restriction surgery significantly reduces intra-abdominal pressure, which is responsible for the relief of GERD.NAFLD is present in 84% of morbidly obese patients, 20% of whom also have inflammation, and 8% of whom even have fibrosis. Weight loss after bariatric surgery can alleviate or cure these liver diseases. 4.6 Other diseases such as polycystic ovary syndrome, psychological disorders, and osteoarthropathy can be alleviated and cured to varying degrees after bariatric surgery. 5. Summary The treatment of obesity and related co-morbidities through surgery has become the mainstay of treatment for morbid obesity worldwide. Surgery has been shown to be an effective long-term treatment for morbid obesity in both experimental and clinical settings. Although there may be some risk associated with surgery, with the development of technology and experience, this risk has been reduced to a very low level. And as far as the long-term benefits of surgery are concerned, it is undoubtedly a safe, cost-effective and effective form of treatment. Surgery treats or alleviates obesity-complicated diseases while reducing weight, resulting in a significant reduction in long-term mortality from obesity-related diseases. It also reduces the consultation rate and medication and other medical expenditures of obese patients, which is of great benefit to both the patients themselves and the society. At present, the technology of bariatric surgery has been developed more mature, for obesity and related diseases is relatively clear relief. However, the mechanism of bariatric surgery still needs to be further researched. Meanwhile, the development of bariatric surgery in China is still in its infancy and still needs further development.