Metabolic and Bariatric Surgery

In 2022, the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) updated recommendations for metabolic and bariatric surgery to include patients with a BMI > 35 kg/m2 regardless of comorbidities and those with a BMI 30 to 34.5 kg/m2 with metabolic disorders. Comorbidities include the following:

The updated recommendations also specify that BMI thresholds should be adjusted in Asian populations and that patients with a BMI ≥ 27.5 kg/m2 should be offered surgery (1 Indications reference Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Metabolic and bariatric surgery is offered as part of a weight-loss program that usually includes

Contraindications include

The most common metabolic and bariatric procedures performed in the United States include

Procedures such as the vertical banded gastroplasty or adjustable gastric banding are rarely used. Bariatric surgeons should be familiar with historical procedures because surgical complications can develop at any time—months to years—after surgery (1 Procedures references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Despite a growing percentage of the population with obesity, metabolic and bariatric surgery remains underused. Fewer than 1% of patients who qualify for surgery have the procedure. Telemedicine has allowed greater access to preoperative consultation; nonetheless, overall rates remain low (2 Procedures references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Usually, minimally invasive techniques—either laparoscopically or robotically—are used, resulting in less pain and a shorter healing time than after open surgery. Traditionally, bariatric surgery has been classified as restrictive and/or malabsorptive, referring to the presumptive mechanism of weight loss. However, other factors appear to contribute to weight loss; for example, both RYGB (traditionally classified as malabsorptive) and sleeve gastrectomy (traditionally classified as restrictive) result in metabolic or hormonal changes that favor satiety and weight loss and in other hormonal changes (eg, an increase in insulin release [incretin effect]) that appear to contribute to the rapid remission of diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more .

After RYGB (particularly) or sleeve gastrectomy, levels of gastrointestinal hormones, such as glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), are increased, possibly contributing to satiety, weight loss, and remission of diabetes. Increased insulin sensitivity is evident immediately postoperatively, before significant weight loss occurs, suggesting that neurohormonal factors are prominent in remission of diabetes. A change in gut microbiome may also contribute to changes in weight after RYGB. Metabolic and bariatric surgery reduces risk of mortality caused by cardiovascular disorders, diabetes, and cancer.

Preoperative evaluation consists of

Extensive preoperative evaluation is not routinely necessary, but preoperative testing may be necessary based on clinical findings, and measures to control certain conditions (eg, hypertension) or reduce risk may be taken.

Perioperative risks are lowest when metabolic and bariatric surgery is done in an accredited center.

Complications include

These complications can cause significant morbidity, prolong hospitalization, and increase costs. Tachycardia may be the only early sign of anastomotic leak.

Later problems may include prolonged nausea and vomiting secondary to small-bowel obstruction Intestinal Obstruction Intestinal obstruction is significant mechanical impairment or complete arrest of the passage of contents through the intestine due to pathology that causes blockage of the bowel. Symptoms include... read more and anastomotic stenosis.

Nutritional deficiencies (eg, protein-energy undernutrition Protein-Energy Undernutrition (PEU) Protein-energy undernutrition (PEU), previously called protein-energy malnutrition, is an energy deficit due to deficiency of all macronutrients, but primarily protein. It commonly includes... read more , vitamin B12 deficiency Vitamin B12 Deficiency Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements. Deficiency causes megaloblastic anemia, damage... read more , iron deficiency Iron Deficiency Iron (Fe) is a component of hemoglobin, myoglobin, and many enzymes in the body. Heme iron is contained mainly in animal products. It is absorbed much better than nonheme iron (eg, in plants... read more ) may result from inadequate intake, inadequate supplementation, or malabsorption. Malodorous flatulence, diarrhea, or both may develop, particularly after malabsorptive procedures. Calcium and vitamin D absorption may be impaired, causing deficiencies and sometimes hypocalcemia Hypercalcemia Hypercalcemia is a total serum calcium concentration > 10.4 mg/dL (> 2.60 mmol/L) or ionized serum calcium > 5.2 mg/dL (> 1.30 mmol/L). Principal causes include hyperparathyroidism... read more and secondary hyperparathyroidism. With prolonged vomiting, thiamin deficiency Thiamin Deficiency Thiamin deficiency (causing beriberi) is most common among people subsisting on white rice or highly refined carbohydrates in countries with high rates of food insecurity and among people with... read more may occur.

Patients may have symptoms of reflux, especially after sleeve gastrectomy. During rapid weight loss, cholelithiasis Cholelithiasis Cholelithiasis is the presence of one or more calculi (gallstones) in the gallbladder. Gallstones tend to be asymptomatic. The most common symptom is biliary colic; gallstones do not cause dyspepsia... read more (often symptomatic), gout Gout Gout is a disorder caused by hyperuricemia (serum urate > 6.8 mg/dL [> 0.4 mmol/L]) that results in the precipitation of monosodium urate crystals in and around joints, most often causing recurrent... read more , and nephrolithiasis Urinary Calculi Urinary calculi are solid particles in the urinary system. They may cause pain, nausea, vomiting, hematuria, and, possibly, chills and fever due to secondary infection. Diagnosis is based on... read more may develop. Concurrent cholecystectomy is considered if patients have preoperative symptomatic biliary disease but is no longer performed prophylactically.

Incidence of psychologic disorders such as depression Depressive Disorders Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and often by decreased interest or pleasure in activities. Exact cause is unknown... read more is increased in patients having metabolic and bariatric surgery. A 2016 meta-analysis confirmed this increase in preoperative depression and reported a postoperative decrease in the prevalence and severity of depression (1 Risks references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ). In a large review of retrospective and prospective studies, self-harm and suicide were higher in patients after metabolic and bariatric surgery than in control subjects; various presurgical and postsurgical factors may be involved (2 Risks references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ). Incidence of alcohol use disorder Alcohol Use Disorder and Rehabilitation Alcohol use disorder involves a pattern of alcohol use that typically includes craving and manifestations of tolerance and/or withdrawal along with adverse psychosocial consequences. Alcoholism... read more also appears to be increased after bariatric surgery (3 Risks references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Eating habits may be disordered. Adjusting to new eating habits can be difficult.

In hospitals accredited by the American Society of Bariatric Surgery as centers of excellence (COE), in-hospital mortality was 0.08% (1 Prognosis references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ). However, some data indicate that lower rates of serious complications are predicted more accurately by the number of procedures done in the hospital and by the surgeon than by COE status. Risk of death associated with bariatric surgery is about 0.1%; overall risk of serious complications is about 4%. For most patients, the risk of obesity and its complications outweigh the immediate risk of surgery (2 Prognosis references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Factors that predict higher risk of mortality include a history of deep venous thrombosis Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more or pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism (PE) is the occlusion of pulmonary arteries by thrombi that originate elsewhere, typically in the large veins of the legs or pelvis. Risk factors for pulmonary embolism are... read more , obstructive sleep apnea Obstructive Sleep Apnea (OSA) Obstructive sleep apnea (OSA) consists of multiple episodes of partial or complete closure of the upper airway that occur during sleep and lead to breathing cessation (defined as a period of... read more , and poor functional status. Other factors such as severe obesity Obesity Obesity is a chronic, multifactorial, relapsing disorder characterized by excess body weight and defined as a body mass index (BMI) of ≥ 30 kg/m2. Complications include cardiovascular disorders... read more (BMI > 50), older age, and male sex have also been associated with higher risk, but the evidence is inconsistent.

Average excess weight loss depends on the procedure.

For sleeve gastrectomy, loss of excess weight is

For Roux-en-Y gastric bypass, loss of excess weight is

Weight loss after RYGB is maintained for up to 10 years.

For BPD-DS and SADI-S, patients lose

In people who have severe obesity (≥ 50 kg/m2), weight loss is greater after BPD-DS than after RYGB (3 Prognosis references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ).

Comorbidities that tend to abate or resolve after metabolic and bariatric surgery include a large number of cardiovascular risk factors (eg, dyslipidemia Dyslipidemia Dyslipidemia is elevation of plasma cholesterol, triglycerides (TGs), or both, or a low high-density lipoprotein cholesterol (HDL-C) level that contributes to the development of atherosclerosis... read more , hypertension, diabetes), cardiovascular disorders, diabetes, obstructive sleep apnea Obstructive Sleep Apnea (OSA) Obstructive sleep apnea (OSA) consists of multiple episodes of partial or complete closure of the upper airway that occur during sleep and lead to breathing cessation (defined as a period of... read more , osteoarthritis, and depression Depressive Disorders Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and often by decreased interest or pleasure in activities. Exact cause is unknown... read more . Diabetes is particularly likely to remit (eg, with RYGB, up to 62% of patients at 6 years [ 4 Prognosis references Metabolic and bariatric surgery is the surgical alteration of the stomach, intestine, or both to cause weight loss in patients with obesity-related metabolic disorders and their sequellae. In... read more ]). All-cause mortality decreases by 25%, primarily because cardiovascular and cancer mortality is reduced.

Regular long-term follow-up after metabolic and bariatric surgery helps ensure adequate weight loss and prevent complications. After Roux-en-Y gastric bypass or sleeve gastrectomy, patients should be monitored every 4 to 12 weeks during the period of rapid weight loss (usually about the first 6 months after surgery), then every 6 to 12 months thereafter.

Weight and blood pressure are checked, and eating habits are reviewed. Blood tests (usually complete blood count; electrolyte, glucose, blood urea nitrogen, creatinine, albumin, and protein levels; and liver tests) are done at regular intervals. Glycosylated Hb (HbA1c) and fasting lipid levels should be monitored if they were abnormal before surgery. Depending on the type of procedure, vitamin and mineral levels, including calcium, vitamin D, vitamin B12, folate, iron, and thiamin (vitamin B1), may need to be monitored. Because secondary hyperparathyroidism is a risk, parathyroid hormone levels should also be monitored. Bone density should be measured after sleeve gastrectomy or Roux-en-Y gastric bypass.

Clinicians should check for any changes in response to antihypertensives, insulin, oral hypoglycemics, or lipid-lowering medications during the period of rapid weight loss after surgery.

Patients should also be regularly screened for depression Diagnosis Depressive disorders are characterized by sadness severe enough or persistent enough to interfere with function and often by decreased interest or pleasure in activities. Exact cause is unknown... read more and alcohol use Screening Alcohol use disorder involves a pattern of alcohol use that typically includes craving and manifestations of tolerance and/or withdrawal along with adverse psychosocial consequences. Alcoholism... read more , particularly if alcohol use was heavy preoperatively.

To minimize risk of hypoglycemia Hypoglycemia Hypoglycemia, or low plasma glucose level can result in sympathetic nervous system stimulation and central nervous system dysfunction. In patients with diabetes who take insulin or antihyperglycemic... read more (due to increased insulin sensitivity after bariatric surgery) in patients with diabetes, clinicians should adjust the dose of insulin and decrease the dose of oral hypoglycemics (particularly sulfonylureas) or stop them after Roux-en-Y gastric bypass or sleeve gastrectomy.