Bariatric surgery for management of obesity: Indications and preoperative preparation

INTRODUCTION — Obesity, defined as a body mass index (BMI) ≥30 kg/m², is a chronic illness identified in children, adolescents, and adults worldwide [1,2]. According to the World Health Organization, worldwide there are approximately 650 million adults with obesity and 42 million children with obesity under the age of five years [3]. In the United States, 35 percent of adults (roughly 100 million people) and 17 percent of children have obesity [4].

The surgical procedures performed to manage obesity are collectively referred to as metabolic or "bariatric" surgery (from the Greek words "baros," meaning "weight," and "iatrikos," meaning "medicine"). This topic will discuss the indications and contraindications for a bariatric surgical procedure as well as the optimal preoperative preparation in a multidisciplinary setting. A description of the types of bariatric procedures, as well as the complications and outcomes, is found in separate topics.

●(See "Bariatric procedures for the management of severe obesity: Descriptions".)

●(See "Bariatric operations: Late complications with subacute presentations".)

●(See "Outcomes of bariatric surgery".)

Screening, the general medical approach to the management of obesity, and clinical practice guidelines from the American College of Physicians for management of obesity in primary care settings are discussed elsewhere. (See "Obesity in adults: Prevalence, screening, and evaluation" and "Obesity in adults: Overview of management".)

BACKGROUND — There are several well-established health hazards linked to obesity, including type 2 diabetes mellitus, heart disease, stroke, cancers (eg, breast, colon, uterine), osteoarthritis, liver disease, obstructive sleep apnea, and depression (table 1). The risk of developing complications rises with increasing adiposity, while weight loss can reduce the risk or improve medical conditions, such as for hypertension and diabetes. (See "Overweight and obesity in adults: Health consequences" and "Obesity: Association with cardiovascular disease", section on 'Benefits of weight loss'.)

In addition to the impact on health, the economic costs of obesity are staggering [5-7]. The cost of treating obesity and its complications in the United States (US) is over 200 billion US dollars per year and over 20 percent of the US's entire health expenditure [6,8]. Additionally, obesity and its complications lead to other significant costs, such as missed days of work and decreased life expectancy [5]. Similar trends have been reported in other parts of the world [9,10].

Medical and behavioral approaches to weight loss may be ineffective for many individuals with obesity. The best method for obtaining and sustaining significant weight loss for such patients and treating comorbidities such as hypertension, hyperlipidemia, sleep apnea, and type 2 diabetes mellitus is obesity surgery. Patients who undergo bariatric surgery have lower long-term mortality rates compared with matched controls who did not have bariatric surgery [11]. (See "Outcomes of bariatric surgery".)

Hence, bariatric surgical procedures are increasingly common worldwide. The International Federation for the Surgery of Obesity and Metabolic Diseases estimates that there were about 394,431 bariatric procedures performed worldwide in 2018 [12]. Countries where >10,000 bariatric procedures were performed in 2014 include [13,14]:

●US and Canada (n = 256,000 in 2019 [15])

●Brazil (n = 65,000)

●France (n = 27,648)

●Mexico (n = 19,000)

●Australia and New Zealand (n = 12,000)

●United Kingdom (n = 10,000)

INDICATIONS — Indications for the surgical management of severe obesity were first outlined by the National Institutes of Health (NIH) Consensus Development Panel in 1991 [16]. In 2017, an international consensus conference, the second Diabetes Surgery Summit (DSS-II), called for expanding access to bariatric surgery to individuals of lower body mass index, different ethnic groups, and those with inadequate control of hyperglycemia [17]. These broader inclusion criteria have since been endorsed by 45 international medical and scientific organizations. In 2022, the American Society of Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) published updated indications for bariatric surgery [18]. Candidates for a bariatric surgical procedure include:

●Adults with a body mass index (BMI) ≥35 kg/m² regardless of the presence, absence, or severity of comorbidities. Bariatric surgery has been proven superior to diet, exercise, and other lifestyle interventions in attaining substantial and durable weight loss and improving obesity-related comorbid conditions in class II or greater obesity [19-29]. (See "Outcomes of bariatric surgery".)

●Adults with a BMI between 30.0 and 34.9 kg/m² and type 2 diabetes. Bariatric surgery is now considered to be a treatment option for diabetes in patients with class I obesity who do not achieve substantial or durable weight loss or comorbidity improvement with nonsurgical methods. Large retrospective and prospective studies that either included or exclusively enrolled patients with class I obesity have demonstrated superior and durable weight loss and diabetes control with bariatric surgery [17,30-48]. (See "Management of persistent hyperglycemia in type 2 diabetes mellitus", section on 'Bariatric (metabolic) surgery' and "Outcomes of bariatric surgery", section on 'Diabetes mellitus'.)

●Adults with a BMI between 30.0 and 34.9 kg/m² who cannot achieve substantial or sustainable weight loss or comorbidity improvement with nonsurgical weight loss methods. Ample data consistently demonstrate the weight loss and metabolic benefits of bariatric surgery in individuals with class I obesity [49]. The comorbid conditions that are often tied to obesity and can be improved by weight loss include:

•Type 2 diabetes [17,48].

•Obstructive sleep apnea (OSA).

•Hypertension.

•Hyperlipidemia.

•Obesity-hypoventilation syndrome (OHS).

•Pickwickian syndrome (combination of OSA and OHS).

•Nonalcoholic fatty liver disease (NAFLD).

•Nonalcoholic steatohepatitis (NASH).

•Pseudotumor cerebri.

•Gastroesophageal reflux disease.

•Asthma.

•Venous stasis disease.

•Severe urinary incontinence.

•Debilitating arthritis.

•Impaired quality of life.

•Disqualification from other surgeries due to obesity (ie, surgeries for osteoarthritic disease, ventral hernias, or stress incontinence).

Consideration should be given for race. There is growing evidence that the prevalence of diabetes and cardiovascular disease is higher at a lower BMI in the Asian than in the non-Asian population due to a higher prevalence of truncal obesity (ie, visceral fat), which is felt to be more hazardous than peripherally located fat [50]. Thus, BMI criteria can be lowered by 2.5 kg/m² per class, and those with BMI ≥27.5 kg/m² can be offered bariatric surgery rather than 30 kg/m² as above.

It should be noted that many bariatric surgery programs encourage (or require) patients to participate in lifestyle changes prior to surgery to demonstrate their commitment, but any resultant weight loss could decrease the patient's BMI to the extent that the patient no longer meets the criteria at the time the surgery is finally scheduled, even though they met criteria upon entry into the bariatric surgery program. The overwhelming majority of bariatric surgeons feel that such a reduction in BMI should not prevent the patient from having surgery and will typically use the initial entry BMI.

The ASMBS recognizes obesity as a chronic disease, and any weight lost in preparation for surgery is not likely to be substantial enough to treat comorbidities, and also not likely to be sustained [51]. As such, this preoperative weight loss should not preclude surgery [52]. (See 'Preoperative weight loss' below.)

The policy of the individual surgeon should be discussed with the patient relative to the accepted indications for bariatric surgery. Not proceeding with surgery is an option if the patient feels they may be able to continue to lose weight and sustain their weight loss without surgery. Insurance coverage is very variable by carrier and policy, and substantial preoperative weight loss can adversely change insurance coverage benefits for weight loss surgery.

CONTRAINDICATIONS — Bariatric procedures should not be performed for glycemic or lipid control or for cardiovascular risk reduction independent of the body mass index (BMI) parameters [53]. (See 'Indications' above.)

Other medical or psychiatric conditions that preclude a bariatric surgical procedure include:

●Untreated major depression or psychosis

●Uncontrolled and untreated eating disorders (eg, bulimia [53])

●Current drug and alcohol abuse

●Severe cardiac disease with prohibitive anesthetic risks

●Severe coagulopathy

●Inability to comply with nutritional requirements including lifelong vitamin replacement

There is no upper patient age limit to bariatric surgery. Instead, fragility is a better predictor of outcome than age alone [54,55]. Bariatric surgery for patients younger than 18 years is becoming more common and is endorsed for use by the American Academy of Pediatrics for patients with severe obesity under the recommendation that only high-quality programs that provide both pediatric and transition to adult care be allowed to perform it in this population [56,57]. (See "Surgical management of severe obesity in adolescents".)

Additionally, bariatric surgery is an effective treatment for clinically severe obesity in patients who need other specialty surgery, such as joint arthroplasty, abdominal wall hernia repair, or organ transplantation [18].

PREOPERATIVE ASSESSMENT — Bariatric surgery should be performed in conjunction with a comprehensive preoperative assessment and a follow-up plan consisting of medical, nutritional, and behavioral programs.

A multidisciplinary team that includes a primary care provider, nutritionist, medical bariatric specialist, psychologist/psychiatrist, nurse specialist, and skilled surgeon offers well-rounded assessments and support for those considering a bariatric surgical procedure. The advantage of the team approach is assistance provided to the patient that facilitates the long-term lifestyle changes conducive to long-term maintenance of weight loss.

Psychosocial assessment — All patients seeking bariatric surgery should be assessed by a qualified behavioral health clinician for psychosocial functioning, substance abuse, or maladaptive eating behaviors [58]. Any psychopathology, substance abuse, or eating disorder uncovered should receive adequate referral and treatment. All patients should also be educated about new psychosocial problems that could emerge after bariatric surgery.

Individuals with obesity, especially those seeking bariatric surgery, have a higher prevalence of mental health impairments than the general population [59]. The goal of presurgical psychologic testing is to identify any previously undiagnosed psychiatric disorders and determine if an operative candidate is able and willing to make the necessary lifestyle changes required for sustainable weight loss. Any significant psychiatric disorders (eg, bipolar disorder, major depression, antisocial personality disorder) can then be treated preoperatively to minimize challenges to weight loss initiatives and reduce risk for postoperative psychiatric complications [60].

Untreated major depression or psychosis, uncontrolled and untreated eating disorders (eg, bulimia), and active drug or alcohol abuse are contraindications to bariatric surgery. (See 'Contraindications' above.)

After bariatric surgery, new psychosocial issues may arise ranging from problems with interpersonal relationships, body image, or day-to-day functioning to severe, even life-threatening psychopathologies (eg, self-harm, suicide). (See "Outcomes of bariatric surgery", section on 'Psychosocial impact'.)

Nutritional assessment — All patients seeking bariatric surgery should be evaluated by a registered dietitian for the following [61]:

●Weight history and eating behaviors – Patterns of previous weight loss and regain provide information about eating habits and lifestyle that may be relevant to the management of the short-term and long-term postoperative course. The lack of previous weight loss attempts should not preclude consideration for bariatric surgery [62-64]. Eating and dietary style queries should include for binge eating, grazing, overeating, nighttime eating, and stress-related eating patterns, which may identify maladaptive eating styles.

●Medication review – Medications that can be potentially associated with weight gain or increased appetite include antihypertensives, diabetes medications, hormone therapies, antiseizure medications, antidepressants, mood stabilizers, antipsychotics, migraine medications, and anti-inflammatory agents [58]. If possible, a substitution should be made in consultation with the prescriber.

●Body composition and energy requirement analysis – If available, a baseline measurement of the patient's body composition and energy requirement should be made [65]. Repeat measurements after surgery will help prescribe caloric requirements and ensure long-term weight loss.

●Micronutrient deficiency analysis – A nutrition-focused physical examination and specific bariatric micronutrient (thiamin; vitamins B12, A, E, D, and K; folate; iron studies; ferritin; and calcium) assessment should be performed. Most individuals seeking bariatric surgery have at least one micronutrient deficiency [66]. Early diagnosis permits replacement therapy and improved monitoring postoperatively. (See "Bariatric surgery: Postoperative nutritional management", section on 'Presurgical screening'.)

In addition, with the dietician's help, all patients should make nutritional plans for before, around the time of, and after bariatric surgery. Nutritional education should also provide information on how to read the nutritional content of foods, select appropriate portion sizes, find snack and beverage alternatives, prepare foods, and shop for one's loved ones (if applicable). Many programs will also provide meal preparation classes for their patients.

Medical assessment — Individuals seeking bariatric surgery should be evaluated by a medical bariatric specialist, their primary care provider, and additional specialists (eg, cardiologist, pulmonologist) to ensure that they can tolerate and are optimized for the proposed surgery.

History and physical examination — A complete history and physical examination is performed to assess for comorbid illnesses, such as hypertension, diabetes, obstructive sleep apnea (OSA), malnutrition, restrictive lung disease, and the individual's appropriateness as a surgical candidate. Many patients have undiagnosed ailments related to their obesity.

Laboratory studies

●For patients with renal dysfunction due to longstanding hypertension or diabetes, we obtain serum chemistry tests that include blood urea nitrogen and creatinine.

●For patients suspected to have nonalcoholic fatty liver disease (NAFLD) on the basis of hepatomegaly on the physical examination, liver function tests are obtained [67]. The need for liver biopsy should be guided by preoperative clinical scores, liver stiffness measurement, and any signs of portal hypertension/chronic liver disease [68]. (See "Epidemiology, clinical features, and diagnosis of nonalcoholic fatty liver disease in adults".)

●Baseline glycated hemoglobin (A1C) and fasting glucose levels should be obtained in all patients seeking bariatric surgery [58,69]. Patients with known or newly diagnosed type 2 diabetes or prediabetes should be treated before surgery, and early postoperative hyperglycemia should be avoided. In bariatric surgery, adverse outcomes have closer association with early postoperative glycemic control than with preoperative A1C value [70,71]. Thus, bariatric surgery should not be delayed or withheld for a high preoperative high A1C value.

●A fasting lipid panel should be obtained in all patients seeking bariatric surgery. Those diagnosed with dyslipidemia should be treated [72].

●Testing for gout and subsequent treatment of gout in all patients seeking bariatric surgery are recommended. Given the high likelihood of gouty attacks postoperatively, prophylaxis may be warranted in those who have a history of gout. (See "Nonpharmacologic strategies for the prevention and treatment of gout".)

●We test for hypothyroidism in patients who have symptoms. We do not obtain thyroid-stimulating hormone (TSH) in asymptomatic patients, as TSH level can be elevated in euthyroid patients with obesity. (See "Clinical manifestations of hypothyroidism".)

Further assessments — Based upon the medical history, physical examination, and laboratory tests, the preoperative medical assessment may also involve other specialists in the following areas:

●Obstructive sleep apnea – The prevalence of OSA in individuals with obesity ranges from 35 to 94 percent, with most studies reporting a rate >60 percent [73]. Thus, screening for OSA with one of the questionnaire-based methods such as STOP-Bang (table 2) is recommended for all patients seeking bariatric surgery. Confirmatory tests, such as polysomnography (ie, sleep study) or home polygraphy, should be offered to those who are at high risk of having OSA based upon the initial screen. Patients with diagnosed severe OSA and/or obesity-hypoventilation syndrome should be referred to a pulmonologist. Those with moderate-to-severe OSA may also benefit from positive continuous airway pressure (CPAP) therapy. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Screening with a questionnaire' and "Clinical presentation and diagnosis of obstructive sleep apnea in adults".)

●Cardiac assessment – There is no bariatric-surgery-specific protocol for preoperative cardiac assessment. Thus, we use the standard approach [58]. (See "Evaluation of cardiac risk prior to noncardiac surgery".)

We screen all patients with a validated cardiac risk calculator (eg, the Revised Cardiac Risk Index), determine their functional capacity, and perform an electrocardiogram. We then refer low-risk patients to their primary care provider for cardiac clearance and high-risk patients and those with a moderate-to-severe preexisting cardiovascular disease (eg, recent myocardial infarction, unstable angina, uncompensated heart failure, high-grade arrhythmia, or hemodynamically significant valvular heart disease) to a cardiologist for further testing/evaluation.

It should be noted that bariatric surgery has strong cardiovascular benefits and a very low risk profile and therefore should be considered even in patients with significant cardiac disease and/or risk [74]. (See "Outcomes of bariatric surgery", section on 'Cardiovascular risk'.)

●Gastrointestinal assessment – Depending on the bariatric procedure planned and symptoms (eg, reflux, dysphagia), some patients may benefit from additional assessment of the upper digestive system, including possible upper gastrointestinal series, upper endoscopy, esophageal pH study, or manometry. This is discussed in topics on individual bariatric procedures. (See "Laparoscopic sleeve gastrectomy", section on 'Preoperative workup' and "Laparoscopic Roux-en-Y gastric bypass", section on 'Preoperative workup'.)

●Cancer screening – Obesity increases the prevalence of a number of malignancies. As such, patients seeking bariatric surgery should be encouraged to undergo age-appropriate cancer screening such as colonoscopy and mammography [75].

Anesthetic risk assessment — Obesity leads to respiratory and cardiovascular changes that impact the delivery of general anesthesia along with perioperative analgesia. The physiologic and anatomic changes associated with obesity and the management of anesthetics and analgesics are reviewed separately. (See "Anesthesia for the patient with obesity" and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea".)

PREOPERATIVE INTERVENTIONS — The following interventions are strongly encouraged in all individuals seeking bariatric surgery. Some have been shown to improve outcomes after bariatric surgery; for the others, the benefit is inferred from similar nonbariatric surgeries.

Smoking cessation — Tobacco smoking within one year prior of bariatric surgery is known to increase 30 day mortality and major postoperative complications [76,77]. Smoking cessation programs initiated four to eight weeks before general and orthopedic surgery have reduced complication rates [78]. Thus, patients seeking bariatric surgery who smoke tobacco or marijuana should be encouraged to stop smoking at least six weeks before bariatric surgery.

Patients should be referred to their primary care provider or a dedicated smoking cessation program. Nicotine replacement therapy is safe and efficacious for use in preoperative smoking cessation programs, while other agents are less well studied.

In a prospective cohort study of 1770 patients who underwent Roux-en-Y gastric bypass, 45 percent reported a history of smoking [79]. Modeled prevalence of current smoking decreased in the year before surgery from 13.7 to 2.2 percent at surgery but increased to 9.6 percent one year post-surgery and continued to increase to 14.0 percent seven years post-surgery. In another study, 65 percent of recent smokers resumed smoking after bariatric surgery, with about half experiencing a marginal ulcer after Roux-en-Y gastric bypass [80].

Though it is not clear what impact smoking relapse has after sleeve gastrectomy, it is recommended that tobacco cessation therapy be continued after all bariatric surgery. (See "Pharmacotherapy for smoking cessation in adults".)

Alcohol cessation — In general, it is recommended that all alcohol use should be stopped before bariatric surgery, but the exact timing for this is unknown. In patients with a known alcohol abuse diagnosis, alcohol drinking should be stopped for at least one year before surgery [81]. Alcohol use or a history of alcohol abuse, though, are not contraindications to bariatric surgery [82]. Certainly, patients with known liver disease, whether or not it is related to alcohol, have a higher risk of postoperative complications [83]. Postoperatively there is a significant incidence of alcohol abuse after bariatric surgery, and thus each patient must be informed about this and monitored for this [84]. (See "Outcomes of bariatric surgery", section on 'Alcohol and other substance abuses'.)

Estrogen cessation — Estrogen-containing oral contraceptives and hormone-replacement therapy increase venous thromboembolic (VTE) risk, which compounds the VTE risk of obesity [85,86]. With regards to bariatric surgery, the information is less robust, but it is generally recommended to avoid estrogen-containing forms of contraception prior and post-surgery [87].

●Women should stop taking estrogen-containing oral contraceptives for one month before bariatric surgery [88]. They should consult with their gynecologist to seek safe alternatives such as progestin-only oral contraceptives or an intrauterine device. (See "Combined estrogen-progestin contraception: Side effects and health concerns", section on 'Venous thromboembolism'.)

Furthermore, they should be told that pregnancy is discouraged within the first 18 to 24 months after surgery. Although patients are not required to be on birth control during that period of time, they should be given the opportunity to discuss their options. Estrogen-containing contraceptives should be avoided in the perioperative period for at least one month due to the continued risk of VTE. Women interested in contraception should also discuss the bioavailability of their birth control pill with their gynecologist; patients undergoing a malabsorptive procedure may not adequately absorb certain birth control pills to prevent pregnancy. (See "Fertility and pregnancy after bariatric surgery", section on 'Contraception'.)

●Women should stop taking hormone replacement therapy for three weeks before bariatric surgery [88]. (See "Menopausal hormone therapy: Benefits and risks", section on 'Venous thromboembolism'.)

For all patients with hypercoagulable states or a history of a VTE event, consultation with hematology/oncology should be obtained to determine the type and duration of perioperative thromboprophylaxis. (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients", section on 'Selecting thromboprophylaxis'.)

Preoperative weight loss — There is evidence that a low- (800 to 1200 kcal) or very-low- (400 to 800 kcal) calorie diet for 2 to 12 weeks may induce sufficient weight loss to improve the technical ease of bariatric surgery by reducing the volume of the liver (by 15 to 30 percent) and overall adiposity [58].

However, inability to adhere to such a strict diet or lose weight should not preclude bariatric surgery, and such dieting should not be confused with insurance-mandated preoperative diets. (See 'Indications' above.)

Prehabilitation — Prehabilitation programs are 4 to 12 weeks of supervised physical exercise, aggressive diabetes control, alcohol and tobacco cessation, and pulmonary interventions typically given as a part of Enhanced Recovery After Surgery (ERAS) programs. While there is general success with the use of ERAS protocols, the extent to which prehabilitation helps is unknown. With major abdominal surgery, prehabilitation has been shown to improve patient outcomes such as reduced overall and pulmonary complications and shorter length of stay; data are more limited in bariatric surgery [89]. It is not known whether prehabilitation is required or can benefit laparoscopic bariatric surgery or a subset of individuals such as those with class 3 obesity. (See "Overview of prehabilitation for surgical patients".)

PREOPERATIVE COUNSELING — Bariatric surgical candidates should have the intellectual resources to understand the type of procedure to be performed, the risks of the procedure, and the behavioral changes that are key to effective weight loss. Deficits can be addressed, such as training the patient to develop coping skills, counseling to eliminate maladaptive behavior, and taking the time to educate the patient not only on the risks and benefits of the surgery but also the risks of obesity [61].

Psychosocial, emotional, and lifestyle expectations should be assessed to determine if they are realistic and if the patient is committed to actively and permanently following postoperative guidelines for improved health. Many patients with obesity may have preconceived ideas about the benefits of bariatric operations and lack a realistic expectation of the lifestyle changes that are mandatory to achieve weight loss goals. Preoperative counseling should reinforce goals and the means to achieve them.

The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) bariatric surgical risk/benefit calculator estimates the chance of an unfavorable outcome (such as a complication or death), the chance of remission of weight-related comorbidities, and the patient's body mass index (BMI), weight change, and percent total weight change after surgery. These outcomes are calculated using the patient's preoperative information as well as data from a large number of other patients who had a similar bariatric surgical procedure.

Overall, the 30 day risk models were accurate and well calibrated, with acceptable discrimination [90]. The MBSAQIP bariatric surgical risk/benefit calculator is publicly available, with the intent to be integrated into health care practice to guide bariatric surgical decision making and care planning and enhance communication between patients and their surgical care team.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Bariatric surgery".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Weight loss surgery (The Basics)")

●Beyond the Basics topics (see "Patient education: Losing weight (Beyond the Basics)" and "Patient education: Weight loss surgery and procedures (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Background – Obesity is a worldwide chronic condition that affects children, adolescents, and adults with huge health and economic impacts. As medical and behavioral approaches to weight loss may be ineffective for many individuals with obesity, bariatric surgical procedures are increasingly common worldwide. (See 'Introduction' above and 'Background' above.)

●Indications – Appropriate candidates for bariatric surgery include (see 'Indications' above):

•Adults with a body mass index (BMI) ≥35 kg/m² regardless of the presence, absence, or severity of comorbidities.

•Adults with a BMI between 30.0 and 34.9 kg/m² and type 2 diabetes.

•Adults with a BMI between 30.0 and 34.9 kg/m² who cannot achieve substantial or sustainable weight loss or comorbidity improvement with nonsurgical weight loss methods.

For Asian patients, the BMI criteria can be lowered by 2.5 kg/m² per class, related to a higher prevalence of truncal obesity (ie, visceral fat).

●Contraindications – Bariatric procedures are not performed for (see 'Contraindications' above):

•Glycemic or lipid control or cardiovascular risk reduction independent of the BMI parameters.

•Untreated or uncontrolled psychosocial disorders (eg, major depression, psychosis, bulimia, substance abuse).

•Inability to tolerate surgery (eg, severe cardiopulmonary disease, coagulopathy).

•Inability to comply with postoperative nutritional requirements (eg, vitamin supplementation).

●Preoperative assessments – Patients seeking bariatric surgery should be assessed by (see 'Preoperative assessment' above):

•A qualified behavioral health clinician for psychosocial functioning, substance abuse, or maladaptive eating behaviors.

•A registered dietitian for weight history and eating behavior, medication review, body composition and energy expenditure, and micronutrient deficiency.

•The bariatrician, primary care provider, or other specialists for obstructive sleep apnea (OSA), diabetes, heart disease, dyslipidemia, gout, and hypothyroidism, among other comorbid conditions.

●Preoperative interventions – Patients seeking bariatric surgery should be encouraged to (see 'Preoperative interventions' above):

•Stop smoking tobacco or marijuana at least six weeks before surgery.

•Avoid alcohol use for at least one year if there is a history of alcohol abuse. Stop alcohol use for at least one month prior to surgery, and counsel patients on the risk of developing alcohol abuse postoperatively.

•For all individuals seeking bariatric surgery, we suggest stopping estrogen-containing oral contraceptives one month or hormone replacement therapy three weeks before surgery to reduce the risk of venous thromboembolism (Grade 2C).

•Participate in a preoperative weight loss program with a low-caloric diet for 2 to 12 weeks before surgery.

•Participate in a physical exercise and pulmonary intervention (prehabilitation) program for 4 to 12 weeks before surgery.

●Preoperative counseling – Patients seeking bariatric surgery should be counselled to develop coping skills, eliminate maladaptive behavior, and understand the risks and benefits of the surgery. Online resources such as the Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) calculator may help patients set realistic expectations about the outcomes of their bariatric surgery. (See 'Preoperative counseling' above.)