Roughly 1.5 billion people live with obesity worldwide. This disease can exert appreciable adverse effects on virtually all aspects of a person’s life – physical, psychological, and socioeconomic. Empirically linked to several-year reductions in both quality-adjusted-life-years and lifespan, it confers increased risks for a host of life-altering and potentially life-threatening comorbidities including diabetes, cardiovascular disease, and at least 13 forms of cancer. Yet only a small minority of patients seeks formal treatment and few achieve meaningful, sustained weight loss or the amelioration of obesity-associated comorbidity. One major reason for this is woefully-inadequate knowledge among the public and amongst primary healthcare providers regarding various treatment options that have been proven effective.

In the latter part of 2020, a joint task force of the International Federation for the Surgery of Obesity and Metabolic Diseases (IFSO) and World Gastroenterology Organisation (WGO) convened to initiate the process of drafting comprehensive guidelines for the management of obesity. This multi-disciplinary task group consisted of nutritionists/dieticians, psychology/behavioural healthcare professionals, physician specialists in endocrinology and hepatology, and bariatric surgeons and endoscopists. Creating the guidelines involved four major steps: (a) thorough review of published obesity literature from a multi-disciplinary perspective; (b) a consensus survey of 94 international experts spanning all the healthcare fields listed above and guided by an international MD-PhD-level expert in consensus surveys; (c) drafting of guidelines for each field by experts in those fields; and (d) final collation, organization, editing, and approval of the guidelines by the task group. This paper summarizes the resultant guidelines.

Obesity is a chronic disease, characterized by both abnormal and/or excess body fat accumulation, that is multi-factorial in origin and influenced by various genetic, behavioural, and environmental factors(1) This state of hyper-lipidosis adversely affects someone’s health, increasing their risk for a range of co-morbid conditions and premature mortality, and reducing their overall quality of life(2). Life-altering and oftentimes life-threatening comorbid conditions that have been empirically linked to obesity include type 2 diabetes mellitus (T2DM)(3, 4, 5), cardiovascular disease(5, 6, 7, 8), sleep apnoea(9, 10), chronic kidney disease(11, 12), and at least 13 distinct forms of cancer that, amongst others, include breast, colorectal, hepatocellular, ovarian, and pancreatic malignancies and multiple myeloma(13, 14). More recently, obesity has been empirically documented to be an independent risk factor for adverse health outcomes, including death, in persons with coronavirus disease-19 (COVID-19)(15, 16, 17, 18). For all these reasons, obesity is now considered a leading cause of chronic disease, disability, morbidity, and both direct and indirect healthcare costs worldwide.

Tragically, prevalence rates for obesity are increasing globally and in all age groups, including children and adolescents(19, 20, 21, 22). This said, how quickly these rates have been increasing over the past decade has varied geographically. Consequently, geographical origins and ethnicity are considered important factors in the pathophysiology of obesity and its associated diseases, and interventions targeting obesity and its co-morbidities must take such links into consideration to optimize their effectiveness(23).

Much of the diminished general health and life quality that individuals living with obesity experience stems from this extensive array of co-morbid health conditions that influence virtually every organ system and both physical and psychological health. Besides T2DM, cardiovascular disease, sleep apnoea, renal disease and cancer, such conditions include metabolic syndrome(24, 25), liver disease(26, 27, 28), gallbladder disease(29, 30), pancreatitis(29, 30), venous thromboemboli(31), urinary stress incontinence(32, 33), idiopathic intracranial hypertension(34, 35), osteoarthritis(36), and psychiatric disorders like depression and anxiety(37, 38, 39, 40, 41). It is crucial that such conditions are recognized for several reasons that include (a) their potential for severe and even life-threatening consequences, and (b) how many of these conditions, including diabetes and cardiovascular disease, have been documented to improve or even abate altogether following successful metabolic and bariatric surgery (MBS) or bariatric endoscopy. On the other hand, certain other conditions, like the risk of certain cancers, may or may not decline after MBS.

Diagnosing, managing, and monitoring comorbid conditions are among numerous valid arguments for healthcare practitioners to adopt a multi-disciplinary team approach to managing patients with obesity. Another is that the management of obesity has changed dramatically in recent decades with the emergence of a broad array of procedural (e.g., surgical and endoscopic) therapies that have proven more effective than conservative therapy alone – with respect to achieving and maintaining weight loss, reducing comorbidities, and improving patients’ overall quality of life(42, 43, 44, 45). Yet another rationale for multi-disciplinary management is that the presence of obesity-associated physical and psychiatric conditions, their severity, and how well they are being controlled can all influence decisions both about whether surgical therapy is indicated and safe for a given patient, and which operative procedures to consider.

It was with this in mind that a multidisciplinary board of advisors – including members of both the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) and World Gastroenterology Organisation (WGO) – was created in the latter part of 2020 for the primary purpose of constructing and ultimately publishing consensus guidelines for the management of obesity and its associated co-morbid conditions. Drafting these guidelines relied on (a) a thorough literature review conducted by a multidisciplinary team – consisting of bariatric surgeons and endoscopists, internists specializing in either endocrinology or hepatology, nutritionists/dieticians, and psychology/behavioural healthcare professionals – all members having extensive experience in obesity management; (b) a three-stage, online consensus (Delphi) survey to identify areas of consensus and non-consensus in obesity management amongst 94 international experts spanning all the fields of expertise listed above and six continents; and (c) the drafting of guidelines, by the same multi-disciplinary team. A full copy of the guidelines and all Delphi survey results have been published on both the IFSO (https://www.ifso.com) and WGO (https://worldgastroenterology.org) websites. A paper summarizing the Delphi survey’s design and results has also been published elsewhere(23). This paper summarizes the main points of the consensus guidelines.

For obesity management to be successful, a multi-disciplinary approach to both its assessment and treatment is required(2, 46, 47, 48); and such a multidisciplinary approach should begin with a comprehensive evaluation of each patient’s physical health and fitness, psychological health, nutritional health, dietary practices, and personal beliefs, goals, and expectations.  Such is true whether patients are being considered for conservative therapy (e.g., diet, exercise, counselling, medication) alone or combined with either an endoscopic or surgical bariatric procedure. Through these evaluations, patients typically learn about and are determined to be either eligible or ineligible for bariatric surgery by designated medical, psychology/behavioural health, and nutrition specialists.  Since patients are expected to schedule and attend appointments at which they will be interviewed and examined and may undergo procedures to determine if they are healthy enough to withstand bariatric surgery(49), this evaluation period also may help to predict their likely compliance and success in their obesity management program.

A trained psychotherapist, preferably with considerable expertise managing patients with obesity, should play a major role in this initial assessment. Such a psychological evaluation has several purposes. Among them is identifying dysfunctional eating behaviours — like binge-eating disorder, emotional eating, and food addiction — that could undermine the effectiveness of any therapeutic approach(50). Though the concept of ‘food addiction’ remains unproven and controversial(51), since obesity manifests many of the same symptoms, it also is important to assess for behavioural factors that might place patients at elevated risk of developing problems associated with alcohol and/or other substances and/or behavioural abuse over the course of treatment, especially if a more invasive and permanently life-altering approach like MBS is being considered(52).

Patients with a severe psychiatric disorder, like schizophrenia or bipolar disorder, must have it identified. However, the presence of such a condition, in itself, is not an absolute contraindication to MBS. Rather, it is the severity of psychiatric symptoms and how well they are being controlled that predict bariatric surgery outcomes, in terms of both weight loss and mental health consequences(53). In other words, even patients with a major psychiatric diagnosis like schizophrenia can be considered for MBS, if their psychiatric symptoms are well controlled.

Early psychological evaluations also need to assess each individual’s perceptions of their obesity and how stigmatized they feel because of it. This is because weight bias, obesity stigma, and discrimination all are experienced by a sizeable percentage of persons with obesity(54, 55), even within general healthcare settings(56, 57). Even healthcare providers who provide obesity management often hold biased beliefs and attitudes about obesity and people with obesity(58). To combat this, every member of an obesity management team must treat obesity as the chronic disease it is now recognized to be, both to counter patient perceptions that it is merely the result of weak willpower, and to reinforce to patients the importance of regular, life-long follow-up and adherence to treatment. Such healthcare providers must be especially vigilant regarding their own potential weight bias and recognize that patients who perceive such bias might become averse to adhering to ongoing follow-up and the overall treatment plan. It is also important for healthcare professionals performing initial psychological assessments to help patients establish realistic goals for weight loss and other outcomes – like diabetes control – early on, lest failure to achieve unrealistic levels of weight loss leads to later discouragement and either reduced patient compliance with, or dropout from, the treatment plan.

Obesity management also requires a detailed nutritional assessment and prolonged nutritional follow-up, even if surgery is elected as the cornerstone of therapy. As with psychological assessments, there are several reasons for this. First, as adjunctive therapy, dietary measures enhance surgical outcomes. Second, potentially life-threatening nutritional deficiencies may occur in patients who elect either for or against MBS(59, 60, 61, 62). Several recent clinical practice and best practices guidelines have been published that encompass nutrition care in patients who either intend to undergo or already have undergone MBS, including recommendations for a pre-operative medical work up and having a registered dietitian (RD) perform a nutritional assessment and provide education and ongoing monitoring(49, 59, 63, 64, 65, 66). It also is well established that the care of any patient undergoing MBS must begin pre-operatively, and that this must include pre-operative screening for micronutrient deficiencies, if excellent patient outcomes are to be achieved(59, 63, 64, 66). Obesity management should, therefore, begin with a thorough assessment of every patient’s nutritional status and dietary practices and any nutritional deficits that are identified must be corrected prior to MBS.

Exercise is another essential component of therapy, even if MBS is undertaken, as it induces health benefits like weight loss, reduced blood pressure, improved physical function, enhanced lipid profile, lower fasting glucose levels, improved mental health, and better overall quality of life(67, 68, 69). Studies also have revealed a 16-30% reduction in all-cause mortality risk in moderately-active individuals, versus those who are sedentary, irrespective of a patient’s body mass index (BMI) and waist circumference. Consequently, like their psychological and nutritional status, patients’ current level of physical fitness, exercise interests, and capacity for different exercise regimes must be assessed early on.

As a general principle and, again, irrespective of whether surgery is selected or rejected, all aspects of non-surgical management must be tailored to each individual patient, as no one diet, behaviour, exercise program, or medication will be accepted by or effective in all patients, and none has been documented as first-line or superior to all others. Long-term and preferably life-long monitoring of all non-operative components of obesity management also is required to continuously assess the effects of treatment, identify treatment non-response and/or intolerance, and detect any adverse effects that might have arisen from the treatments chosen.

Associated diseases – including type 2 diabetes (T2DM), obstructive sleep apnoea (OSA), hypertension and dyslipidaemia – also must be identified, be evaluated for severity, and have appropriate treatment initiated pre-operatively. Since obesity is a common risk factor for 13 different types of cancer, the importance of cancer screening should be reinforced, in accordance with national guidelines(46, 47, 49, 70). In patients considering MBS, a pre-operative upper gastrointestinal (UGI) endoscopic evaluation also is recommended if either a history or symptoms suggestive of gastro-oesophageal reflux disease (GERD) or other upper gastrointestinal pathology is reported, or if patients are on chronic anti-acid therapy(71). In present times, a patient’s coronavirus disease (COVID-19) status also is considered crucial(23), given the findings of several studies that have identified obesity as a significant, independent determinant of COVID-19 severity(72, 73, 74, 75, 76). Two special patient populations that warrant further discussion are seniors and adolescents, as elaborated in the next section.

Several observational studies have demonstrated that the overall risk of bariatric surgery in seniors is low, in terms of mortality and other severe outcomes(77, 78). However, the literature is contradictory regarding whether that risk is increased relative to that observed in younger adults. For example, in one meta-analysis of nine studies encompassing 4391 individuals who underwent RYGB (366 and 4025 >60-years-old and ≤60-years-old, respectively), significant rate elevations were detected among seniors for both morbidity (odds ratio, OR=1.88, 95% CI [1.07, 3.30], p=0.03) and mortality (OR=4.38 [1.25, 15.31], p=0.02)(79). On the other hand, another meta-analysis uncovered comparable complication rates in patients older than 60 versus 60 or younger, independent of the type of procedure performed(80). Certain specific complications may be more common among seniors, including some nutritional deficiencies(81), rendering close, long-term follow-up a necessity.  And though data are scarce comparing the different bariatric procedures, in terms of both efficacy and safety, numerous studies have identified laparoscopic RYGB as a viable option in elderly patients(79, 82, 83, 84, 85). Interestingly, though total weight loss may be less in older versus younger patients, the reverse appears to be true for metabolic response and comorbidity amelioration rates(86).

According to statistics published by the World Health Organization (WHO), more than 340 million individuals 19-years-old or under are currently affected by either overweight or obesity, including 39 million children under the age of five(20). As in adults, obesity in childhood is empirically linked to several adverse physical and mental health outcomes, including T2DM, steatohepatitis, sleep apnoea, cardiovascular disease, and polycystic ovary syndrome(87, 88, 89), as well as to negative societal outcomes, like poor self-esteem, reduced academic performance, depression, and decreased quality of life(88, 89). In addition, most adolescents with obesity continue to live with obesity as adults(90), with severe obesity in youths a particular concern. Risks of severe obesity during adolescence include several-year reductions in both life expectancy and quality years of life(91). With respect to treatment, short-term studies have shown that the results of MBS in adolescents are like those achieved in adults, in terms of efficacy, major complications, readmission rates, and mortality(23). Durable weight loss and improvements in both obesity-related co-morbidities and quality of life are often achieved. Laparoscopic sleeve gastrectomy (LSG) is the procedure most commonly performed in adolescents, followed by RYGB, while biliopancreatic diversion [duodenal switch] and one-anastomosis gastric bypass (OAGB) are generally not recommended in this age group(92). Unfortunately, despite a sizeable body of published empirical evidence confirming MBS as the most effective therapy for severe obesity in adolescents, the number of MBS procedures performed in adolescents is lagging behind the rapidly-increasing prevalence of severe obesity worldwide in this age-group(92, 93, 94). Likely, insufficient physician and public knowledge and the dearth of published long-term results on MBS in adolescents remain barriers preventing the referral of these youths for MBS(95).

One alternative to bariatric surgery that may be considered in select patients is endoscopic metabolic and bariatric therapy (EMBT), which includes a range of procedural therapies that rely on one of three predominant mechanisms of action. These mechanisms are restriction (reducing gastric capacity), biliopancreatic diversion (sectionally separating duodenal and upper jejunal mucosa and preventing the exposure of food to digestive juices), and the percutaneous aspiration of already-ingested gastric contents(96, 97). Forms of EMBT also can be categorized as either gastric or small intestinal(96, 97). Currently, only EBMTs that restrict gastric capacity – like various models of intragastric balloon (IGB) and endoscopic sleeve gastroplasty (ESG) – are being used in routine clinical practice. The current indication spectrum for EBMTs is a BMI ranging from 30kg/m² to just under 40kg/m²; or a BMI > 27kg/m² in patients with one or more concomitant, obesity-associated comorbidities.

In general, EMBTs are considered as safe, if not safer than MBS, though long-term data remain scarce. Advantages that EMBTs have over MBS are that most can be both repeated and reversed easily. Many EMBTs are, by their very nature (e.g., intra-gastric balloons), transient. Reported weight loss with EMBT generally ranges from ten to roughly twenty percent of total body weight. As such, they generally are recommended for use only in patients with less severe (class I or II) obesity or as bridge therapy in patients with more severe obesity awaiting MBS(23). More recently, the FDA has approved endoscopic sleeve gastroplasty (ESG) for patients with a BMI from 30-50mg/kg².  Long-term data up to five years reveal weight loss averaging 15% of total body weight (109). Further details regarding currently-practiced EMBT procedures are depicted and summarized in Table 1.

Of the various EMBTs available, by far the most supportive evidence has been published for intragastric balloons (IGB), with both randomized clinical trials and meta-analyses demonstrating statistically-significant weight loss and relatively-low rates of serious adverse events(98, 99, 100, 101, 102, 103). The most commonly-reported side effect and rationale for treatment discontinuation is nausea, with fluid-filled balloons tending to be slightly less well tolerated in this respect(104). On the other hand, in one meta-analysis comparing fluid-filled and gas-filled IGBs, fluid-filled balloons were linked to statistically greater and more consistent weight loss than gas-filled balloons(99). Several IGBs have already been approved by the US Food and Drug Administration (FDA) and received a CE (Conformitè Europëenne) mark.

Endoscopic sleeve gastroplasty (ESG) – which involves endoscopic placement of full-thickness running sutures along the greater curvature of the stomach – is another approach employed to reduce stomach volume endoscopically. One system – called the OverStitch^TM Endoscopic Suturing System (Apollo Endosurgery, Austin, TX) – has achieved both FDA and CE mark approval. In several meta-analyses comparing ESG against the more-invasive laparoscopic sleeve gastrectomy (LSG), findings generally indicate less weight loss but a tendency (albeit, not statistically significant) towards fewer adverse events with the former(105, 106, 107, 108). This said, meta-analysis authors have consistently recommended restricting the use of ESG to patients with mild to moderate (class I or II) obesity(105, 106, 107, 108, 109).

Far less supportive evidence exists for gastric delay and gastric aspiration procedures and their use remains limited, though specific approaches to both procedures have received FDA approval (Table 1). To date, neither FDA nor CE mark approval has been afforded to any small bowel bypass procedure.

Despite the emergence of EMBT, over the past few decades, a growing body of evidence has established MBS as the most effective treatment for obesity, with respect to reducing weight, improving numerous comorbid conditions that have been empirically linked to BMI, enhancing overall patient quality of life, and decreasing patient mortality(110). Among the various surgical approaches that are currently in use, sleeve gastrectomy (SG) and RYGB are currently the most commonly performed worldwide, in that order, though newer procedures, like one-anastomosis gastric bypass (OAGB)(111), show promise. Which procedure is employed should largely be decided on a patient-by-patient basis, that decision influenced by various patient characteristics – for example, evidence favours utilizing RYGB over SG in patients with GERD(112, 113, 114, 115) – as well as by the operating surgeon’s level of experience with each surgical approach. Regardless of which operation is chosen, patients must be thoroughly assessed by a multi-disciplinary team pre-operatively to determine their suitability for surgery and identify any issues that may require addressing.

As stated previously, pre-operative patient preparation for MBS involves ensuring that each patient has realistic goals and expectations pertaining to the benefits and potential problems that might arise from surgery, and that all psychosocial and behavioural barriers to adherence are addressed. Patients also must be alerted to any nutritional deficiencies and have such deficiencies corrected pre-operatively. Cessation of tobacco, alcohol and drugs is mandatory and should be maintained lifelong(23). Patients also should be assessed for and instructed in an exercise program that they can realistically resume post-operatively. In addition, during a life-threatening pandemic like COVID-19, suitable precautions must be taken to protect patients with obesity awaiting and undergoing MBS, because they are particularly vulnerable to severe COVID symptoms and mortality(72, 73, 74, 75, 76).

For MBS to be successful enhancing patient health appreciably and long-term, both patients and their healthcare providers need to make a life-long commitment to ongoing treatment and monitoring. This includes patients being monitored closely throughout the peri-operative period for peri-operative complications; then followed, essentially for the remainder of their life, preferably by the multi-disciplinary obesity-management team thus far involved in their assessment and management. This is because MBS alters so many facets of their life and physiology, potentially impacting them physically, psychologically, and socially. Some of these changes (e.g., weight loss, enhanced diabetes control) are desirable; whilst others (e.g., food intolerances, gastrointestinal discomfort, loose skin) are not. After MBS, for example, patients have an increased risk of developing such conditions as gallstones(116, 117, 118, 119), gout(120, 121, 122, 123), and nephrolithiasis(124, 125, 126, 127). Nutritional deficits also may develop, some of them potentially catastrophic, including but not limited to central and peripheral nervous system disorders(128, 129), severe protein malnutrition(62, 130), osteoporosis and osteomalacia secondary to both rapid weight loss and vitamin D deficiency(131, 132, 133, 134), iron-deficiency anaemia(135, 136), and immunocompromise(137). Such deficiencies have been documented to occur in as many 87% and 70% of patients undergoing RYGB and SG, respectively(138, 139). Consequently, besides monitoring, post-operative follow-up needs to include ensuring that patients adhere to nutritional guidelines and to taking vitamin and mineral supplements, as prescribed. Lifelong abstinence from tobacco, alcohol, and all recreational drugs also must be emphasized.

Ongoing changes may need to be made to patients’ medications and other treatments, as well, for a variety of reasons that include (a) either improvement or complete resolution of certain obesity-associated comorbidities – like reduced or eliminated insulin requirements for T2DM, and changes in night-time CPAP settings for obstructive sleep apnoea – and (b) anatomical changes induced by both MBS and EMBT that can appreciably alter the absorption of certain pharmaceuticals. Consequently, prior to MBS, medications that might be impacted by surgery need to be identified by the obesity management team. Then, after MBS and prior to patients’ discharge from the hospital, clear instructions on required post-operative medication changes and monitoring must be communicated both to patients themselves and to their primary physicians. Moreover, even if co-morbid conditions appear to resolve post-operatively, patients must continue to be monitored for them life-long, since disease recurrence may occur, sometimes independent of the patient’s weight loss trajectory.

Also as stated above, UGI endoscopic evaluation is recommended in patients with a history of reflux disease and in those undergoing gastric bypass surgery, both pre-operatively and every five years post-operatively. Since obesity is a risk factor for 13 different types of cancer, MBS patients also must continue to be screened for cancer post-operatively, in accordance with national guidelines. Nutritional intake, activity levels, adherence with multivitamin and mineral supplements, current weight, and both comorbidity assessments and blood tests should be done annually by the obesity management team.

Once a patient has undergone MBS, the centre where the surgery was conducted needs to, thus, relay a comprehensive post-operative health management plan to primary care providers(23), which must include which procedures, blood tests, and long-term vitamin supplements are required, any medication changes and/or monitoring that may be necessary, and when patients should be referred back to the MBS centre. Reasons for referral back to the MBS centre or to a local specialist include persistent GI symptoms, nutritional issues, pregnancy, a need for psychological support, appreciable weight regain, and other medical issues requiring bariatric care.

With respect to weight regain, it is crucial that patients and their primary health care providers understand that some degree of weight regain is typical(140), especially after two years post-operatively, and that even appreciable weight regain must never be considered treatment “failure”, as such a perception can exert detrimental effects on patients’ self-perception, motivation to continue treatment, compliance with further monitoring and treatment and, ultimately, their health outcomes(141, 142). Instead, just like patients who experience disease recurrence after cancer therapy, patients presenting with significant weight regain after MBS require an extensive evaluation, including anatomical studies (e.g., UGI endoscopy, UGI barium studies) and being assessed by the multidisciplinary team(143, 144).

Finally, weight regain is not the only clinical outcome that can warrant investigation after MBS. For example, patients presenting with GERD symptoms, with or without weight regain after MBS, also require an objective assessment to identify or rule out GERD, including pH studies with or without manometry(145).

Obesity has been called the world’s most extensive pandemic, and its prevalence, distribution, and costs continue to rise. To stem this rising tide of obesity and its numerous complications and costs, healthcare providers, insurers, and public officials must now work together, systematically, to increase public awareness about both the adverse health risks associated with obesity and the potential amelioration of such risks achieved when non-operative and operative therapy are combined. They also must work to eliminate the stigma associated with obesity, since such stigmatization can prevent individuals from seeking appropriate treatment and from adhering to such treatment once sought. This requires that everyone recognizes and treats obesity as the chronic disease it is now known to be, using a multidisciplinary team approach like that used for other chronic diseases, like diabetes, heart disease, and cancer. It is only through such concerted efforts that the steadily-worsening obesity pandemic can be reversed.

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Approximately 1.5 billion people worldwide currently live with obesity, and this number is steadily rising[2-4], even among children and adolescents[5]. Beyond its own implications for health and fitness, obesity increases the risk of numerous other potentially life-threatening complications, like type 2 diabetes mellitus (T2DM)[6], cardiovascular disease[7], and at least 13 types of cancer, including breast, colorectal, and ovarian, to name a few [8, 9]. Excess weight has also been linked to significantly-decreased quality of life[2], significantly-increased risk of early mortality, decreased life expectancy[10], and increased cancer-related mortality[11].  These risks even extend to childhood obesity[12].

Managing obesity is difficult, with “eating less and exercising more” rarely attaining long-term outcome success. Consequently,  and because of the numerous obesity-associated comorbidities, obesity has been termed “a chronic relapsing progressive disease”[13]. While dietary changes, other lifestyle changes like exercise, and counselling remain the first line of treatment, relatively-recent advances in obesity management have included pharmacological, endoscopic and surgical interventions.  Bariatric surgery remains significantly more effective than dietary and lifestyle changes alone, in terms of inducing weight loss, reducing comorbidities, and improving quality of life[14-17].

Several operative interventions currently exist.  The choice of which procedure is chosen and when to offer surgery will often vary between practices and regions[18]. Bariatric procedures also carry their own risks, including a low, but non-negligible (0.15-0.35%) risk of intra-operative mortality[19, 20].  Additional complications of bariatric surgery include potentially-fatal nutritional difficiencies[21-24]; post-operative bleeding, intestinal obstructions, severe gastroesophageal reflux, and various gastrointestinal syndromes[19].  Patients undergoing bariatric surgery may also be prone to developing new post-operative addictive behaviours such as substance abuse[25]. Consequently, bariatric surgery procedures should not be used to replace, but rather to supplement other, non-operative approaches to obesity management, including dietary and lifestyle changes. It is also important to identify and treat psychopathology, utilizing psychosocial counselling, and pharmacotherapy[25]. However, like the choice of operative procedures, considerable variability exists in how and to what extent such services are co-administered[26]. Variability also exists in which patients are considered eligible and safe for endoscopic and bariatric procedures[27]; how to define treatment success and failure[16, 28]; how much weight regain should be considered acceptable[29]; and which metric to utilize for measuring weight regain (e.g., excess vs. total weight lost)[30].

It was such variability and uncertainty in so many obesity management practices that led the World Gastroenterology Organisation (WGO) and International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO) to join forces in late 2020 to take steps towards drafting international guidelines on the assessment, treatment, and long-term monitoring of obesity.  This included undertaking a survey of international, interdisciplinary experts in obesity management to identify areas of consensus and non-consensus spanning a range of topics, the results of which could then be used to assist in the drafting of joint IFSO:WGO obesity management guidelines. This paper reports the results of the resultant multiple-round survey of 94 inter-disciplinary obesity-management experts spanning six continents.

A decision was made to conduct a two-round, on-line, modified Delphi survey, following published Delphi survey guidelines[31].  The Delphi approach was adopted because of its exponentially-increasing utilization in health science and other fields to identify areas of expert consensus and non-consensus. Among the major benefits of Delphi surveys is their unanimous voting, which reduces the risk of conformity/acquiescence bias typically ascribed to in-person consensus meetings[31].

Survey development began by asking each steering committee member to generate a list of issues/questions of major interest, particularly within their own discipline. To be considered for survey inclusion, the issue could not already be considered a firmly-established, universal standard of care based upon published empirical evidence, yet still be considered of appreciable importance to the management of overweight or obesity. Such issues could pertain to virtually any aspect of obesity management, from epidemiology and public perceptions to treatment and follow-up.

The lists that were created were sent to the Delphi survey expert for editing, consolidation into a single survey, and reformatting to ensure comprehensibility and consistency of presentation. Survey development included several steps to reduce the risk of bias potentially induced by the survey itself, including (a) primarily using non-judgmental statements (e.g., neither favouring nor opposing a particular concept/belief/approach); (b) balancing the remaining number of favourable and unfavourable statements; (c) altering the order of response options to minimize the risk of order bias (e.g., listing the most favourable response option anywhere from first to last); and (d) conducting a pilot survey of 10 experts to identify concerns and any language, factual, or conceptual errors.

Prior to the pilot survey, the survey’s first full draft was sent to all steering-committee members for feedback and potential modification. Afterwards, the committee reviewed the pilot survey results and comments. The pilot study results were NOT included in the analysis of data to determine consensus.

The final Round 1 survey consisted of 157 statements subdivided into six modules:  Module 1– Epidemiology & risk factors (20 statements); Module 2– Patient selection for metabolic and bariatric surgery (MBS, 29 statements); Module 3– Psychological issues (14 statements); Module 4– Patient preparation for MBS (23 statements); Module 5– Bariatric endoscopy (39 statements, only voted on by surgeons and endoscopists); and Module 6– Outcomes and follow-up (32 statements). Statements failing to achieve at least 70% consensus were included in a second-round survey. Each expert was asked at both the start and end of each module how comfortable they felt voting on the area of that module’s focus, rated from very uncomfortable to very comfortable. This was done to discourage voters from voting on statements they felt uncomfortable voting on; and so votes from uncomfortable voters could be excluded during data analysis. Note that the steering committee decided to define consensus with any particular statement as ≥70% agreement on the most commonly-selected response option; and to require at least 80% voting participation (≥80% of eligible voters) on any statement for that statement’s final vote tally to be considered valid.

The expert panel was intended to be intercontinental and inter-disciplinary, and to consist of practitioners with internationally-recognized expertise and extensive experience in obesity management. In June 2021, an email was sent to 100 experts who had previously agreed to participate in the survey, along with a link to the above-mentioned, committee-approved Round 1 survey on the online platform Survey Monkey. These experts spanned Africa, Asia, Europe, Latin America, the Middle East, North America, and Oceania, as well as the fields of bariatric endoscopy, bariatric surgery, general medicine, hepatology, psychology, and nutrition. Among the 100 experts invited to complete the survey, 94 did so within the 30-day time window allotted for Round 1 completion and were included in consensus analysis. Practice characteristics of these 94 are summarized in Table 1A, with practice characteristics of the n=37 bariatric surgeons and n=55 with experience in bariatric endoscopy summarized in Table 1-B.

Among the five modules open to all experts, the number of voters ranged from 80 to 94 (85-100%) out of 94; while, for Module 5, which was restricted to bariatric surgeons and endoscopists, the number of voters on statements ranged from 54 to 58 (94.7%-100%) out of 58. As such, no statement in any of the six Round 1 modules failed to achieve the minimum 80% to be considered a valid vote.

After Round 1 results were analysed, 23 statements – Module 2-Part B, on the ‘relative importance of pre-operative patient factors’ – were added to the Round 2 survey. Final analysis was, therefore, of 180 (157+23) statements.

Among the 180 statements included in the final analysis, only 17 (9.4%) were deemed by the advisory panel as favourable to a particular concept/belief/approach, 19 unfavourable (10.6%), and 144 (80.0%) non-judgmental (Table 2). Among these 180, 134 (74.4%) had the binary response options of agree/disagree, while 46 (75.6%) had other or more than two response options (e.g., more/less/about the same). An abbreviated third round of voting was conducted for the eight of 23 statements added to Round 2 for which no consensus was achieved in that round, thereby permitting two rounds of voting on all statements for which no consensus was achieved during the first vote.

At least 70% consensus was achieved on 158 statements (87.8%) – 114 in the first round and 44 in the second. However, 100% consensus was only achieved for 12 statements (6.7% of all statements, 7.6% of statements achieving consensus), with 80-89.9% consensus the most common result (37.8 and 43.0%, respectively). The average consensus per module was 83.6% overall, ranging from 78.0% for bariatric endoscopy to 87.9% for outcomes and follow-up (Table 2).

The results for each of the six modules are summarized individually in Tables 3 through 9, with Module 2 – on patient selection for MBS – subdivided into Part A (Table 4) and Part B (Table 5, consisting of the 23 statements added to Round 2, based upon responses to an open-ended question in Round 1). Each of these seven results tables lists each statement individually, along with, in successive columns from left to right, the number of experts who voted on it during the definitive round (whether Round 1 or 2);  the number of rounds required; the response option (e.g., agree/disagree) selected by the largest percentage of voters; the percentage of consensus ultimately achieved; and whether ≥70% consensus was reached. In these tables, statements are listed based upon the final level of consensus achieved, in decreasing order, with statements failing to achieve 70% consensus shaded to facilitate recognition.

On epidemiology and risk factors, unanimous consensus was reached that all medical societies need to address obesity systematically and that regular longitudinal national and regional surveillance is necessary. Strong consensus was achieved (a) defining obesity as a chronic disease that increases both morbidity and mortality risks; (b) that emotional eating is a common feature but (c) eating binges not universal among those with obesity; and (d) that ethnicity and geographical factors are both important pathophysiologically and when considering interventions.  The experts agreed that food addiction is a valid clinical entity, and common among patients undergoing MBS, especially among those with problematic alcohol and/or drug use. The experts were roughly evenly split on whether food addiction affects a great majority of patients considering MBS. There was agreement that binge eating is a risk factor for weight regain after MBS, but disagreement that it is a risk factor for suicidal ideations/attempts. Further results on epidemiology and risk factors are summarized in Table 3.

Pertaining to patient selection (Table 4), there was 100% consensus (a) that global rates of obesity are increasing in children and adolescents; (b) that obesity during childhood or adolescence portends obesity in adulthood;  (c) that severe obesity in the young portends significant obesity-related co-morbidity, like diabetes and hypertension; (d) that MBS in youths requires a multi-disciplinary team with experience dealing with youths and their families; and (e) that inadequate public and physician knowledge and scarce long-term results of MBS in youths are barriers to MBS use in the young. There also was near-unanimous agreement (98.9%) that life-long monitoring is necessary for youths who undergo MBS and that MBS in youths (95.6%) should be performed by experienced bariatric surgeons with a proven track record of success in adults. There also was agreement that enough empirical evidence has been published supporting MBS as the most effective therapy for severe obesity in youths and that MBS outcomes (positive and negative) in youths are similar to those achieved in adults.  In addition, certain MBS procedures, like biliopancreatic diversion (BD) and one-anastomosis gastric bypass (OAGB), should not be recommended for youths.

Considering seniors with obesity, there again was consensus agreement that MBS is generally effective and safe and increases quality of life and that age should not be the only consideration when deciding on surgery. Conversely, there was consensus that operating time is directly predictive of negative outcomes in seniors, and that seniors’ risks from MBS are greater than adolescents’. No consensus was reached concerning on the age when operative candidates should be considered elderly, on outcomes post Roux-en-Y gastric bypass (RYGB) and laparoscopic sleeve gastrectomy (LSG) relative to outcomes in adolescents, or on the gold standard MBS procedure for seniors. Table 5 ranks 23 pre-operative factors by their relative level of importance, with all but financial means and thyroid disease considered very important by ≥70% of our experts. Patients’ level of general health and fitness and the presence and/or nature of co-morbid illness were the two pre-operative factors selected as very important by the largest percentage of experts (98.7 and 97.5%, respectively).

Among psychological issues, there was consensus disagreement that patients undergoing MBS always develop problematic alcohol use or mostly experience worsened depression post-operatively. Experts also disagreed that those patients with pre-MBS cognitive depressive symptoms usually do not improve post-operatively, as opposed to those who have meaningful post-operative weight loss and usually experience improvement in their depression post MBS. That said, there also was consensus agreement that suicide is more common in patients who have undergone MBS. Strong consensus (93.6%) was reached that a comprehensive psychological evaluation is necessary pre-operatively, and that even patients with severe psychiatric illnesses – like schizophrenia or bipolar disorder – can undergo MBS if their psychopathology is well controlled.  Experts also agreed that patients with food addiction are more likely to have other psychiatric conditions – like depression and anxiety – than those without, and that cognitive behavioural therapy is the best therapeutic strategy for patients at high risk of binge eating. Further results regarding psychological issues are summarized in Table 6.

Pertaining to general health preparatory steps prior to MBS, consensus was reached on the need for comprehensive medical and nutritional evaluations, identification and correction of all nutritional deficiencies, smoking cessation, and pre-operative endoscopy, with sleep apnoea screening only necessary in those considered at high risk. Experts disagreed that routine computed tomography or magnetic resonance imaging is required to screen for hepatocellular carcinoma prior to MBS and that all anti-diabetic drugs reduce the risk of this cancer in patients with non-alcoholic fatty liver disease (NAFLD). Table 7 summarizes further results on both general health and anti-COVID 19 steps to take prior to MBS.

Among the 58 experts who reported performing endoscopic metabolic and bariatric therapy (EMBT), almost unanimous consensus was reached (a) on the unique and important roles these procedures have managing obesity, (b) that adequate endoscopic bariatric training is required for practitioners, and (c) that bariatric surgical centres should communicate a comprehensive care plan to patients and their primary care providers, including testing, supplements, and when to be referred back for re-evaluation. Table 8 also summarizes consensus opinions specifically regarding aspiration therapy, duodenal procedures, endoscopic gastric bypass, gastric plication, and suturing procedures, and intragastric balloons (IGB). Among these, the greatest support was expressed for IGB and least for aspiration therapy and duodenal bypass, with intermediate support expressed for gastric procedures involving bypass, plication, or suturing, depending on the situation. The only procedures for which currently-published empirical evidence was considered adequately supportive for them to no longer be considered of uncertain efficacy were those involving balloons. Intragastric balloons also were the only procedures considered acceptable for the sole purpose of helping patients “look better” and were felt to be acceptable “bridge therapy” for patients scheduled for later MBS.

Regarding post-procedural follow-up and outcomes, unanimous consensus was expressed that some degree of weight gain is normal 2-10 years after MBS, but also that appreciable post-operative weight gain may require further medical, endoscopic, or surgical treatment. Experts also unanimously agreed that post-MBS follow-up should be lifelong and that MBS centres should work jointly with patients' primary care providers to provide follow-up and access to appropriate healthcare professionals, as clinically indicated. Near-unanimous (98.7%) agreement was expressed on the potential need for further treatment in patients with continued severe obesity and obesity-related problems two years after MBS, and on the need for a comprehensive multi-disciplinary assessment in patients experiencing appreciable post-operative weight regain. Unsatisfactory post-operative weight loss was also considered an indication for supplementary medical treatment (e.g., glucagon-like peptide-1 agonist). However, 93.3% and 80.9% agreed, respectively, that no uniformly-recognized definitions exist for either “significant weight regain” or “surgical success”.

As for follow-up, nutrition counselling was considered an essential component of post endoscopic treatment by 98.9%, while assessing bone health and ruling out gastroesophageal dysfunction were considered important in patients deemed at high risk for osteoporosis and gastroesophageal reflux disease [32], respectively. Consensus agreement also was achieved on several statements pertaining to the benefits of MBS at a societal level. Further results on outcomes and follow-up are summarized in Table 9.

The clinical management of people with obesity has evolved tremendously over the past decade as a result of better understanding of this chronic disease. Such advances include more universal acceptance of obesity as a disease. Despite this, its prevalence continues to rise worldwide, and in all age groups[2-4]. In addition, the percentage of patients seeking any form of effective therapy for their obesity remains very low. There is widespread agreement, even beyond the current panel of experts, that a dire need exists to alter obesity’s current world trajectory and find ways both to prevent and treat it in more individuals. There were two options that scored unanimous consensus amongst all 94 members of our expert panel that might achieve both goals:  firstly, for all medical societies to cooperate to address the problem systematically; and, secondly, for longitudinal surveillance to be conducted routinely at both regional and national levels. Two examples of multinational obesity surveillance programs that have generated useful data have been the Scandinavian Obesity Registry (SOReg)[33] and German Bariatric Surgery Registry[34], the latter having existed for over 60 years. Such data have generated publications on such crucial issues as short-term and long-term outcomes after MBS and a 10-year post-operative mortality rate of just 0.06% over the first 90 post-operative days, as well as data on immediate and longer-term post-operative complications, weight loss, comorbidity management, the impact of patient age on outcomes, and comparing different MBS procedures[33-41]. Though such data are of tremendous value, only a very small percentage of individuals with obesity ever undergo bariatric surgery, and it is the remaining huge majority for which closer surveillance remains necessary. More realistic, perhaps, are physician and public obesity education campaigns designed to increase awareness both about the health hazards associated with obesity, (e.g., the increased risk of contracting several forms of cancer), and the need for comprehensive, multidisciplinary treatment, especially for those whose obesity has become severe and those with obesity-associated comorbidities.

Another issue on which unanimous consensus was repeatedly reached was obesity in children and adolescents, with 100% of our experts agreeing that global rates of obesity are currently increasing in these two youth populations and that most youths with obesity continue to have obesity in adulthood. Additionally, youths with severe obesity are at risk of significant obesity-related comorbidities, such as diabetes.  Furthermore, there was unanimity that MBS in adolescents requires an experienced, multi-disciplinary team with experience dealing with youths and their families, and that inadequate physician and public awareness and insufficient long-term outcome data are barriers against the referral of adolescents who might benefit from MBS. Pertaining to insufficient data, five meta-analyses documenting the beneficial effects of MBS in adolescents (including sustained weight reduction, improvements in some obesity-related comorbidities, especially T2DM, and improved quality of life) have been published[42-46]. However, few studies included in the analysis had follow-up beyond five years and virtually none followed youths into adulthood. Data also are scant on potential nutritional and developmental difficulties[46].

In our survey, unanimous consensus was reached on five additional statements, all pertaining to surgical treatment or post-surgical follow-up. Unanimously-expressed opinions were (1) that multidisciplinary assessment is necessary prior to MBS, [28] that some degree of weight regain is normal from 2-10 years after MBS; (3) that significant weight regain, or the presence/persistence of obesity-related medical problems may require further medical, endoscopic, or surgical treatment, (4) that follow-up after MBS should be lifelong, and (5) that MBS centers should work jointly with their patients’ primary healthcare providers to ensure adequate follow-up and access to other healthcare professionals, as indicated. Regarding MBS patient selection, the pre-operative factors rated very important by almost all (95%) experts were the patient’s overall level of health and fitness, the presence and/or nature of comorbid illness, patients’ cognitive ability to understand the procedure and instructions, and the presence of either alcohol or some other substance abuse.

Repeatedly expressed in our results was the need for multiple healthcare practitioners spanning different disciplines, especially for patients considering MBS. This should begin with a multi-disciplinary pre-operative assessment to determine each patient’s eligibility for MBS.  Such an assessment also is necessary to identify co-morbid medical, nutritional, and psychological disorders or barriers to treatment success and attempt to address as many of these barriers pre-operatively as possible. Also necessary is to otherwise prepare patients for surgery, including educating them concerning realistic goals, potential post-operative symptoms, the high likelihood of some weight regain or other set-backs and, perhaps most importantly, the need for continued, life-long follow-up. This multimodal management requires collaboration from members of a multidisciplinary team that includes dieticians/nutritionists, behavioural therapists, physicians, endocrinologists, endoscopists, and surgeons.

Following surgery, patients continue to require ongoing, multi-disciplinary care to manage their weight loss program and obesity-associated comorbidities.  In addition, patients require monitoring for the life-altering effects of surgery, like the risk of potentially-catastrophic nutritional deficiencies that may vary depending on the specific MBS performed[22, 47]. Each patient’s psychological state must also be followed, given recent data suggesting an albeit only slightly elevated risk of suicide in both adolescents and adults who undergo MBS[48, 49]. Potential contributory factors include forced alterations in foods they can and cannot eat, gastrointestinal symptoms secondary to food intolerance, and unrealized, unrealistic expectations about the extent of weight loss they may experience post-operatively, leading to depression, anxiety, a reduced sense of self-worth, and other forms of psychological distress. Monitoring also is essential to detect the re-emergence of detrimental eating patterns, like binge eating, as one recently-published meta-analysis has shown these factors to be predictive of poorer post-operative weight management[50].

Every expert consensus survey has the potential for bias, given that participants may already have a predilection to utilize a particular practice to have become experts in its use. In addition to adopting the Delphi approach (characterized by voter anonymity and, thus, largely eliminating acquiescence bias), our survey was unique in that we sought the opinions of a uniquely-broad array of healthcare practitioners that included surgeons, non-surgical physicians, as well as non-physician experts in nutrition and psychological counselling.   All participants were invited to vote on any statement with which they felt comfortable, except for one module on endoscopic therapy, which was restricted to surgeons and endoscopists. Recognizing worldwide differences in obesity management, we also included experts from every permanently-inhabited continent, including the Middle East. In this manner, we attempted to minimize the widely-held criticisms of consensus-survey critics of “like-minded individuals voting together”. We further worded survey statements to be balanced, with a sizeable majority neither favoring nor opposing the concept/belief/approach presented, and the remaining statements evenly balanced between favorable and unfavorable.  In addition, the order of response options was altered so the most favorable option was listed anywhere from first to last.

We nonetheless acknowledge that consensus surveys are level-V evidence, and based upon opinions, rather than experimentally-generated data. On the other hand, all our voters were widely-renowned experts in obesity management, all but 10% university affiliated and contributing to such research, and were, thus, both familiar with said research and, likely, most qualified to interpret it. In other words, their opinions were based not just upon their extensive experience, but on their expansive knowledge of relevant research. Moreover, as stated initially, the current consensus survey was conducted to aid in generating joint IFSO:WGO guidelines, for which almost 1000 scientific references have also been utilized to frame the discussion. The consensus opinions we sought to aid in drafting those guidelines were for issues in which existing literature is either non-definitive – requiring appreciable interpretation – or largely lacking, especially on issues that might be particularly difficult to study empirically, like whether endoscopic therapy can be justified for aesthetic purposes only.

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