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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