Our understanding on the short‐ and long‐term evidence based on various bariatric surgical procedures has substantially improved. In addition to the well‐recognised metabolic benefits of bariatric surgery, evidence on the non‐metabolic benefits of bariatric surgery has also become more widely recognised. This chapter focuses on the non‐metabolic effects of bariatric surgery, specifically on obesity‐related co‐morbidities outcomes related to weight loss, cardiovascular disease, sleep apnoea, osteoarthritis, mental health, quality of life, as well as other outcomes, such as urine incontinence and cancer risk.

Weight Loss

Bariatric surgery results in greater short‐ and long‐term weight loss than any best available non‐surgical interventions for obesity, irrespective of the type of bariatric procedure used. While many medical weight‐loss programmes have reported substantial weight loss, a very few have reported durability beyond two years. Two of the most widely quoted medical weight‐loss programmes, from which much of the weight‐loss intervention are based on, are the Diabetes Prevention Program and Look AHEAD studies. The latter, however, reported a modest effect of 6% total weight loss at a median follow‐up of 9.6 years.

The lack of standardised reporting of weight loss has somewhat complicated the assessment of weight loss reported from different bariatric surgery studies. In different studies, weight loss is reported or expressed in (i) percentage of weight loss (in kg or BMI), (ii) mean change in weight (in kg or BMI) and (iii) percent excess weight loss (EWL), which is defined as ([initial weight] − [post‐operative weight])/([initial weight] − [ideal weight]), where ideal weight is defined by the weight corresponding to a BMI of 25.

There remains ongoing debate regarding the most effective bariatric surgical procedures to induce the greatest weight loss. As a whole, RCTs comparing different bariatric surgery procedures have shown that patients undergoing RYGB and sleeve gastrectomy experienced similar weight loss, which are greater than the weight loss observed in patients who underwent gastric banding (LAGB) (Figure 22.1). A randomised study comparing gastric bypass (RYGB) versus sleeve gastrectomy (LSG) published in December 2020 showed that at seven years the estimated mean %EWL was 47% (95%CI, 43–50%) in the LSG group and 55% (95% CI, 52–59%) in the LRYGB group. The model‐based estimate of mean %EWL was 8.7 percentage units (95% CI, 3.5–13.9 percentage units) higher after LRYGB than after LSG. Although weight loss after LRYGB was statistically greater compared with LSG, the difference was not clinically relevant with respect to the predefined 95% CIs and equivalence margin. This finding supported previous systematic reviews that found no significant difference in BMI reduction comparing RYGB vs LSG (−0.76 [95% CI, 1.6 to −3.1]). Another systematic review with meta‐analysis that included only studies containing 10 or more years of follow‐up data on weight loss after bariatric surgery was reported. Their analysis of 18 reports of RYGB showed a weighted mean of 56.7% EWL, 17 reports of LAGB showed 45.9% EWL and 2 reports of LSG showed 58.3% EWL. Meta‐analyses of eligible studies showed comparable results, thus showing significant and durable weight loss with bariatric surgery (Table 22.1). The most effective outcomes however came from the biliary pancreatic diversion or its variant with a pooled effects size of ~71% EWL. This procedure however is not widely used now due to higher risks of long‐term metabolic complications. In contrast to evidence from RCT, observational studies however showed that RYGB is associated with greater weight loss than sleeve gastrectomy. For example, the PCORnet Bariatric Study compared weight‐loss outcomes of 32 208 RYGB patients, 29 693 LSG patients, and 3192 AGB patients from 41 health systems in the United States. They reported a five‐year mean % total weight loss of 25.5% (95% CI, 25.1–25.9%) for RYGB, 18.8% (95% CI, 18.0–19.6%) for LSG and 11.7% (CI, 10.2–13.1%) for AGB. Simple conclusions however cannot be made with observational studies due to inherent limitations of confounding factors and biases – most importantly, allocation bias. Importantly, however, evidence from observational study can provide insights on weight regain from bariatric surgery. To this end, the PCORnet Bariatric Study found that this occurred in 3.3% of RYGB patients, 12.5% of those with sleeve gastrectomy and 36.0% of AGB patients at five‐year follow‐up.

Cardiovascular

As discussed previously, obesity is associated with an increased risks of a plethora of cardiovascular‐related diseases. While previous RCT have shown that bariatric surgery leads to significant improvements in diabetes and cardiovascular risk factors, none of these trials were adequately powered to evaluate the effects of bariatric surgery on mortality and other major cardiovascular events. As such, our understanding of the effects of bariatric surgery on cardiovascular outcomes and total mortality is limited to evidence derived from observational studies. (Figure 22.2). The Swedish Obesity Study (SOS) was perhaps the first large‐scale observational study with extensive follow‐up data to report on cardiovascular outcomes. The study included 2010 obese participants who underwent bariatric surgery and 2037 contemporaneously matched obese controls who received usual care. In this study, bariatric surgery was associated with a reduced number of cardiovascular deaths adjusted hazard ratio ([HR], 0.47; 95% CI, 0.29–0.76; P = 0.002). The number of total first‐time (fatal or non‐fatal) cardiovascular events (myocardial infarction or stroke, whichever came first) was lower in the surgery group (199 events amongst 2010 patients) than in the control group (234 events amongst 2037 patients; adjusted HR, 0.67; 95% CI, 0.54–0.83; P < 0.001). Further studies have also reported reductions in cardiovascular events amongst obese patients with type 2 diabetes who underwent bariatric surgery. In one study, 5301 patients who underwent bariatric surgery were matched to 14 934 control patients. Bariatric surgery was associated with a lower composite incidence of macrovascular events at five years (2.1% in the surgical group versus 4.3% in the non‐surgical group; hazard ratio, 0.60 [95% CI, 0.42–0.86]) as well as a lower incidence of coronary artery disease (1.6% in the surgical group versus 2.8% in the non‐surgical group; hazard ratio, 0.64 [95% CI, 0.42–0.99]). Stroke rate was not significantly different. A further study involving 2287 patients with diabetes who underwent metabolic surgery versus 11 435 matched control patients reported similar benefits in favour of bariatric surgery. The primary outcome of MACE, defined as the first occurrence of all‐cause mortality, coronary artery events, cerebrovascular events, heart failure, nephropathy or atrial fibrillation, was significantly reduced in patients who underwent bariatric surgery by about 39% (adjusted hazard ratio [HR], 0.61 [95% CI, 0.55–0.69]). All‐cause mortality was also reduced by 41% (HR, 0.59 [95% CI, 0.48–0.72]). All secondary end points that included three‐component major adverse cardiovascular event (MACE; myocardial infarction, ischemic stroke and mortality) also showed statistically significant differences in favour of metabolic surgery. More recently, the benefits of bariatric surgery to reduce MACE amongst patients with cardiovascular disease was reported. In this study, patients with previous ischemic heart disease or heart failure who received bariatric surgery were matched on age, sex and heart failure history to similar controls from a primary care medical record database in a 1:1 ratio. A total of 2638 patients (n = 1319 in each group) were included, with a median follow‐up time of 4.6 years. The occurrence of MACE (first occurrence of all‐cause mortality, myocardial infarction, coronary revascularisation, cerebrovascular events and heart failure hospitalisation) was significantly reduced by 42% in the bariatric surgery group (adjusted hazard ratio [HR], 0.58 [95% CI, 0.48–0.71]; P < 0.001). The association was particularly notable for those with heart failure and in those with ischemic heart disease. Surgery was also associated with a lower incidence cardiovascular mortality (HR, 0.35 [95% CI, 0.15–0.80]; P = 0.001) (Figure 22.3).

Obstructive Sleep Apnoea

While continuous positive airway pressure remains to be the main stay of treatment for obstructive sleep apnoea (OSA), excess weight is the main pathogenic factor that drives the development of OSA. Not surprisingly, weight loss has been shown to improve sleep disordered breathing and should be the holistic management strategy for patients with OSA. Untreated OSA is associated with a decline in quality of life and increased risks of developing various cardiovascular co‐morbidities, such as ischaemic heart disease, hypertension, pulmonary hypertension and stroke.

Various meta‐analyses have reported that bariatric surgery was associated with significant reductions in the severity of sleep apnoea – expressed as the apnoea–hypopnea index (AHI) scores (normal <5, mild 5–14.9, moderate 15–29.9 and severe >30 events hour⁻¹). Overall, meta‐analyses have reported a significant reduction of AHI from 39.3 to 12.5 events hour⁻¹

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