Open Access
Feature Article

Bariatric surgery: positive and negative effects

Open Access
Feature Article

Bariatric surgery: positive and negative effects

Eddy J. Tabet, Ian D. Caterson, Tania P. Markovic

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© BSIP RF/DIOMEDIA.COM
© BSIP RF/DIOMEDIA.COM
Dr Tabet is a Staff Specialist in the Department of Endocrinology at Royal Prince Alfred Hospital; and Clinical Associate Lecturer at The University of Sydney, Sydney. Professor Caterson is the Boden Professor of Human Nutrition and Director of The Boden Collaboration for Obesity, Nutrition, Exercise & Eating Disorders at The University of Sydney, Sydney; and an Endocrinologist at Royal Prince Alfred Hospital, Sydney. Dr Markovic is Director of Metabolism and Obesity Services at Royal Prince Alfred Hospital, Sydney; and Clinical Associate Professor, Boden Collaboration for Obesity, Nutrition, Exercise & Eating Disorders at The University of Sydney, Sydney, NSW.

Type 2 diabetes

Although the metabolic benefits of weight loss induced by bariatric surgery are well documented, only few patients with type 2 diabetes are offered this therapy. It could be argued that the risk of mortality from diabetes itself far outweighs the risk of mortality at expert centres performing bariatric surgery – a surgical mortality rate of 0.44% for RYGB was reported in a 2015 review.11 The rapidity of the effect on glucose homeostasis after RYGB or LSG implies that it is mediated independently of the weight loss. In contrast, improvements in glucose regulation after LAGB are entirely dependent on weight loss. Hyperinsulinaemic–euglycaemic clamp studies have demonstrated an increase in insulin sensitivity with LSG and RYGB compared with LAGB; whether this is due to the greater weight loss achieved with these procedures or to hormonal changes is unclear. LSG and RYGB have each been shown to induce changes in gut hormones, such as glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide, as well as insulin, which can reduce postprandial glucose levels.12,13 GLP-1 also assists with appetite control by inhibiting gastric emptying and acting centrally to reduce food intake. These procedures have also been shown to increase another anorectic hormone, peptide YY, and to decrease the orexigenic hormone ghrelin, at least in the short term.13 

Several high-quality randomised controlled trials have shown significant rates of diabetes remission at one or two years, with positive although lesser rates of remission at three to five years’ follow up. The type 2 diabetes remission rates observed in these clinical trials are summarised in Table 2.14-19 In an Australian study conducted in patients with diabetes of shorter duration (less than two years), a remission rate of 73% was observed two years after LAGB compared with 13% after conventional therapy.14 In one of these trials, a single-centre open-label study of patients with diabetes (over more than five years) in Italy, the diabetes remission (defined as fasting glucose level below 5.6 mmol/L and HbA1c below 6.5% [<48 mmol/mol] while off glucose lowering medication for at least 12 months) rate was 75% in patients treated with RYGB and 0% in patients treated with conventional medical therapy at two years.15 At five years, 37% of the RYGB group maintained remission compared with none of the medically treated patients.16 (This study also included a group undergoing biliopancreatic diversion, a procedure that is now rarely performed in Australia.) In a study with three sites in the US and one in Taiwan in which 120 people with diabetes (mean HbA1c 9.6% [81 mmol/mol], approximately 50% taking insulin) were randomised to RYGB or intensive medical management, 35% of those who had a RYGB were in remission (defined as HbA1c below 6.5% [48 mmol/mol] while off glucose lowering therapy for at least 12 months) at two years and 16% at five years, whereas none of the patients on medical management alone achieved remission at either time point.17

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In the STAMPEDE trial, a randomised, nonblinded, single centre trial in the US comparing bariatric surgery with intensive medical therapy for diabetes (n = 150), at one year after randomisation 42% of patients undergoing RYGB and 37% of patients undergoing LSG achieved the primary endpoint (HbA1c less than 6% [<42 mmol/mol] whether or not on glucose lowering therapy, a more lenient endpoint than the preceding studies) compared with 12% of patients receiving medical therapy alone.18 At five years the respective figures were 29% for those who had RYGB, 23% for LSG and 5% in those who received medical therapy alone.19 The average duration of diabetes in the STAMPEDE study population was 8.3 years; at baseline, the mean HbA1c was 9.3% (78 mmol/mol) and 43% of patients were taking insulin.18 Overall, the predictors of diabetes remission with bariatric surgery appear to be lower fasting glycaemia at baseline, shorter duration of diabetes and procedures that divert gastric contents into the small intestine, such as RYGB.20

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