We searched PubMed for reports published in English up to Aug 1, 2013. The search terms “bariatric surgery”, “gastric bypass”, “sleeve gastrectomy”, “gastric banding”, “biliopancreatic diversion” were used alone and in combination with “diabetes mellitus”, “β-cell function”, “insulin resistance”, “weight loss”, “appetite”, “energy expenditure”, “caloric restriction”, “bile acids”, “microbiota”, “gene polymorphism”, and “future treatment”. We also manually searched the relevant scientific
SeriesMechanisms of changes in glucose metabolism and bodyweight after bariatric surgery
Introduction
The increasing prevalence of obesity has generated a secondary epidemic of metabolic syndrome—ie, abdominal obesity with increased risk of type 2 diabetes and cardiovascular diseases.1, 2 Additional metabolic comorbidities include polycystic ovary syndrome and non-alcoholic steatohepatitis. Obesity is also associated with obstructive sleep apnoea and several cancers.1 Abdominal obesity and ectopic fat deposits in the liver, pancreas, and skeletal and heart muscle can lead to insulin resistance.2 Obesity can also cause suppression of adiponectin and increases in concentrations of fatty acids, proinflammatory cytokines (including tumour necrosis factor [TNF] and interleukin 6), and fibrinogen—all of which contribute to insulin resistance, pancreatic β-cell dysfunction, and low-grade inflammation in the vascular system, with increased C-reactive protein and plasma activator inhibitor 1.2
Treatment of obesity with lifestyle changes focused on weight loss and increased physical activity can cause patients to lose 5–10% of their bodyweight, but most will start to regain weight after 3–9 months, and after 1–5 years about 90% will have returned to their original weight, or might even weigh more than before the intervention.3 Addition of anti-obesity drugs to lifestyle changes can add a further weight loss of 2–8 kg.3 By contrast, bariatric surgery effectively treats obesity and its comorbidities through radical effects on energy intake and glucose metabolism. Notably, in some cases, improvement in glycaemic control after bariatric surgery in people with type 2 diabetes occurs within days of surgery and before any weight loss, and the effect is also seen in mildly overweight patients.4, 5 The International Diabetes Federation advocates bariatric surgery for the treatment of subgroups of patients with type 2 diabetes.6 Roughly 350 000 bariatric operations are done worldwide every year.5 Laparoscopic Roux-en-Y gastric bypass (RYGB) is the most common bariatric procedure, followed by vertical sleeve gastrectomy (VSG) and laparoscopic adjustable gastric banding (LAGB), with VSG becoming increasingly popular.7 Biliopancreatic diversion (BPD) with duodenal switch is used less often than the other procedures.7
In this Series paper, we explore the possible mechanisms underlying the metabolic effects of bariatric surgery, with a focus on weight loss and resolution of type 2 diabetes. We also discuss less invasive surgical procedures and other therapeutic strategies for obesity and type 2 diabetes inspired by bariatric surgery that might be used increasingly in the future. We focus mainly on studies of LAGB, RYGB, and VSG in human beings.
Section snippets
Effects of bariatric surgery on bodyweight and type 2 diabetes
The large range of bariatric procedures and their development have been reviewed elsewhere.8 Briefly, the operations have traditionally been divided into restrictive procedures, including LAGB and VSG, and those that induce bypass of one or more segments of the gastrointestinal tract, such as RYGB (figure 1).
Bariatric surgery produces major and durable weight loss. In Buchwald and colleagues' meta-analysis,9 weight loss (expressed as percentage of excess weight) averaged 47% after LAGB, 62%
Gastric restriction
Physicians initially speculated that weight loss after bariatric surgery was due to mechanical restriction and, for procedures that involve bypass, malabsorption of foods.8 Subsequently, the focus of research has shifted towards the metabolic effects of the surgeries. Some of the most important mechanisms underlying weight loss and remission of type 2 diabetes after LAGB, VSG, and RYGB are summarised in the table.
LAGB has traditionally been regarded as a restrictive procedure, but Burton and
Weight loss
LAGB, RYGB, and VSG seem to induce weight loss by partly overlapping mechanisms. None of these procedures should be regarded as restrictive, including LAGB. Optimally adjusted LAGB only briefly delays the passage of semisolid food through the band, and the gastric and intestinal transit of food is normal.21 As discussed, distension stimuli from the small pouch could be transmitted via vagus afferents to areas of the central nervous system implicated in satiety.22 No hormonal changes account for
Future prospects
Less invasive treatments that mimic the effects of bariatric surgery are of interest for the treatment of obesity and type 2 diabetes. However, so far, the positive effects of surgery have not been replicated by any medical treatment. Targeting two or more anorexigenic pathways might be necessary to achieve substantial weight loss. The GLP-1 receptor agonists are very effective for the treatment of type 2 diabetes, inducing a reduction in HbA1c greater than oral antidiabetic drugs, together
Conclusions
Obesity and type 2 diabetes are closely linked health problems. No existing dietary or exercise regimen can restore and sustain a healthy bodyweight for an extended period in most obese patients. The only available intervention with curative potential is bariatric surgery, which is invasive, often irreversible, and has associated risk. Such surgery cannot be delivered on a mass scale and is currently reserved for severely obese individuals.
Bariatric surgery was originally designed for weight
Search strategy and selection criteria
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