Obesity is a significant health-care problem with few treatment options, many of which are only minimally effective in the long term. Medical therapy consisting of intensive lifestyle modification (that is, diet, exercise, and behavioral therapy) fails to maintain significant long-term weight loss. Although medical intervention can lead to modest weight loss in select patients , 5–10% weight loss in a morbidly obese individual still leaves that patient with significant cardiometabolic risk.
Metabolic and bariatric surgery (in this review, the phrase “metabolic and bariatric surgery” refers to a single entity) is recognized as the most effective treatment for obesity and its associated comorbidities, such as type 2 diabetes and its usage continues to increase with the increasing prevalence of obesity and metabolic disease.Overall, the benefits of bariatric and metabolic surgery continue to be better described, particularly the decreases in cardiovascular disease and cancer mortality. With the alleviation of diabetes and other comorbidities, it is not surprising that bariatric surgery also exhibits cost savings compared with chronic medical treatment of these diseases.
(A)Purely restrictive operations
Adjustable gastric banding and gastric balloons
The contribution of gastric restriction to the efficacy of bariatric surgery is an area that has been well studied clinically and experimentally. The adjustable gastric band and gastric balloons are two procedures that purely decrease the capacity of the stomach, by either an adjustable external compressive device (that is, the adjustable gastric band) or merely taking up space within the stomach (that is, the gastric balloon). Over the last decade, adjustable gastric banding has continued to fall from its peak clinical usage in 2008 to currently comprising only 10% of bariatric procedures worldwide. This decline is due to the relative ineffectiveness of banding for long-term weight loss and reduced comorbidity compared to other bariatric procedures.
(B)More than gastric restriction: operations with hormonal effects
Without a doubt the most exciting advancements in the field of metabolic and bariatric surgery over the last decade have been the identification of mechanisms that have challenged the long-held beliefs that “bariatric” surgical procedures induce weight loss purely through a combination of gastric restriction or nutrient malabsorption, or both. Neural, hormonal, and other nutrient signaling pathways that have previously been unrecognized may be mediating many of the metabolic benefits of these surgical procedures.
- Vertical sleeve gastrectomy
The vertical sleeve gastrectomy is a surgical procedure that decreases gastric volume by approximately 70% with excision of a large portion of stomach along the greater curvature .A majority of the greater curvature is excised in this procedure, creating a tube-like stomach with a marked reduction in gastric capacity.
As mentioned above, clinical and experimental evidence has demonstrated that gastric restriction alone is not effective as a long-term solution for obesity or its comorbidities.
(b)Roux-en-Y gastric bypass and biliopancreatic diversion
The RYGB and BPD operations combine significant intestinal rearrangement with gastric restriction. Each procedure involves creation of a smaller stomach pouch while diverting nutrient flow to varying distal segments of the intestine. The gastric restrictive component is typically less with BPD but diversion of biliopancreatic secretions is more distal, compared with RYGB.
Roux-en-Y gastric bypass
The stomach is divided, creating a small gastric pouch that is connected through a gastro-jejunostomy to a distal segment of jejunum, which forms the Roux limb of the procedure. The remainder of the stomach is referred to as the “gastric remnant” and drains into the bypassed portion of bowel, referred to as the “biliopancreatic limb”. Bowel continuity is restored for the biliopancreatic limb by a jejuno-jejunostomy that creates the “Y” configuration of the operation. Thus, ingested nutrients proceed rapidly through the stomach pouch and move immediately into the jejunal Roux limb in the absence of bile and pancreatic secretions. Bile and pancreatic secretions drain via the biliopancreatic limb and then mix with the chyme/nutrients at the point of the jejuno-jejunostomy.
This is a procedure that effectively diverts bile and pancreatic secretions to the distal bowel for mixing with nutrients/chyme, typically much further distal than a Roux-en-Y gastric bypass. This procedure can be performed with or without a partial gastrectomy and is also referred to as a duodenal switch; the “switch” is the diversion of bile and pancreatic secretions from nutrient flow.