Recent advances in metabolic and bariatric surgery

Abstract

Obesity and its associated medical conditions continue to increase and add significant burden to patients, as well as health-care systems, worldwide. Bariatric surgery is the most effective treatment for severe obesity and its comorbidities, and resolution of diabetes is weight loss-independent in the case of some operations. Although these weight-independent effects are frequently described clinically, the mechanisms behind them are not well understood and remain an intense area of focus in the growing field of metabolic and bariatric surgery. Perceptions of the mechanisms responsible for the beneficial metabolic effects of metabolic/bariatric operations have shifted from being mostly restrictive and malabsorption over the last 10 to 15 years to being more neuro-hormonal in origin. In this review, we describe recent basic and clinical findings of the major clinical procedures (adjustable gastric banding, vertical sleeve gastrectomy, Roux-en-Y gastric bypass, and biliopancreatic diversion) as well as other experimental procedures (ileal interposition and bile diversion) that recapitulate many of the metabolic effects of these complex operations in a simpler fashion. As the role of bile acids and the gut microbiome on metabolism is becoming increasingly well described, their potential roles in these improvements following metabolic surgery are becoming better appreciated. Bile acid and gut microbiome changes, in light of recent developments, are discussed in the context of these surgical procedures, as well as their implications for future study.

Keywords: Bariatric surgery; Metabolic surgery; Morbid obesity; Roux-en-Y gastric bypass; adjustable gastric banding; bile diversion; biliopancreatic diversion; ileal interposition; vertical sleeve gastrectomy.

Figure 1.. Adjustable gastric banding.

In this procedure, an external ring is placed around the proximal portion of the stomach and has a balloon that lines the inside portion of the ring. The inflatable balloon is connected to a port in the subcutaneous tissue of the abdomen that allows the balloon volume, and therefore the amount of gastric restriction, to be adjusted.

Figure 2.. Vertical sleeve gastrectomy.

A majority of the greater curvature is excised in this procedure, creating a tube-like stomach with a marked reduction in gastric capacity.

Figure 3.. 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.

Figure 4.. Biliopancreatic diversion.

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.

Figure 5.. Ileal interposition.

A neurovascular intact segment of distal or near-terminal ileum is interposed in the proximal jejunum near the ligament of Treitz. The distal jejunum is then re-anastomosed to the small segment of ileum proximal to the ileocecal valve to re-establish bowel continuity.

Figure 6.. Bile diversion.

In the absence of any gastric restriction, the common bile duct is ligated proximal to the pancreatic duct and an anastomosis is created between a portion of ileum and the gallbladder. Pancreatic secretions follow their normal course and drain into the duodenum, but biliary secretions are diverted to the portion of ileum connected directly to the gallbladder.