Introduction
Bariatric surgery encompasses a range of operative procedures that aim to promote sustained weight loss and improve metabolic health by altering the anatomy and physiology of the gastrointestinal tract.
Each procedure has its own implications in terms of anatomical reconstruction, physiological response, risk profile, and long-term outcomes. As an overview, bariatric operations achieve weight loss through three main mechanisms: restriction, malabsorption, and hormonal changes.
Mechanism of Weight Loss
Bariatric surgery leads to weight loss through a combination of restrictive, malabsorptive, and hormonal mechanisms
- Restrictive procedures, such as sleeve gastrectomy and gastric banding, reduce the size of the stomach, limiting food intake and promoting early satiety
- Malabsorptive procedures, such as the Roux-en-Y gastric bypass and biliopancreatic diversion, alter anatomy so that food bypasses a significant portion of the small intestine, reducing nutrient absorption
Additionally, bariatric procedures can induce significant hormonal changes to contribute to weight loss, such as with changes to ghrelin (may reduce, suppressing appetite) leptin (may increase, promoting satiety), and GLP-1 (may increase, enhancing insulin sensitivity and appetite regulation) levels
Gastric Band
Adjustable gastric banding is a purely restrictive procedure, though its use has declined in recent years due to inferior long-term outcomes and re-operative rates*.
A prosthetic band is placed laparoscopically around the upper part of the stomach, creating a small proximal pouch with a narrow outlet to the distal stomach. The band is connected to a subcutaneous access port which allows adjustment of band tightness through percutaneous saline injections.
Key complications include band slippage, band erosion, and injection port site issues.
*Whilst its use is decreasing in certain countries, it remains relevant due to its continued use in many other countries and the presence of legacy patients with bands in situ
Figure 1 – Illustration showing a gastric band procedure
Sleeve Gastrectomy
The sleeve gastrectomy (also known as a gastric sleeve) is a commonly performed bariatric procedure that involves the longitudinal resection of the stomach, converting it to a narrow tubular structure with a reduced capacity.
Typically performed laparoscopically, the greater curvature of the stomach is mobilised and a large bougie passed alongside the lesser curvature. Stapling is then performed proximal to the pylorus up to the angle of His, excising approximately 75-80% of the stomach.
Anatomically, the resultant gastric sleeve that is left typically has a volume of approximately 100-150mL. Resection of the gastric fundus, a key site of ghrelin (the “hunger hormone”) production further leads to reduced appetite, whilst the preservation of the pylorus allows for normal gastric emptying. As the small intestine remains unaltered, sleeve gastrectomy achieves weight loss through restrictive and hormonal mechanisms, without inducing malabsorption.
Key complications include staple line leak and failure to lose weight.
Figure 1 – Illustration showing the anatomy following a sleeve gastrectomy procedure
Roux-en-Y Gastric Bypass
Roux-en-Y gastric bypass (RYGB) is a restrictive and malabsorptive procedure that also induces hormonal changes, contributing to weight loss and improved metabolic control.
The operation is typically performed laparoscopically. A gastric pouch is created by dividing the cardia from the rest of the stomach via a stapler passed through a window in the lesser sac. The jejunum is then divided approximately 50cm distal to the ligament of Treitz. The distal jejunal limb is anastomosed to the gastric pouch, forming the Roux (alimentary) limb. The proximal jejunal limb is reconnected 75-150cm downstream via a jejunojejunostomy, forming the biliopancreatic (or “Y” limb).
Mesenteric defects are closed to reduce the risk of internal herniation, and an intraoperative leak test, using methylene blue via a nasogastric tube, can be performed prior to closure.
This anatomical configuration results in the bypass of the majority of the stomach, duodenum and proximal jejunum, leading to a degree of malabsorption. The small gastric pouch further restricts intake, whilst hormonal changes (including reduced ghrelin and increased GLP-1 and leptin) reduce appetite, increase satiety, and improve glycaemic control.
Key complications include internal herniation, marginal ulcers, and dumping syndrome. The expected loss of excess weight is approximately 70% at 2 years post-op RYGB.
Figure 1 – Illustration demonstrating the anatomy of a gastric bypass procedure
Biliopancreatic Diversion with Duodenal Switch (BPD-DS)
BPD-DS is a complex bariatric procedure combining both restrictive and malabsorptive elements to achieve weight loss, particularly in patients with severe obesity.
The procedure begins with a sleeve gastrectomy, as previously described, creating a narrow gastric pouch. The duodenum is then divided just distal to the pylorus, and a portion of ileum is brought up and anastomosed to the duodenal stump via a duodenoileostomy. The remaining proximal small bowel is bypassed, and the biliopancreatic limb is connected to the downstream small bowel.
The gastric sleeve provides restrictive weight loss by limiting food intake, while the malabsorptive aspect of the procedure arises from bypassing most of the small intestine, severely reducing the surface area for nutrient absorption.
Key Points
- Bariatric surgery promotes weight loss through three main mechanisms: restriction, malabsorption, and hormonal changes
- Patients undergoing malabsorptive procedures will require lifelong supplementation of micronutrients including iron, calcium and vitamins
- Each bariatric procedure carries its own set of specific complications, which must be considered when assessing patients with a history of bariatric surgery who present with abdominal pain
