Mechanisms of weight loss and postoperative complications after bariatric surgery

After bariatric surgery, food absorption decreases with a reduction in adipose tissue, which is accompanied by improved insulin sensitivity. After operations with rapid delivery of nutrients to the distal small intestine (RYGB, DS, and especially MGB-OAGB), remission of type 2 diabetes mellitus (T2DM) occurred in approximately 80–95% of patients. Undigested food stimulates the release of incretins (food-stimulated intestinal hormones that stimulate β-cells) into the bloodstream. Glucagon-like peptide-1 (GLP-1), produced by L-cells of the ileum, induces proliferation of pancreatic β-cells. In addition, bariatric surgery is performed to treat T2DM in patients with less than morbid obesity in order to ensure rapid transit of food to the ileum.

An important hormone in weight regulation is ghrelin (growth hormone-releasing hormone). Ghrelin is secreted by the stomach during fasting and stimulates food intake. After bariatric procedures involving gastric resection, plasma ghrelin levels decrease.

In patients with obesity, low serum vitamin D3 levels and even secondary hyperparathyroidism are often observed preoperatively. This may be related to insufficient exposure of the skin to sunlight. After most bariatric procedures, supplementation with vitamin D3, calcium, and iron is required. Metabolic bone diseases may worsen after surgery when ingested calcium compounds do not receive sufficient gastric acid for their breakdown.

After restrictive procedures, patients may experience difficulty chewing red meat in order to pass it through the narrowed, formed stomach.

After operations that bypass the duodenum (where iron absorption normally occurs), iron deficiency anemia may develop, especially in menstruating women after RYGB and MGB- OAGB.

After gastric bypass or sleeve gastrectomy, vitamin B12 supplementation is indicated, since the site of intrinsic factor production (the gastric fundus) is largely removed.

Folic acid supplementation is necessary during restricted oral intake, especially in women of reproductive age during conception, to prevent neural tube defects in offspring.

In patients with repeated postoperative vomiting, thiamine (vitamin B1) deficiency may develop, leading to Wernicke syndrome, which must be urgently treated with parenteral thiamine administration.

All patients require postoperative follow-up and must receive adequate protein and multivitamin/mineral supplementation. Patients should avoid pregnancy for 12 months after restrictive gastric surgery and up to 18 months after malabsorptive procedures.

In addition to the bariatric surgeon, a bariatric team evaluates patients preoperatively and follows them throughout the entire postoperative period. The team may include a dietitian, bariatric nurse, endocrinologist-diabetologist, internist, pulmonologist, and psychiatrist/psychologist.

Conclusion

The use of medical therapy in severe obesity does not lead to sustained weight loss.

Thus, over the past 50 years, surgical procedures have been developed that ensure weight loss through gastric restriction with early satiety and, especially, through intestinal bypass with malabsorption.

Bypass operations are currently used to treat type 2 diabetes mellitus in patients with mild obesity.

Oral supplementation is required in the postoperative period, including vitamin D3, calcium, iron, vitamin B12, and folate.

MGB and OAGB procedures are performed relatively quickly and simply, with excellent resolution of comorbidities and sustained weight loss.