What is the Mechanism Behind Weight Loss Maintenance with Gastric Bypass?

Abstract

Obesity is an epidemic on the rise. With the failure of non-surgical strategies, bariatric surgery has emerged as the most effective therapeutic option for the treatment of severe obesity. Among various surgical options, Roux-en-Y gastric bypass (RYGB) results in sustained weight loss and profound metabolic improvements. The traditional view that gastric bypass and bariatric surgery in general works primarily through restriction/malabsorption of nutrients has become obsolete. It is now increasingly recognised that its mechanisms of action are primarily physiologic, not mechanic. In fact, clinical and translational studies over the last decade have shown that a number of gastrointestinal mechanisms, including changes in gut hormones, neural signalling, intestinal flora, bile acid and lipid metabolism can play a significant role in the effects of this procedure on energy homeostasis. The clinical efficacy and mechanisms of action of RYGB provide a compelling evidence for the role of the gastrointestinal tract in the regulation of appetite and satiety, body weight and glucose metabolism. This review discusses the physiologic changes that occur after RYGB and that contribute to its mechanisms of action.

Body Weight Reduction and Biochemical Parameters of the Patients After RYGB and SG Bariatric Procedures in 12-Month Observation

“…However, body weight loss is most pronounced in the first 3 months after the procedure, and later, the weight reduction becomes slower. The factors contributing to the body mass loss during this period are radical reduction of consumed food, physiologically induced metabolic changes (bile acids), hormonal changes (fatty tissue, intestines) and modifications in nerve signalling and in intestinal microflora [4, 9]. The influence of neurohormones produced in small intestine becomes more pronounced, and the decrease in their levels leads to the reduction of insulin synthesis and insulin resistance of the tissues [21].…”

Vertical sleeve gastrectomy activates GPBAR‐1/TGR5 to sustain weight loss, improve fatty liver, and remit insulin resistance in mice

“…Bariatric surgery has emerged as an attractive clinical intervention given its ability to achieve greater and more sustainable weight loss than those observed with lifestyle changes or pharmacological therapy . To date, Roux‐en‐Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) represent the two most commonly performed bariatric surgeries; both surgical interventions induce significant weight loss and improve glucose tolerance in humans and rodent models .…”

“…Additionally, BAs also serve as hormones that alter metabolism by targeting the nuclear farnesoid X receptor (FXR, NR1H4) and the cell membrane‐associated G protein‐coupled BA receptor 1 (GPBAR‐1, MBAR1, hereafter referred to as TGR5) . Many studies have described the clinical impact on BA circuitry following RYGB and VSG . In general, surgical changes to the gastrointestinal anatomy increase BA absorption by both the ileum (the distal part of the small intestine) and the liver.…”

Diarrhea after bariatric procedures: Diagnosis and therapy

“…SG, however, was shown to cause a change in the Bacteroidetes/Firmicutes ratio, indeed, with a distinct increase in Bacteroidetes and a decline in the abundance of Firmicutes[68]. While the exact mechanisms remain unclear, change of the individual’s microbiota composition is considered to be a key factor of postoperative body weight reduction and may be one of the potential contributors to a stable weight loss after bariatric surgery[65,69]. Even though one would assume the importance of the microbiome regarding occurrence and/or resolution of diarrhea after bariatric surgery, this has not yet been elucidated.…”