Gastrointestinal hormones, energy balance and bariatric surgery

Abstract

Despite increasing understanding of the changes in gastrointestinal and central neuroendocrine signaling following gastric bypass surgery (GBP) in morbidly obese patients, the mechanisms underlying weight loss and weight loss maintenance are not completely understood. Changes in energy expenditure are increasingly recognized as an important factor contributing to weight loss and metabolic effects in patients following GBP surgery. Experimental data regarding changes in energy balance following metabolic surgery in animal models suggest increased energy expenditure postoperatively as an important factor in the process of weight loss. However, the underlying neuroendocrine mechanisms are not well understood, and data regarding changes in energy expenditure in humans after GBP are inconsistent because of heterogenic patient populations and variable techniques. Nevertheless, a growing body of knowledge and understanding of the complex entero-neurohumoral interaction with its consequences in appetite, satiety and energy expenditure will help reveal the mechanisms of weight loss and weight loss maintenance following GBP surgery. Here we review how gastrointestinal hormones potentially regulate energy balance, and summarize current available experimental and clinical data on energy expenditure following obesity surgery.

Alcohol Reward Is Increased after Roux-en-Y Gastric Bypass in Dietary Obese Rats with Differential Effects following Ghrelin Antagonism

“…Following RYGB, patients typically lose approximately 30% of total body weight or 60–70% of excess body weight [3]. Although the exact mechanism remains unknown, it is believed that factors other than restriction and malabsorbtion of the ingested food may contribute to the beneficial effects of RYGB surgery [4], [5]. Following RYGB, patients voluntarily restrict consumption of calorie-dense, highly palatable foods such as fats, concentrated carbohydrates, ice cream, and sweetened beverages [6], [7], [8], [9].…”

Mechanistic Comparison between Gastric Bypass vs. Duodenal Switch with Sleeve Gastrectomy in Rat Models

“…The increased resting energy expenditure in the animal models after GB is in accordance with some, but not all, reports in humans. The discrepancies in the clinical studies may include the heterogeneity of patient populations and measurements of energy expenditure for a limited time using portable metabolic carts under artificial rather than “free-living” conditions [35]. Nerveless, resting energy expenditure has been suggested to be a therapeutic target for obesity [32], [36].…”

Mechanisms of Bariatric Surgery

“…Chronic caloric deprivation is normally accompanied by a decrease in resting energy expenditure as the body strives to conserve energy [ 42 ]. These are some inconsistencies as to what happens to resting energy expenditure after bariatric surgery, but the majority of human and/or animal studies have shown that it remains stable on decreases after RYGB, VSG and AGB [ 21 , 43 -52 ].…”