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.