Gastric Bypass for Obesity: Mechanisms of Weight Loss and Diabetes Resolution

Energy homeostasis and medical vs. surgical methods to overcome it Obesity is now a global pandemic that continues to accelerate despite the often Herculean efforts by afflicted individuals to lose weight. These efforts are thwarted by a physiological system that regulates body weight in a manner analogous to that by which a thermostat controls ambient temperature. For each individual, there is a highly genetically influenced level of adiposity that is defended by this adipostatic control system, wherein alterations in body fat stores trigger compensatory changes in appetite and energy expenditure that resist weight change (1). It is hypothesized that these processes evolved to defend against malnutrition in times of famine, and hence, the adaptive responses to weight loss appear to be more robust than are those to weight gain (as any dieter can attest). Because of this body weight regulation system, known as energy homeostasis, nonsurgical methods are notoriously ineffective at achieving major, long-term weight reduction. In general, no more than 5–10% of body weight is lost through dieting, exercise, and the few available antiobesity medications, and recidivism after di