Bariatric surgery is an effective intervention for obesity and its metabolic consequences but its mechanism of action is poorly understood, particularly why positive metabolic effects are observed before (or independently of) weight loss. This may be a result of the surgery itself, or a consequence of the marked caloric restriction that follows. The clinical use of bariatric surgery provides an excellent opportunity to use it as a model to understand the mechanisms of the adverse physiological effects of obesity. The use of bariatric surgery as an experimental tool will provide important insights into gut-brain interactions, linking priorities in mechanistic and neuroendocrine research. Suggested developments include: