Neurobiology of food intake in health and disease

Under normal conditions, food intake and energy expenditure are balanced by a homeostatic system that maintains stability of body fat content over time. However, this homeostatic system can be overridden by the activation of 'emergency response circuits' that mediate feeding responses to emergent or stressful stimuli. Inhibition of these circuits is therefore permissive for normal energy homeostasis to occur, and their chronic activation can cause profound, even life-threatening, changes in body fat mass. This Review highlights how the interplay between homeostatic and emergency feeding circuits influences the biologically defended level of body weight under physiological and pathophysiological conditions.