Brain responses to food and weight loss.

In this symposium report, we examine how functional neuroimaging has revolutionized the study of human eating behaviour. In the last 20 years, functional magnetic resonance and positron emission tomography techniques have enabled researchers to understand how the human brain regions that control homeostatic and hedonic eating respond to food in physiological and pathological states. Hypothalamic, brainstem, limbic and cortical brain areas form part of a well-co-ordinated brain system that responds to central and peripheral neuronal, hormonal and nutrient signals. Even in physiological conditions, it promotes the consumption of energy-dense food, because this is advantageous in evolutionary terms. Its function is dysregulated in the context of obesity so as to promote weight gain and resist weight loss. Pharmacological and bariatric surgical interventions might be more successful than lifestyle interventions in inducing weight loss and maintenance because, unlike dieting, they reduce not only hunger but also the reward value of food through their actions in homeostatic and hedonic brain regions. Functional neuroimaging is a research tool that cannot be used in isolation; its findings become meaningful and useful only when combined with data from direct measures of eating behaviour. The neuroimaging technology is continuously improving and is expected to contribute further to the in-depth understanding of the obesity phenotype and accelerate the development of more effective and safer treatments for the condition.