Biopsychology of human appetite — understanding the excitatory and inhibitory mechanisms of homeostatic control

Human appetite is a biopsychological phenomenon that reflects the complex interaction of biological, psychological and environmental processes in the overall expression of food intake. As human appetite interacts with, and is affected by, energy expenditure, it is best viewed within an energy balance framework. Defining what drives and inhibits appetite is essential for the aetiology of overconsumption and obesity development in humans. The inhibitory control of appetite is thought to be achieved via an array of adipose and gastrointestinal derived peptides that modulate hunger and satiety on a meal-to-meal (episodic) and day-to-day (tonic) basis. To date, there has been much less attention on the biological origins of the drive to eat. Recent cross-sectional studies report positive associations between fat-free mass and resting metabolic rate with hunger, meal size and daily energy intake in weight stable individuals. These data have been interpreted to suggest that the metabolic activity of fat-free mass creates a functional drive to eat that ensures energy intake meets the basal energy requirements of vital tissues and organs. In this review we discuss the nature and extent of body weight regulation, what drives and inhibits human appetite, and the dynamic relationships between energy expenditure, body composition and energy intake during periods of energy balance and restriction.