Hunger

Hunger is a specific and compelling sensation, sometimes arising from internal signals of nutrient depletion but more often modulated by numerous environmental variables including taste or palatability and ease or cost of procurement. Hunger motivates appetitive or foraging behaviors to find food followed by appropriate proximate or consummatory behaviors to eat it. A critical concept underlying food intake is the flux of chemical energy through an organism. This starts with inputs of food with particular energy content, storage of excess energy as adipose tissue or glycogen, and finally energy expenditure as resting metabolic rate (RMR) or as metabolic rate is modified by physical activity. These concepts are relevant within the context of adequate theoretical accounts based in energy homeostasis; historically, these are mainly static models, although it is now clear that these do not address practical issues such as weight gain through life. Eating is essentially an episodic behavior, often clustered as meals, and this has led to the idea that the meal is a central theoretical concept, but demonstrations that meal patterns are greatly influenced by the environment present a challenge to this tenet. Patterns of eating acquired during infancy and early life may also play a role in establishing adult norms. Direct controls of feeding are those that emphasize food itself as generating internal signals to modify or terminate an ongoing bout of eating, and include a variety of enteroendocrine hormones and brainstem mechanisms. Additionally, many studies point to the essential rewarding or hedonic aspects of food intake, including palatability, and this may involve integrative mechanisms in the forebrain and cerebral cortex.