Episodic Events Hunger Satiety and the Appetite Cascade

A good place to start is the psychological experiences of hunger and satiety that underpin the pattern of eating behavior. Hunger can be defined as the motivation to seek and consume food initiating a period of feeding behavior. The process that brings this period to an end is termed satiation. Satiation processes ultimately lead to the state of satiety in which the hunger drive, and consequently eating behavior, is inhibited. The processes of satiation determine the meal size and the state of satiety determines the length of the post meal interval. The net effect of these systems can be considered before (preprandial or cephalic phase), during (prandial), and after (postprandial) a meal (see Figure 1).

Preconsumption physiological signals are generated by the sight and smell of the food, preparing the body for ingestion. Such afferent sensory information, carried to the brainstem via cranial nerves, stimulates hunger before eating and during the initial stages of consumption (the prandial phase). During the prandial phase the CNS receives postin-gestive sensory afferent input from the gut reflecting both the amount of food eaten and earliest representations of its nutrient content. Mechanoreceptors in the gut detect the distension of gut lining caused by the presence of food aiding the estimation of the volume of food consumed. Gut chemoreceptors detect the chemical presence of various nutrients in the gastrointestinal tract providing information on the composition (and possible energy content) of the food consumed. Prandial and postprandial signals are generated by the detection of nutrients that

Daily pattern of eating behavior

Daily pattern of eating behavior

Meal

Meal

Meal

Meal

Meal

Figure 1 The satiety cascade. The signals generated prior to (preprandial), during (prandial), and after (postprandial) the consumption of a meal critical to short-term (episodic) meal-by-meal appetite regulation throughout the day.

have been absorbed from the gastrointestinal tract and have entered the circulation in the periphery (postabsorptive satiety signals). Circulating nutrients that are either metabolized in the periphery (e.g., liver) activate central nervous system (CNS) receptors (e.g., in brainstem), or they enter and affect the brain directly and act as postabsorptive metabolic satiety signals.

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