Two factors drive our desire to eat: hunger and appetite (Fig. 10-6). Hunger, the physiological drive to find and eat food, is controlled primarily by internal body mechanisms, such as organs, hormones, hormonelike factors, and the nervous system.11 Appetite, the psychological drive to eat, is affected mostly by external factors that encourage us to eat, such as social custom, time of day, mood (e.g., feeling sad or happy), memories of pleasant tastes, and the sight of a tempting dessert.
Internal and external signals that drive hunger and appetite generally operate simultaneously and lead us to decide whether to reject or eat a food...Although hunger and appetite are closely intertwined, they don’t always coincide. Almost everyone has encountered a mouthwatering dessert and devoured it, even on a full stomach. Alternately, there are times when we are hungry but have no appetite for the food being served. Where food is ample, appetite—not hunger—mostly triggers eating.
Fulfilling either or both drives by eating sufficient food normally brings a state of satiety, in which we feel satisfaction and no longer have the drive to eat. The hypothalamus, a portion of the brain, is the key integration site for the regulation of satiety (Fig. 10-7)...If these internal signals stimulate the satiety centers of the hypothalamus, we stop eating. If they stimulate the feeding centers in the hypothalamus, we eat more.11 Surgery and some cancers and chemicals can harm the hypothalamus. Damage to the satiety center causes humans to become obese, whereas damage to the feeding center inhibits eating and eventually leads to weight loss.
