89 Hunger and Eating
Learning Objectives
By the end of this section, you will be able to:
- Describe how hunger and eating are regulated
- Understand the role of the hypothalamus in hunger and eating
- Explain the health consequences resulting from anorexia and bulimia nervosa
Eating is essential for survival, and it is no surprise that a drive like hunger exists to ensure that we seek out sustenance. While this chapter will focus primarily on the physiological mechanisms that regulate hunger and eating, powerful social, cultural, and economic influences also play important roles. This section will explain the regulation of hunger, eating, and body weight, and we will discuss the adverse consequences of disordered eating.
Physiological Mechanisms of Hunger and Eating
There are a number of physiological mechanisms that serve as the basis for hunger. When our stomachs are empty, they contract. Typically, a person then experiences hunger pangs. Chemical messages travel to the brain, and serve as a signal to initiate feeding behaviour. When our blood glucose levels drop, the pancreas and liver generate a number of chemical signals that induce hunger (Konturek et al., 2003; Novin, Robinson, Culbreth, & Tordoff, 1985) and thus initiate feeding behaviour.
For most people, once they have eaten, they feel satiation, or fullness and satisfaction, and their eating behaviour stops. Like the initiation of eating, satiation is also regulated by several physiological mechanisms. The food’s passage through the gastrointestinal tract also provides important satiety signals to the brain (Woods, 2004), and fat cells release leptin, a satiety hormone.
The various hunger and satiety signals that are involved in the regulation of eating are integrated in the brain. Research suggests that several areas of the hypothalamus and hindbrain are especially important sites where this integration occurs (Ahima & Antwi, 2008; Woods & D’Alessio, 2008). Ultimately, activity in the brain determines whether or not we engage in feeding behaviour (Figure EM.12).
The Hypothalamus
The hypothalamus (located in the lower, central part of the brain) plays a very important role in eating behaviour. It is responsible for synthesizing and secreting various hormones. The lateral hypothalamus (LH) is concerned largely with hunger and, in fact, lesions (i.e., damage) of the LH can eliminate the desire for eating entirely—to the point that animals starve themselves to death unless kept alive by force feeding (Anand & Brobeck, 1951). Additionally, artificially stimulating the LH, using electrical currents, can generate eating behaviour if food is available (Andersson, 1951).
Hunger is only part of the story of when and why we eat. A related process, satiation, refers to the decline of hunger and the eventual termination of eating behaviour. Whereas the feeling of hunger gets you to start eating, the feeling of satiation gets you to stop. Perhaps surprisingly, hunger and satiation are two distinc