Biopsychology Of Motivation

Hunger and Eating

Many theories of hunger are historically discussed from the biological component. Cannon and Washburn (as cited in Coon, 1995) came up with the stomach contraction theory which states that we know we are hungry when our stomach contracts. In the notorious balloon study, Washburn trained himself to swallow a balloon which was attached to a tube, then the balloon was inflated inside of his stomach. When the balloon was inflated, he did not feel hungry. Later this theory was opposed by the fact that people whose stomach was removed still felt hungry. Glucose theory states that we feel hungry when our blood glucose level is low. Bash (as cited in Franken, 1994) conducted an experiment transfusing blood from a satiated dog to a starved dog. The transfusion resulted in termination of stomach contraction in the starved dog, and supported the glucose theory. But as LeMagnen (as cited in Kalat, 1995) suggests that blood glucose level does not change much under normal conditions. Insulin theory states that we feel hungry when our insulin level increases suddenly in our bodies (Heller, & Heller, 1991). However, this theory seems to indicate that we have to eat to increase our insulin level in order to feel hungry. Fatty acid theory states that our bodies have receptors that detect an increase in the level of fatty acid. Activation of the receptor for fatty acid triggers hunger (Dole, 1956, Klein et al., 1960 cited in Franken, 1994). Heat-Production theory suggested by Brobeck (as cited in Franken, 1994) states that we feel hungry when our body temperature drops, and when it rises, the hunger decreases. This might be explain that we tend to eat more during winter.

Health

Many theories point out that obese people have a strong biological component of hunger and eating. What about people with eating disorders? What is the mechanism of hunger and eating for people with eating disorders? There are mainly three kinds of eating disorders; Binge Eating, Anorexia Nervosa, and Bulimia. Binge eating is characterized by one's eating a very large amount of food until she or he feels uncomfortably full. This binge eating is done when one is not hungry. According to the DSM-VI, Anorexia Nervosa has two types; restricting type, and binge-eating/purging type (American Psychiatric Association, 1994). Anorexia Nervosa restricting type is when one extremely restricts food intake, and it is not followed by binge-eating or purging behavior. On the other hand, Anorexia Nervosa binge-eating/purging type was described as one engaged in purging and binge-eating regularly. A common symptom of Anorexia is one's putting her or himself on self-starvation to avoid feeling fat or gaining weight. Although people with this disorder weigh far below normal, they still think they are overweight. Eventually they are at risk of losing their lives due to malnutrition.

People with this disorder still feel hungry, yet they cannot eat because they are too afraid of gaining weight. Physiological causes of this disease are not yet clear, although there are some findings showing a connection with serotonin and norepinephrine. The learned component of Anorexia cannot be ignored. Studies show that there is more Anorexia in westernized cultures than other cultures, (e.g., Suematsu, 1986), because the social value of slimness pushes people to be thinner. Cognitively, these people have a distorted body image of themselves, and dissatisfaction with their own body image, which is influenced by the cultural value of slimness, and leads to eating disorders (Mumford, Whitehouse, & Choudry, 1992).

Bulimia Nervosa is a condition of binge eating followed by purging and use of laxatives (American Psychiatric Association, 1994). Unlike Anorexia, people with this disorder are normal or above weight. Psychologically, having quilt and shame are common symptoms among people with Bulimia. Unlike anorexic people who put absolute control over restricted eating, bulimic people cannot control their eating. The physiological cause of Bulimia is still unclear. Psychologically, Bulimia is said to be linked to depression and anxiety, but clear evidence of causation has not yet been found. Cognitively, people with Bulimia are said to be motivated to escape from reality by binging. It is possible that those people were given food by their caretakers to lift their mood in their childhood. Like Anorexia, cultural learning that one needs to be thin to be accepted may also contribute to the cause.

Reference:

http://www.csun.edu/~vcpsy00h/students/hunger.htm