Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 09 table of contents.
One idea from Hull's theory remains very current. That is the idea that biological motives resemble control systems or regulatory systems in the body. Research has shown that biological motives like hunger and thirst do indeed operate as homeostatic systems, regulating basic biological variables. Weight control, for example, is related to energy regulation in the body.
Which idea from Hull's theory remains current?
Keeley and colleagues coined the term set-point to refer to the level of fat in the body that is kept at a certain level (Keeley & Powley, 1986). Fat cells are elastic. If animals are given access to adequate supplies of food and left alone, the fat cells stay constant in size. This indicates some sort of regulatory process.
What does it mean to say the body "defends" the set-point?
Why is fat regulated so closely? Fat is the most energy-dense substance in the body. By regulating levels of fat, the body regulates storage of reserve energy. The natural or ideal level of fat in your body is the set-point. The concept of a set-point is particularly reminiscent of Hull's assumption that motivation is homeostatic—aimed at maintaining a crucial variable within an ideal range. The set-point determines what level of fat the body will return to, other things being equal.
A dieter does not lose fat cells; rather, each fat cell shrinks. When the fat cells get small enough, the organism takes action to restore fat levels to the set-point. That is what it means to say the organism defends the set-point.
The following compensations occur when fat levels fall below the set-point, as part of the organism's active defense of the set-point:
1. The basal metabolic rate or BMR, the background level of energy consumption in the body, is reduced. Body heat is lowered.
2. More calories are extracted from food as it is digested; fewer calories are excreted in waste products.
3. Activity level, except for that directed at food, decreases to conserve energy.
These changes make it harder to lose weight when one is below the set-point...and easier to regain weight after a diet. The body acts as though it wants to restore the level of fat to the set-point. That is why many people regain the weight they have lost during a successful diet.
What happens when a person who is "naturally skinny" eats a rich meal?
Some people generate low numbers of fat cells. They are naturally thin. They find it difficult to gain weight no matter how much they eat. The more calories they consume, the more efficiently their bodies burn off the excess calories. Thus they "defend" their low weight. This energy burn-off takes the form of metabolic adjustments that are the opposite of those listed above. After a big meal, the naturally thin person will experience the following compensations:
1. Basal metabolic rate and body heat rise as the body's cellular engines are turned up a notch and extra calories are burned off.
2. Less energy will be absorbed from food, as the body cuts back on insulin, which converts food to energy.
3. Activity levels and fidgeting increase after a brief rest.
Most people do not consider natural thinness to be a problem. Fatness is more of a worry. A person with a high set-point can lose weight but usually will put it right back on, if he or she resumes previous eating patterns. To make matters worse, each rebound from dieting tends to raise the set-point a little bit.
How can weight be lost, despite the influence of the set-point?
So is dieting hopeless? Not entirely. The existence of a storage system for fat does not mean fat levels are permanently fixed and cannot change. The opposite is true. To be useful, the fat must be accessible. Fat is like money in a bank account. It is only helpful if you can get it out when you need it; otherwise there is no point in storing it. How does one withdraw fat from the fat bank? Create conditions in which the body must draw upon its energy supplies. There are three options: take in fewer calories, increase energy consumption by exercising, or do both.
What do "sophisticated" diet programs emphasize? Why?
To maintain a low weight without the rebound to a higher weight, the change in dietary patterns must be permanent. This is why sophisticated diets emphasize a change of lifestyle rather than a temporary change of diet. Some weight-loss programs refuse to use the word "diet" at all, because it implies a temporary change. They work with a philosophy more like alcoholism treatment programs. One is encouraged to give up old ways and adopt a new way of living.
For some people trying to lose weight, overeating is like an addiction. Like some drug addicts, some overweight people succeed in changing their lives and altering their behavior patterns without a dramatic intervention like surgery. However, eating is different from other addictions in one crucial respect: nobody can abstain from eating completely. So temptation is constant, and recidivism (backsliding) is common. Statistics show 90% of diets are failures, if success is defined as permanent weight loss.
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