This is the 2007 version. Click here for the 2017 chapter 09 table of contents.

Factors Influencing Fat Deposition

What factors influence a person's ultimate weight? Twin studies indicate that genes account for about 80% of the expected variation in a person's adult weight. However, this does not mean that calories do not count, because the genetic influence is probably expressed in satiety variation (how easily a person feels full and stops eating). The genetic influence explains why identical twins usually weigh about the same and put on weight at the same periods in their lives, even if they have been reared apart since birth. Children who are adopted end up with a body mass that correlates with their biological parents, not their adoptive parents (Bray & York, 1979).

What is evidence for genetic influences on fatness?

Over half of obese humans admit to binges of eating. Binge eating stimulates formation of more fat cells. The two main causes of obesity—genetics and overeating—can be distinguished in laboratory animals by testing for abnormal secretions of adipsin, a chemical produced by fat cells. Genetic disorders that produce obesity are marked by abnormalities in adipsin release.

What does research suggest about the effect of exercise on weight loss?

Does exercise help dieters? For the average college student, the answer is probably yes. However, exercise is difficult for people who are extremely obese. Those people have a low capacity for strenuous exercise. As one expert noted, "If you are obese enough to need to exercise in order to lose weight, you probably won't be able to exercise enough to boost your body's metabolism" (Kolata, 1987). Even in non-obese people, evidence for an effect of exercise on weight loss is surprisingly thin. While exercise does burn calories, successful dieters do not seem to require exercise as a condition for losing weight. Dieters succeed just as often without it.

What does research show about fidgeting?

Exercise of the workout variety may not be as important as constant, smaller scale activity. Studies indicate that fidgets—-small movements people make without thinking about it—consume more energy than planned exercise programs. Technically, fidgeting is called "nonexercise activity thermogenesis" (NEAT). Research indicates that when most people overeat, "activation of NEAT dissipates excess energy" (Levine, Eberhardt, & Jensen, 1999). That explains why some people eat high-calorie meals without gaining weight. People who become obese often have a lower NEAT level, making it harder for them to burn off excess calories.

What does Hirsch recommend to people who are "born fat"?

Jules Hirsch of Rockefeller University is a proponent of the theory that "People are born fat." He recommended a moderate amount of dieting and a moderate amount of exercise. "My chief advice is that people be aware of what they are eating and making changes, however small, that they can stay with forever" (Kolata, 1988). He also recommended that obese people increase their daily exercise in regular, unobtrusive ways, such as taking stairs instead of elevators or "parking their car farther from their homes or offices and walking the extra distance."


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