The set point theory of weight control also reflects the role of genetics. Proponents of this theory suggest that the body works to maintain a certain weight. More specifically, each person has an internal set point for fatness, sometimes called the a dipostat, that the body seems to regulate by adjusting hunger, appetite, food intake, and energy expenditure. Researchers have demonstrated that human and animal subjects who have been put on low calorie or highcalorie diets lose and gain only to a certain level. When the diet ends, food consumption increases and they return to their approximate original weight.
How the body determines its set point is not known. One hypothesis is that the body is able to adjust its energy expenditure by varying how efficiently muscles burn calories. Researchers at New York’s Rockefeller University discovered that a dieter’s metabolism slows down after losing weight, so that doing the same amount of exercise at the new weight burns fewer calories. The researchers found that after losing 10% of their body weight, newly slimmer patients expended 15% less energy than expected for someone of similar size and body composition. The system also works in the other direction; when patients gained weight, their metabolism increased 16%. After a quick weight gain, the metabolism speeds up to make muscle activity burn more calories, quickly bringing the body back to its normal weight-its set point. Whatever direction a person’s weight goes, up or down, losing weight or gaining weight, the body tends to resist that change.
Can a person change his or her set point? Proponents of the set point theory think that the set point does shift over time in response to behavioral factors: eating a high-fat diet tends to raise the set point for fatness and regular physical activity tends to lower it. This shift may be so slight and gradual as to go unnoticed for years.
Some proponents of the set point theory suggest that because some people are genetically programmed to have unwanted pounds, efforts to eliminate fat with diet, exercise, or both are doomed. The body can shut down its calorie-losing mechanism by lowering metabolism and can stimulate appetite to the point that a person must have food.
Other proponents of the set point theory argue that vigorous regular exercise lowers the set point and thereby lowers the level of fat the body will accept and defend. Exercise induces the body to stabilize at a lower body weight, which is precisely what dieters are trying to do. Unfortunately there is no formula for calculating that a specific amount of exercise will result in the loss of a certain number of pounds. Individual response to exercise varies in ways similar to the differences in response to dieting. Still, exercise seems to be the best way to over power the body’s set point. This is a classic case of a genetic inclination being modified through appropriate lifestyle behavior. It supports the idea that heredity (that is, obesity) is not destiny. Living a healthy life-through regular exercise and sound nutritional habits cannot negate heredity, but it can modify it.
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