Demonstration
Hunger: The Story Continues
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Clearly, glucose level plays a role in determining when and how much we eat. However, although the glucose set-point theory explains hunger over short periods of time, the glucose level fluctuates too much to explain why healthy adults are able to keep their weight relatively constant over months and years. To address this issue, another theory suggests that long-term weight regulation is controlled by the amount of body fat. In the next section, we'll explore this "body fat set-point theory."
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Body Fat Set-Point Theory
Evidence that long-term eating behavior is regulated in a way to maintain a set point of body fat comes from studies of normal-weight individuals. In these individuals, about 15 percent of body weight is fat in adipose tissue, enough to meet the body's calorie needs for about a month. When this target level is exceeded, normal-weight people generally eat less until the level drops back to 15 percent. When fat stores drop below this level, normal-weight people generally show lower body metabolism and higher food consumption until the fat stores are replenished.
Set-Point Theories Combined
By combining body fat and glucose set-point theories, researchers thought that they had successfully explained eating behavior: Short-term eating behavior is regulated by glucose level, while long-term eating behavior is regulated by the amount of body fat.Complicating Factors
Once again, the issue turned out to be more complicated. If human eating behavior really is controlled by a glucose set point and a body fat set point, then why do so many people eat more than they need to maintain a constant level of glucose and body fat? People who have been snacking before a meal already have high glucose levels before they sit down to eat, and yet they probably will eat a normal sized meal. Roughly a third of the people in the United States have a far larger amount of stored fat than they need, and yet they continue to consume excess calories. Set-point theory predicts that their hunger should diminish, allowing their body fat to return to its original level, but instead they continue to gain weight and add body fat.To understand why people eat more than their bodies need, we must consider some additional psychological factors.