Understanding Psychology (10th Ed)

 THE ROOTS OF OBESITY 
Given that both biological and social factors infl uence eating behavior, determining 
the causes of obesity has proved to be a challenging task. Researchers have followed 
several paths. 
Some psychologists suggest that oversensitivity to external eating cues based on 
social factors, coupled with insensitivity to internal hunger cues, produce obesity. 
Others argue that overweight people have higher weight set points than other people 
do. Because their set points are unusually high, their attempts to lose weight by eat-
ing less may make them especially sensitive to external, food-related cues and there-
fore more apt to overeat and perpetuate their obesity (Tremblay, 2004; West, 
Harvey-Berino, & Raczynski, 2004). 
But why may some people’s weight set points be higher than those of others? 
One biological explanation is that obese individuals have a higher level of the 
hormone leptin, which appears to be designed, from an evolutionary standpoint, to 
“protect” the body against weight loss. The body’s weight-regulation system thus 
appears to be designed more to protect against losing weight than to protect against 
gaining it. Therefore, it’s easier to gain weight than to lose it (Ahiima & Osei, 2004; 
Zhang et al., 2005; Levin, 2006). 
Another biologically based explanation for obesity relates to fat cells in the body. 
Starting at birth, the body stores fat either by increasing the number of fat cells or 
by increasing the size of existing fat cells. Furthermore, any loss of weight past infancy 
does not decrease the number of fat cells; it only affects their size. Consequently, 
people are stuck with the number of fat cells they inherit from an early age, and the 
rate of weight gain during the fi rst 4 months of life is related to being overweight 
during later childhood (Stettler et al, 2005. 
According to the weight-set-point hypothesis, the presence of too many fat cells 
from earlier weight gain may result in the set point’s becoming “stuck” at a higher 
level than desirable. In such circumstances, losing weight becomes a diffi cult propo-
sition because one is constantly at odds with one’s own internal set point when 
dieting (Freedman, 1995; Leibel, Rosenbaum & Hirsch, 1995). 
Although obesity is reaching epidemic proportions in the United States, its exact causes 
remain unclear.