Obesity

Obesity is caused by a variety of factors, all of which result in an excess of caloric intake relative to the body's expenditure of energy (calories) at rest, during activity, and, in childhood and adolescence, for growth. Calorie intake in excess of these needs is converted to fat. Less than 2 percent of obesity in childhood is due to endocrinologic conditions, such as thyroid disease. An equally small percentage is due to genetic disorders (e.g., the Prader-Willi Syndrome). Though obesity "runs in families," the genetic contributions to fatness are not well understood. A shared environment also contributes to the hereditary pattern of obesity, with parental influences on diet and exercise during childhood and adolescence. Numerous studies have failed to precisely define the relative contributions of caloric intake and expenditure to the development of obesity. The difference in daily intake necessary to result in as much as a ten-pound difference in weight gain over the course of a year is actually as little as a hundred calories per day. Studies have shown that more time spent using television, VCRs, and video games is associated with a greater likelihood of obesity and that decreasing the amount of time spent watching television correlates with less weight gain.

Some interesting developmental factors may contribute to overconsumption of calories. These include difficult infant or child temperament, poor self-regulation of intake, and an "obese eating style," involving rapid eating and rapid consumption of calories. Studies of infant feeding have revealed a style of vigorous feeding, similar to the obese eating style, with rapid sucking, at higher pressure, resulting in greater caloric intake at a feed. Studies of children's ability to self-regulate dietary intake have found poorer self-regulation of eating in fatter girls and in children exposed to a highly controlling parenting style. Studies of child temperament have found that difficult children (low in rhythmicity, approach, and adaptability; high in intensity; and negative in mood) show more rapid weight gain, perhaps as a result of being overfed by parents who use feeding as a soothing technique, and may later use eating as a technique for comforting themselves.