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Stanford Report, January 5, 2000

Researchers find teen dieting associated with weight gain and obesity


Teenage girls who diet are more likely to become obese than their non-dieting peers, according to a new Stanford study. Seemingly paradoxical, the findings jibe with research on adults and argue for a national weight education program, the researchers say.

Scientific research on the connection between dieting and weight loss has given conflicting results, possibly because many studies rely on the potentially biased testimony of dieters themselves. Some studies merely asked questions like, "Did you lose weight when you were on a diet?" and never put anyone on a scale. Moreover, few researchers have examined the relationship between dieting and weight during the teen years, when obesity often begins.

Led by Eric Stice, PhD, a Stanford postdoctoral fellow during the study and now an associate professor of psychology at the University of Texas, researchers tracked the weight and dieting habits of 692 teenage girls from 9th through 12th grade. Once a year, each girl had her weight and height measured and then filled out a general health questionnaire. Included among the questions were several asking whether the girl was currently dieting or exercising to lose weight, had ever used laxatives, vomiting or appetite suppressants to control weight, or had ever fasted or been a binge eater.

The study incorporated several precautions to encourage accurate answers. First, the researchers weighed the girls instead of accepting their reports of their own weight.

In addition, the study was blinded to prevent bias from coloring their answers -- the girls were told only that they were participating in a survey of behaviors and attitudes, not a study of weight control. In past dieting research where scientists revealed their aims, the pounds seemed to drop away -- and to stay off. But in the few blinded studies, dieting has proven ineffective or, even worse, seems to lead to weight gain.

As the researchers write in the December issue of the Journal of Consulting and Clinical Psychology, overall the girls gained weight steadily during the four years, at an average rate of about 3 pounds per year. The rate of obesity also rose from 16 percent to 21 percent.

Girls who had resorted to extreme weight-loss measures like laxatives and appetite suppressants were more likely to gain weight, as were those who had engaged in binge eating. Dieting, laxative and appetite suppressant use, and exercise for weight loss also greatly increased the likelihood of becoming obese, the analysis showed.

The results must be interpreted cautiously, says co-author Chris Hayward, MD, associate professor of psychiatry and behavioral sciences. "We are not saying dieting per se causes weight gain." Rather, Hayward explained, the analysis merely detected an association between weight gain and dieting that is not yet explained.

One possible explanation is that the girls may think they are dieting but aren't actually reducing their eating enough to make a difference. Another possibility is that the girls who resort to dieting or the more extreme weight loss methods are already prone to obesity -- for genetic or environmental reasons, Hayward said.

To discourage teens from trying extreme and unhealthy behaviors, Hayward and colleagues envision a national educational campaign along the lines of the successful public-health campaign against smoking.

Other Stanford authors on the paper include postdoctoral fellow Rebecca Cameron, PhD; professor of psychiatry and behavioral sciences C. Barr Taylor, MD; and associate professor of medicine Joel Killen, PhD.

Grants from the National Institutes of Mental Health, the National Institute for Child Health and Development, the Stanford Center on Adolescence, and the W.T. Grant Foundation supported the work. SR