Study: teens who try fad diets gain more weight over time

Researchers at the University of Minnesota followed local students over a decade and found that those who tried risky diets in their adolescent and teen years were more likely to gain more weight by their twenties.

Their findings, reported in the latest Journal of Adolescent Health, show that students who tried weight-loss solutions such as skipping meals or diet pills in 1999 and 2004 were likely to be heavier in 2009. Girls who tried these weight loss tactics gained 4.63 points in their body mass indexes over the 10-year study. (BMI is a measure of body fat based on height and weight. A one-point increase equates to roughly five pounds of excess weight gain.) Girls who didn't try these diets only gained 2.29 points on their BMIs.

The findings held up regardless of whether the students from Minneapolis, St. Paul and Osseo were overweight at the start of the study. This was an important nuance to the study. After all, it's logical that overweight kids would be more likely to (a) try extreme dieting, and also (b) end up with proportionately more weight gain than slimmer peers.

The study doesn't address the "why" question, but lead author Dianne Neumark-Sztainer has a theory on why the dieters gained more weight: "It's probably that these (risky dieting) behaviors are being substituted for healthy behaviors. They're probably going on and off and on and off these behaviors as opposed to implementing an ongoing routine of healthier eating and physical activity."

The greatest increases in BMI were noticed among students who attempted skipping meals or eating very little, girls who tried diet pills, and boys who sought to replace food with alternatives such as powders and special drinks.

"We really want to help kids stay away from this sort of short-term dieting," Neumark-Sztainer said, "and the use of unhealthy weight control behaviors."

An inherit problem in this type of research is that findings often come out years after the studies were completed. Some of the "children" in this study now have their own children. But Neumark-Sztainer said she will be publishing additional research shortly showing that today's teens face the same pressures and temptations to diet as teens from a decade earlier. Also, she said she is applying for a grant to continue to follow this initial group of students into their adulthood.