Acne fades and voices deepen, but teen obesity hangs around. U.S. Department of Agriculture researchers at Tufts University tracked weight and health patterns over the course of subjects’ lives. They found that whether or not people bring their weight under control during adulthood, having carried excess pounds during their teen years puts them at greater risk for certain cancers, circulatory problems, and mobility impairment in their elder years.

The study found that teen boys 20 pounds overweight were twice as likely as boys of normal weight to have died or contracted heart disease by the age of 70. Overweight girls were found not to be at higher risk of heart disease, but they were found to have great difficulty performing simple physical tasks during old age, and were at a higher risk of arthritis. Health risks were greatest for people remaining overweight from adolescence through adulthood.

Despite the findings, parents need not force their overweight teens into strict diets, advises Tufts researcher Aviva Must, Ph.D. They are unlikely to stick to them, which could make them feel like failures. And diets that bring quick weight loss may be detrimental to a growing teen’s health, says Must. Instead, she recommends a more subtle, long-term strategy: serving family meals relatively low in fat, limiting TV time, and encouraging vigorous exercise. Parents who set an example by adopting healthy habits for themselves will be most successful in helping their children.