Many adolescent girls try to control their weight in ways that may leave them deficient in calcium, iron and other essential nutrients, a new study suggests.

The study of more than 4,100 students at Minnesota middle schools and high schools found that 57 percent of girls were using at least one unhealthy approach to weight loss, such as fasting, skipping meals, smoking, or using laxatives, diet pills or diuretics.

What’s more, compared with their peers who weren’t trying to control their weight, girls who were ate fewer fruits, vegetables and grains, and had lower intakes of calcium, iron and several vitamins. In general, the girls had poorer diets compared with girls who weren’t trying to control their weight and those who were using healthy means, such as increasing fruit and vegetable intake, cutting down on sweets, and exercising.

The results are published in the June issue of the Journal of the American Dietetic Association.

“I think that the findings are very concerning,” Dr. Dianne Neumark-Sztainer, the study’s lead author, said in an interview.

It’s true that the U.S. is facing an obesity problem, she noted, but “diets,” like the ones many of the girls in this study turned to, are not the answer.

Instead, children and teens, like adults, need to learn to follow a healthy lifestyle that includes regular exercise and plenty of fruits, vegetables and low-fat dairy products, according to Neumark-Sztainer, an associate professor at the University of Minnesota School of Public Health in Minneapolis.

And one key way for them to learn that, she said, is for parents to eat well and exercise themselves.

“If you have a child who is overweight,” Neumark-Sztainer added, “you don’t need to tell them that - they know.”

Rather, she said, parents need to support the child by buying healthful foods and encouraging physical activity. She also pointed out that, though it may seem like it will go in one ear and out the other, telling kids that they need nutrients like calcium and iron for long-term health may also help,

The study included 4,144 public school students who answered questions on their diets and whether they used any number of weight-control tactics, some healthy, some not.

A large majority of girls - nearly 88 percent - said they were trying to lose or maintain their weight, more often than not by unhealthy means. The fact that so many girls were worried about their weight is another concerning finding, Neumark-Sztainer said, because most were not overweight, and it’s clear that “body dissatisfaction” was playing a big role.

The findings for boys painted a much more puzzling picture. Nearly one third said they’d tried to control their weight in an unhealthy manner, but these boys did not show the nutritional consequences that girls did. In fact, they had the highest fruit intake of all the boys in the study.

In general, boys trying to control their weight, whether through healthy or unhealthy means, had higher-quality diets.

Neumark-Sztainer said the findings for boys are difficult to explain, and noted that the overall body of research on boys’ nutrition has often yielded data that “don’t make a lot of sense.”

It’s possible, she speculated, that boys who have tried unhealthy approaches to weight loss often give healthy tactics a shot as well - or that when boys use an unwise approach like fasting, it doesn’t turn into a long-term habit.

SOURCE: Journal of the American Dietetic Association, June 2004.