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Research shows dieting without
exercise can slow kids' growth
February 2, 1998

When overweight adults seek to slim down, the prescription is pretty simple: decrease calories, or in more technical terms, create a "caloric deficit." This is often done through diet, exercise, or both, and if the participants are successful, pounds are lost. So when faced with overweight children, parents, doctors, and others tend to recommend the same formula. Recent research at UConn shows that this may not be the best approach.

"Children are still growing," says Nancy Rodriguez. "Creating a caloric deficit can negatively affect the way children process protein, which in turn could slow or even compromise their growth."

This presents the question: can overweight children lose weight without slowing their natural growth process.

Nancy Rodriquez, right, speaks with sports nutrition major Laura Hanley after clas.

Photo by Peter Morenus

The topic became the focus of a study that Rodriguez, an associate professor of nutritional science, undertook in 1995. Underwritten by a grant from the American Heart Association, the study allowed Rodriguez and then-doctoral student Cara Ebbeling, an exercise physiologist, to examine more closely how cutting calories and increasing activity would affect body composition and the use of protein in overweight children between the ages of 8 and 10 years. Their findings indicate that caution should be exercised before putting a child on a diet.

"We found that diets should be combined with exercise, because dieting alone significantly slowed protein turnover, the way that protein is processed and used by the body," Rodriguez says. "If you slow this process down, then you may be hindering a child's growth."

Protein turnover key to formula
The 12-week study Rodriguez and Ebbeling created was financed in part by a grant from the American Heart Association. The participants were overweight children 8 to 10 years old. Twenty-five were identified and enrolled in the study, 15 girls and 10 boys, representing a variety of ethnic groups.

During the study's first two weeks participants were asked not to change their eating habits and activity (or lack of activity) rates. Food intake and activity were charted, as were baseline body composition measurements and protein turnover rates.

Rodriguez and Ebbling also met individually with the children to talk about eating habits and create a more balanced meal plan for each participant. This didn't mean starving or even skimping on meals. But the kids would have to deal with less of some foods - often the fattier items - and more of other foods such as fruits and vegetables.

"Of course we had kids that hated vegetables, but we didn't encounter any that hated fruits and vegetables," Rodriguez says. "In their diets, fruit replaced vegetables. There were others who would only eat one kind of vegetable, be it beans or corn or carrots. So we said to the parents, "Fine, carrots every night." If the child likes them and eats them, then it's better than a kid using cookies to supply those calories."

After the two-week baseline period, the participants switched to meal plans that reduced their intake by about 500 calories per day. In the final six weeks, a sub-sample of the children were asked to continue with the reduced calorie diets, but also to walk for half an hour five days per week. This created an added caloric deficit of between 100 and 300 calories per walk. Throughout the study, protein turnover rates were monitored.

Some of the children dropped out of the study after only a few weeks for lack of support at home.

Another problem arose during the "walking" phase of the study when some parents began dropping off the kids every day.

"I had to remind (the parents) that part of this study was about building support systems and creating behaviors that reinforce good diet and exercise habits," says Rodrigue.

Of the 25 children enrolled, 16 completed the study.

Moderation in all things
The data generated by the study indicated that protein turnover began to slow dramatically during the diet-only phase of the program, even though the children's calories were being cut only moderately. However, the children who had regular walking added to their diets soon had their turnover rates return to near baseline levels.

"There was something about this regular physical activity that stimulated more efficient protein turnover," Rodriguez says. "The data indicated that a stand-alone diet, even a moderate one, needs to be combined with regular activity to be safe for children."

Rodriguez says both the diets and exercise should remain moderate. "The kids put this weight on a couple of pounds a week and that's the only safe way to take it off."

The study has paved the way for Rodriguez to receive a grant from the USDA to initiate further examination of protein usage in healthy children and the effects of physical activity.

"Odd as it may seem, there's been very little data gathered on this," she says. "The current USDA protein recommendations for children are based on extrapolations generated from figures we have on adults and infants. So doing more work in this area is important, and I'm very excited to see what we find."

David Pesci