Dairy, moderate fat, carbohydrate intakes reduce obesity in young teens

02/24/04

American Heart Association meeting report

SAN FRANCISCO, March 4 Children who ate few dairy products and had low or high intakes of dietary fat gained more weight than those on a moderate fat diet, according to a study presented today at the American Heart Association's 44th annual Conference on Cardiovascular Disease Epidemiology and Prevention.

"The rise in obesity in the nation's young people may be partly due to fewer home-cooked meals, more calorie-dense foods, and more takeout and prepackaged dinners," said Lynn L. Moore, D.Sc., associate professor of medicine at Boston University School of Medicine. "There has also been a shift toward higher intake of sodas, rather than milk.

"Some of the dietary trends of the past couple of decades may have contributed to reduced intake of beneficial foods, such as dairy products. Adolescent girls, in particular, have reduced their consumption of dairy products, in part due to fear of gaining weight. If weight gain is a concern, reduced-fat dairy products may be substituted for full-fat products."

As part of the Framingham Children's Study (FCS), Moore and her colleagues analyzed dietary habits of 106 families with one child 3 to 5 years old at the start of the study. They collected three-day food diaries for the children one to four times each year. The diaries included detailed descriptions of the food, portions, brands and recipes consumed over a 12-year period from preschool to adolescence. Researchers determined which dietary factors might be associated with excessive gains in body fat during that period. They studied macronutrients such as fat, protein and carbohydrates and micronutrients, such as calcium and other minerals. They also studied intake of foods in each of the major food groups in the USDA's food guide pyramid. The researchers assessed body fat by measurements of children's height and weight as well as skinfolds from five sites on the body.

Children with higher-fat diets (35 percent of calories or more) and lower-fat diets (below 30 percent of calories) gained more weight throughout childhood than those who had moderate intakes of fat (30 to 35 percent of calories).

By early adolescence, children with generally high-fat diets had an average skinfold measurement of 104.6 millimeters (mm) and those with low-fat diets had 92.2 mm. In contrast, children with moderate fat intakes had 74.7 mm of body fat.

"While it is not surprising that children with a high-fat diet had excessive gains in body fat, we were surprised that children on low-fat diets also had excessive gains in body fat," Moore said.

The researchers found that children with the lowest intakes of dairy products gained much more body fat over an eight-year period. One third of children in the study had low dairy intake (less that 1 servings per day for girls and less than 1 servings per day for boys). These children had gained about three millimeters more skinfold fat each year than children with moderate to high intakes of dairy products. Increased consumption of fruits and vegetables was also associated with lower gains in body fat.

"Animal studies suggest that calcium may play a role in fat metabolism," Moore said. "A diet low in calcium may increase the levels of certain circulating hormones that in turn promote the storage of energy in fat cells. Restricted calcium intake may lead not only to increases in weight and blood pressure, but also to a reduction in bone density in the growing child."

Increased obesity is "part of the price we're paying" for the convenience of high-fat fast-food meals, prepackaged dinners and takeout foods, Moore said.

The American Heart Association says the best diet includes a moderate consumption of dietary fat with high intakes of fruits, vegetables and dairy products.

Other researchers in the study were Martha R. Singer, M.P.H., R.D., M. Loring Bradlee, M.S., and R. Curtis Ellison, M.D.

Source: Eurekalert & others

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