June 8, 2005
Milk Can be Too Much of a Good Thing
Drinking more than recommended amounts tied to weight gain, study suggests
Teens who drink more than recommended levels of milk may actually gain weight, rather than lose it, new research suggests.
The study was designed to examine dairy industry suggestions that drinking milk promotes weight loss, the Boston-based scientists said. Instead, they found that drinking more milk leads to overweight among teens, although those who became overweight drank more than is recommended by the National Dairy Council's dairy promotion campaign.
"My main concern is that kids who are overweight think they can drink four or five glasses of milk as a magic bullet to lose weight. They should know that large quantities are not going to help them lose weight," said Catherine S. Berkey, a biostatistician at Brigham and Women's Hospital and Harvard Medical School and lead author of the study, which was conducted by the two institutions.
A spokeswoman for the National Dairy Council said the promotion campaign says consumption of dairy products has been shown to promote weight loss in adults, but it does not make those claims for children. The council's 3-A-Day-of-Dairy campaign recommends three daily servings of milk, yogurt or cheese as a way to maintain a nutritious diet.
"Our program is aimed at adults, moms who want to lose weight. Studies find that calcium in dairy products has some effect on losing weight in combination with reducing calories and exercising. The calcium helps the body work more efficiently. But in no way, shape or form is the program ever targeted to kids," said Deanna Segrave-Daly, a dietician and council spokeswoman.
"To me this is a story about calories. If you're going to eat and drink more than is recommended, you're going to gain weight," she added.
For three years, Berkey and her colleagues followed the diets of approximately 13,000 children, aged 9 to 14 years, starting in 1996. The children were part of a Growing Up Today Study, and children of participants in the Nurses' Health Study II.
The results of the study appear in the June issue of the Archives of Pediatrics & Adolescent Medicine.
After compensating for physical activity, maturation and height growth, the researchers found that those boys and girls who drank more than three servings of milk a day were 25 percent more likely to become overweight than those who drank two to three servings a day. Twenty-three percent of the boys and 15 percent of the girls drank more than three servings per day.
Berkey said the teens in the study drank more milk than children in the general population, perhaps because they're children of nurses who might be more aware of nutrition and diet. Most children, according to Segrave-Daly, drink less than one glass of milk a day.
Berkey said the weight gain appeared to result from the calories in the milk rather than something particular to the milk itself. She also acknowledged that the study did not rule out the chance that the calories could have come from other sources.
Surprisingly, almost all the children in the study drank low-fat milk rather than whole milk, and the authors believe that estrone and whey protein in dairy products may cause weight gain.
Rachel Novotny, head of the Department of Human Nutrition Food and Animal Sciences at the University of Hawaii, said this latter finding was the most interesting part of the study.
"The bottom line is still the calories, but the question is whether calories from different sources are healthier -- and this study doesn't change thinking about that," she said. "But the marginal finding that skim or low-fat milk or whole milk, at the same level of calorie intake, is the source of weight gain is an interesting hypothesis, and deserves further study."
The National Institutes of Health has more on teaching children healthier eating habits.