The calendar says it's still midwinter, but the Yoplait TV commercials are already looking ahead to summer: They suggest that eating three servings a day of Yoplait Lite yogurt may help that "itsy bitsy, teeny weeny, yellow polka dot bikini" fit better this year.
So can dairy products really help to control weight?
A number of scientists, including some on the 2005 U.S. Dietary Guidelines Scientific Committee, have been mulling that very question in recent years.
"There's a large body of epidemiological data which is very consistent and shows that people with a high dairy intake tend to weigh less and are at less risk of being obese," said Robert P. Heaney, professor of medicine at Creighton University in Omaha. "That's always promising, but it's not proof."
A few randomized, controlled studies observing individuals' responses to dairy in the diet also point to weight-loss benefits. Most of the studies are small and brief. But in general they found that people who cut about 500 calories daily from their intake and ate about three servings of dairy products per day lost more weight and trunk fat than did those who cut the same number of calories but ate less dairy food. (Researchers made sure that daily calories burned were similar for both groups.)
One 26-week study by Michael B. Zemel, director of the University of Tennessee's Nutrition Institute in Knoxville, found that dieters who ate three servings of dairy lost about twice the amount of body weight as those who skimped on dairy. Zemel, who has received funding from the Dairy Council and Yoplait, has patented his institute's findings about using dairy products for weight control. (General Mills, maker of Yoplait, had to obtain a license from the university's research foundation to cite Zemel's findings.)
So how might milk and other dairy products work to help control weight? Scientists still haven't nailed that one down. But they do know that eating too little dairy increases the body's production of a type of vitamin D known as calcitriol, but it also signals fat cells to store more fat, "so you get bigger, fatter fat cells and have more of them," Zemel said. High-dairy diets have the opposite effect, he said, producing "smaller, leaner fat cells."
Still, the evidence failed to convince the dietary guidelines scientific committee to add weight loss to the list of proven benefits of dairy consumption in its report issued in August. "The amount of publicity that this [weight loss claim] is getting is widely disproportionate to the evidence base," notes Carlos Camargo, associate professor of epidemiology at the Harvard School of Public Health and member of the guidelines committee. "If it's true, great. But somebody needs to demonstrate that in a more traditional fashion."
In the meantime, here's what experts advise:
Don't expect miracles. Before you head for the dairy case seeking a weight-loss booster, know this: "Whatever I can say about dairy or anything else for weight loss doesn't obviate the obvious," Zemel said. "There's no giant eraser for calories. . . . People often say to me, 'I eat a lot of dairy and I'm still fat.' That's because calories still count." Plus, the weight-loss effects of dairy seem to occur only if you also cut calories.
Aim for three servings of dairy products daily. That's the number recommended by the U.S. Dietary Guidelines for those who eat 1,600 or more calories daily. (For those who eat less than 1,600 calories, the guidelines suggest two servings.) A serving is an eight-ounce glass of milk, a cup of yogurt or about an ounce of cheese. There are a number of dairy products available for people with lactose intolerance.
Calcium supplements and calcium-fortified food aren't the same as dairy products. Researchers have found that people who took calcium carbonate dietary supplements lost more weight than people on a low-dairy diet -- but not as much as those on a high-dairy eating plan, Heaney said. "So there seems to be something more to it than just increased calcium," he said. "That's why I stress dairy [foods] and not calcium supplements."
Make your dairy foods nonfat or low-fat. The National Center for Health Statistics reports that adults gain about one to 1 1/2 pounds per year from ages 20 to 40. "So these should be low-fat or nonfat dairy products," said Xavier Pi-Sunyer, director of the New York Obesity Research Center at St. Luke's-Roosevelt Hospital. Prevention of weight gain, Pi-Sunyer said, "is necessary for nearly every American." Whole milk has 150 calories per eight-ounce glass -- 70 more per glass than skim. Drink milk three times daily for a year and that could work out to a 22-pound difference.
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