Link between dairy, weight loss unclear

Among those studies are a handful of randomized clinical trials, often considered the "gold standard" of science. All were funded by the Dairy Council, and most involved Zemel, who has received nearly $2.1 million from the group since 1998.

Zemel also has patented the claim that dairy boosts weight loss, meaning every company that uses a "Slim Down with Yogurt" or similar logo has to pay him and his university. Since 2000, the patent has generated about $500,000, half of which goes to Zemel and two other patent holders.

But it's not Zemel's science that has been criticized _ it's the dairy industry's conclusions from it.

Barry Popkin, an obesity expert at the University of North Carolina at Chapel Hill, praised Zemel as a good scientist, but said the dairy industry has overreached. "We have too many contradictions and nobody's decided what the truth is," he says.

It's not for lack of trying.

The committee of scientists who drew up the 2005 federal dietary guidelines found the data inconclusive. The Centers for Disease Control and Prevention and the American Heart Association came to a similar decision.

Dr. Walter Willett, a Harvard University nutrition expert whose recent research suggests dairy doesn't help weight loss, said Zemel's studies are too small to sustain the industry's claims.

"You need to look across all the evidence," he said. "The larger randomized trials that have been done, they don't show weight loss. If anything, they show weight gain."

In part because of those contradictions, the Physicians Committee for Responsible Medicine, which advocates a vegan diet, has filed a class-action lawsuit.

The suit, which says the industry is promising weight loss to bolster weak sales, wants a judge to block the dairy ad claims. The group says most studies on the subject indicate either no link or an adverse link between milk and weight.

That view was reflected in a 2002 review of other dairy-weight studies by Susan Barr, a University of British Columbia nutrition professor. She found most studies showed no connection and two showed weight gain.

How to explain the inconsistencies? Ludwig suspects it's not the dairy itself, but how it interacts with the diet.

Perhaps people who drink milk instead of soda, for example, eat fewer calories because milk is more filling. That also means that healthy eaters could end up with too many calories overall if dairy replaces healthy, lower-calorie foods, Ludwig says.

Others suggest that dairy eaters' overall healthier lifestyles could explain the weight loss. Some studies found that people who don't get enough calcium weigh more. But that might signal poor diet, rather than any special effect that dairy has on weight.

Whatever the reason, many scientists for now are putting their conclusions on hold as they await more evidence.

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