Some asking: Is whole milk healthier after all?

U.S. guidelines have long recommended people steer clear of whole milk, and for decades, Americans have obeyed. Whole-milk sales fell. It was banned from school-lunch programs. Purchases of low-fat dairy rose.

"Replace whole milk and full-fat milk products with fat-free or low-fat choices," says the Dietary Guidelines for Americans, the federal government's influential advice book, citing the role of dairy fat in heart disease.

Whether this shift has made anyone healthier is an open question among scientists. Some recent evidence indicates that just the opposite might be true: Millions might have been better off had they stuck with whole milk.

Scientists who tallied diet and health records for several thousand patients over 10 years found, for example, that contrary to the government advice, people who consumed more milk fat had lower incidence of heart disease.

By warning people against full-fat dairy foods, the U.S. is "losing a huge opportunity for the prevention of disease," said Marcia Otto, an epidemiology professor at the University of Texas, and lead author of the research, which was funded by government and academic institutions, not the industry. "What we have learned over the last decade is that certain foods that are high in fat seem to be beneficial."

This year, as the Dietary Guidelines for Americans undergoes one of its periodic updates, those writing it must confront what may be the most controversial question in all of nutrition: Does the consumption of so-called saturated fats - the ones characteristic of meat and dairy products - contribute to heart disease?

The dietary science has drawn the skepticism of some on Capitol Hill. On Wednesday, a House committee will air concerns regarding the evidence for the guidelines with Agriculture Secretary Tom Vilsack and Health and Human Services Secretary Sylvia Burwell.

Some, including representatives of the American Heart Association, disagree with the idea that there is no evidence that reducing saturated fats should be a priority. In their view, the evidence arises from these two ideas: Consuming saturated fats raises levels of so-called bad cholesterol in the blood, and that higher levels of "bad" cholesterol, in turn, raises risks of heart disease.

They point to the trials of statins, which show that the drugs lower "bad" cholesterol levels and lower risks of heart disease.

There is a "mountain of evidence" explaining how consumption of saturated fats raises heart- disease, risk said Penny Kris-Etherton, a nutrition professor at Pennsylvania State University and a former member of the Dietary Guidelines advisory committee.