While the findings may seem to turn the food pyramid on its head, researcher Dariush Mozaffarian, MD, of the Harvard School of Public Health in Boston, says more study is needed to understand its public health implications.
"This is not really what we would have expected to find based on studies in men, but postmenopausal women are not men," Mozaffarian tells WebMD. "This finding may be unique to this population, but we just don't know."
Fats and Carbs Revisited
Saturated fats from the diet are the major determinate of "bad" LDL cholesterol. Diets high in saturated fats, such as those found in animal meat, cheese, milk, and baked goods can increase blood levels of LDL. The American Heart association has recommended limiting the amount of saturated fats in the diet to less that 7% as of part of a heart healthy diet.
The study involved 235 older women who were followed for three years. All the women had some plaque buildup when they enrolled in the trial, and X-ray imaging (angiogram) was used to compare arterial plaque progression at entry with that at the end of the trial.
On average, fats made up about 25% of the women's diets. In addition to having less plaque buildup, women who ate the most saturated fat had a better balance of good to bad cholesterol -- which protects against heart disease.
Replacing saturated fats with other types of fats, such as monounsaturated fats found in plant sources, did not appear to influence disease progression, but replacing fats with highly refined carbohydrates did. Higher carbohydrate intake was associated with more disease progression.
The findings are published in the November issue of the American Journal of Clinical Nutrition.
"This is consistent with the evidence that eating refined, fiber-poor carbohydrates increases heart disease risk," Mozaffarian says.
"The American Paradox"
In addition to being postmenopausal, 75% of the women in the study were overweight, one in four had diabetes and most had evidence of metabolic syndrome -- a combination of risk factors that increases the risk of heart disease and type 2 diabetes. Nutrition researcher Robert H. Knopp, MD, says it is increasingly clear that people with these heart disease risk factors do not process fats and carbohydrates in the same way that healthier people do.
In an editorial accompanying the study, Knopp wrote of an apparent "American paradox" suggesting that a high-fat diet may be more protective against heart disease for this specific, high-risk population than one that is low in fat.
"This is counterintuitive to say the least, and so the first instinct is to dismiss it out of hand as an accident," he tells WebMD. "But what intrigues me is that there are clues that there might be some truth to this."
Knopp dismisses the idea that saturated fats may be uniquely protective, however. He adds that there is a huge body of evidence showing a high saturated-fat diet to be a risk factor for heart disease.
"We now know that not all fats are bad," he says. "And we may have to change our thinking again with regard to saturated fats, at least when we talk about people with metabolic syndrome. And there is reason to believe that this association is even stronger in women than in men."