Please note I have reposted this NYTimes article because it is such an important topic to understand and something that comes up often in my counseling sessions with clients. Enjoy and if you want to see the original, please click here.
Over the last several decades, it has become accepted wisdom that consuming saturated fat, the type found in meat and butter, is bad for you. Starting in the 1960s, studies showed convincingly that saturated fat raises cholesterol levels and that these elevated levels, especially of low-density lipoprotein cholesterol, or LDL (the so-called bad cholesterol), increase heart disease. Studies also showed that consuming polyunsaturated fats — safflower, corn and soybean oils — reduced people’s levels of overall cholesterol and LDL and should be encouraged.
But new studies may be upending those assumptions. Researchers with the National Institutes of Health and other organizations recently resurrected the results of a long-overlooked Australian study conducted from 1966 to 1973, in which one group of men with heart disease increased omega-6-rich polyunsaturated fat intake to 15 percent of calories, while reducing saturated fat intake to less than 10 percent. Another group of men with heart disease continued their normal diets.
The men were followed for an average of 39 months, and those on the polyunsaturated-rich diet lowered their cholesterol levels by an average of 13 percent. But they also were more likely to die, and in particular to die of a heart attack, than those who stuck with their usual diet, which consisted of about 15 percent saturated fat.
This study — the results of which weren’t fully analyzed when it was conducted in the early days of enthusiasm for polyunsaturated oils — adds to a small but unsettling body of data suggesting that consuming polyunsaturated oils, even though they reliably lower cholesterol, may nevertheless increase your risk of heart disease.
In broader terms, the new analysis muddies the already murky issue of just how diet affects heart-disease risk and health in general. Polyunsaturated oils, while decreasing cholesterol, may simultaneously promote inflammation throughout the body, says Philip C. Calder, a professor of nutritional immunology at the University of Southampton, in England, who wrote an editorial accompanying the new analysis. This inflammation may initiate heart disease and “outweigh any possible good effect” of the oils.
More fundamentally, we don’t fully understand how high cholesterol levels contribute to heart disease. Some would argue, Calder wrote in an e-mail, that “the link between cholesterol and heart disease is not actually as strong as we think.” That possibility, while startling, lends credence to other studies showing that assiduously sticking to a diet rich in fish oils, another heart-healthful fat, doesn’t necessarily protect people from heart attacks or strokes; and that those who carry extra pounds, even to the point of being slightly obese, may live longer than people who weigh less.
None of this is to say that there are no links between diet and heart disease or longevity. We know that synthetic trans fats seem particularly risky. And that the interplay between what you eat and your particular genetics may be primary. But the truth is, at this point, we don’t truly understand how it all works. Calder said the new analysis might prompt some people to recommend lowering the use of vegetable oils, substituting animal fats instead, but that he wasn’t ready to come to that conclusion.
A version of this article appeared in print on 03/10/2013, on page MM14 of the NewYork edition with the headline: Eat your heart out.