What if bad fat isn’t so bad?

The St. Thomas' Atherosclerosis Regression Study (1992) Only 74 men completed this 3-year study conducted at St. Thomas' Hospital, in London. It found a reduction in cardiac events among men with heart disease who adopted a low-fat diet. There's a major caveat, though: Their prescribed diets were also low in sugar.

Flawed studies
These four studies, even though they have serious flaws and are tiny compared with the Women's Health Initiative, are often cited as definitive proof that saturated fats cause heart disease. Many other more recent trials cast doubt on the diet-heart hypothesis. These studies should be considered in the context of all the other research.

In 2000, a respected international group of scientists called the Cochrane Collaboration conducted a "meta-analysis" of the scientific literature on cholesterol-lowering diets. After applying rigorous selection criteria (219 trials were excluded), the group examined 27 studies involving more than 18,000 participants. Although the authors concluded that cutting back on dietary fat may help reduce heart disease, their published data actually shows that diets low in saturated fats have no significant effect on mortality, or even on deaths due to heart attacks.

"I was disappointed that we didn't find something more definitive," says Lee Hooper, Ph.D., who led the Cochrane review. If this exhaustive analysis didn't provide evidence of the dangers of saturated fat, says Hooper, it was probably because the studies reviewed didn't last long enough, or perhaps because the participants didn't lower their saturated-fat intake enough. Of course, there is a third possibility, which Hooper doesn't mention: The diet-heart hypothesis is incorrect.

Ronald Krauss, M.D., won't say saturated fats are good for you. "But," he concedes, "we don't have convincing evidence that they're bad, either."

For 30 years, Dr. Krauss — an adjunct professor of nutritional sciences at the University of California at Berkeley — has been studying the effect of diet and blood lipids on cardiovascular disease. He points out that while some studies show that replacing saturated fats with unsaturated fats lowers heart-disease risk, this doesn't mean that saturated fats lead to clogged arteries. "It may simply suggest that unsaturated fats are an even healthier option," he says.

But there's more to this story: In 1980, Dr. Krauss and his colleagues discovered that LDL cholesterol is far from the simple "bad" particle it's commonly thought to be. It actually comes in a series of different sizes, known as subfractions. Some LDL subfractions are large and fluffy. Others are small and dense. This distinction is important.

A decade ago, Canadian researchers reported that men with the highest number of small, dense LDL subfractions had four times the risk of developing clogged arteries than those with the fewest. Yet they found no such association for the large, fluffy particles. These findings were confirmed in subsequent studies.

Link to heart disease
Now here's the saturated-fat connection: Dr. Krauss found that when people replace the carbohydrates in their diet with fat — saturated or unsaturated — the number of small, dense LDL particles decreases. This leads to the highly counterintuitive notion that replacing your breakfast cereal with eggs and bacon could actually reduce your risk of heart disease.

Men, more than women, are predisposed to having small, dense LDL. However, the propensity is highly flexible and, according to Dr. Krauss, can be switched on when people eat high-carb, low-fat diets or switched off when they reduce carbs and eat diets high in fat, including the saturated variety. "There's a subgroup of people at high risk of heart disease who may respond well to diets low in fat," says Dr. Krauss. "But the majority of healthy people seem to derive very little benefit from these low-fat diets, in terms of heart-disease risk factors, unless they also lose weight and exercise. And if a low-fat diet is also loaded with carbs, it can actually result in adverse changes in blood lipids."

While Dr. Krauss is much published and highly respected — he has served twice as chairman of the writing committee of the AHA's dietary guidelines — the far-reaching implications of his work have not been generally acknowledged. "Academic scientists believe saturated fat is bad for you," says Penny Kris-Etherton, Ph.D., a distinguished professor of nutritional studies at Penn State University, citing as evidence the "many studies" she believes show it to be true. But not everyone accepts those studies, and their proponents find it hard to be heard. Kris-Etherton acknowledges that "there's a good deal of reluctance toward accepting evidence suggesting the contrary."

Take, for example, a 2004 Harvard University study of older women with heart disease. Researchers found that the more saturated fat these women consumed, the less likely it was their condition would worsen. Lead study author Dariush Mozaffarian, Ph.D., an assistant professor at Harvard's school of public health, recalls that before the paper was published in the American Journal of Clinical Nutrition, he encountered formidable politics from other journals.

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