Overturning three decades of conventional wisdom, a new study of low-fat diets shows that eating less fat does not significantly reduce the risk of heart disease, stroke, breast cancer or colorectal cancer, researchers report today.
Results on weight loss from the same study, published last month, also show that reducing fats without reducing calories does not lead to significant weight loss.
The $415-million study, which tracked about 50,000 women for as many as 13 years, is by far the largest ever to address the role of fats in health and, though it hints at some potential benefits, largely closes the book on a highly publicized chapter of dietary history.
"Basically, the low-fat, high-starch diets completely struck out," said Dr. Walter Willett of the Harvard School of Public Health, whose own smaller studies have shown similar results. "This is ... the end of the low-fat era."
But, he cautioned, "the one really important point here is that it would be a serious mistake to interpret this study as 'Go and load up on sausage, butter and fast food.' "
Experts said that the results on cardiovascular disease and colorectal cancer, obtained in older women, probably applied to men as well because the disease mechanisms are the same. It is not clear, however, if changing the diet earlier in life would produce a different outcome.
The results, published today in three papers in the Journal of the American Medical Assn., might be surprising to a public that has grown accustomed to seeing more than 15,000 low-fat products on the shelves of supermarkets.
But to nutritionists and physicians working in the field over the last decade, they are consistent with new ideas about the roles of so-called good and bad fats.
"Nutrition knowledge has progressed dramatically since the study began," said Mara Vitolins, a professor of public health sciences at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., and a coauthor of the study. "Today we know that reducing total fat may not be enough -- we need to focus on the types of fat we eat."
That means reducing consumption of saturated fats like those found in meat and butter and increasing the intake of vegetable and fish oils, which studies have shown have a protective effect.
Although the study found no significant benefits from a low-fat diet, it also found no harm from the accompanying increased consumption of carbohydrates -- grains, starches and sugars.
