The Latest Word on Low-Fat Diets

an analysis by Ski Chilton, Ph.D.

In early 2006, the Journal of the American Medical Association released a study that overturned much of the conventional wisdom about low-fat diets. The Women's Health Initiative Dietary Modification Trial followed 48,835 post-menopausal women -- most of them overweight or obese -- for about eight years. Forty percent of the women (19,541) were instructed to decrease their consumption of fat and increase their consumption of vegetables, fruits and grains. Sixty percent of the women (29,294) were instructed to continue their usual eating habits. (1)

Compared to the usual-eating group, the low-fat group decreased its mean total fat intake by 8.2 percent, with small decreases in saturated (2.9 percent), monounsaturated (3.3 percent) and polyunsaturated (1.5 percent) fat. (1) The researchers had postulated that a low-fat diet would reduce the women’s risk of serious disease.  Instead, they were stunned to find that there were no group differences in the women’s risk of coronary heart disease, cardiovascular disease, stroke, breast cancer or colorectal cancer.  (1, 2, 3)

“Why was there a null finding in this study?” asked the authors of an accompanying editorial. Among the possible reasons: “The intervention reduced intakes of fats that increase risk of cardiovascular disease (saturated fat and trans fatty acids) but also of those that might be protective (polyunsaturated fats and monounsaturated fats.) (4)

This study is revolutionary in that it gets to the issue of what does high and low fat mean? The word “fat” is unfortunate because it carries negative connotations. Many people think that fat in the diet automatically translates into excess fat on the body. Of all the nutrients we take in, fat has the worst reputation, at least partly because it’s called fat. We have been taught this paradigm that high-fat is “bad” and low-fat is “good.”

What this study shows is that this is an antiquated way of thinking. It’s an important word on that subject. It reminds us that we shouldn’t lump all fats together, but understand that fats are divided into those that are potentially beneficial to human health and those that are potentially harmful.  The overwhelmingly positive data on dietary fish oils and cardiovascular disease conclusively shows that some dietary fats have tremendous health benefits. Consider the Greenland Eskimos, who eat an almost 50 percent fat diet and yet have practically no cardiovascular disease, heart attacks and strokes.

Literature cited.

1. Howard BV. Low-Fat Dietary Pattern and Risk of Cardiovascular Disease. JAMA 2006;295;655-666.


2. Prentice RL. Low-Fat Dietary Pattern and Risk of Invasive Breast Cancer. JAMA 2006;295;629-643.


3. Beresford SA. Low-Fat Dietary Pattern and Risk of Colorectal Cancer. JAMA 2006;295;643-654.


4. Anderson CA. Dietary Modification and CVD Prevention. JAMA 2006;295;693-694.