PORTLAND, Ore. - Feb. 7, 2006 - Following a diet lower in total fat did not significantly reduce the risk of breast cancer, colorectal cancer, heart disease, and stroke in postmenopausal women. That's the conclusion from the largest ever clinical trial of low-fat diets, conducted by the National Institutes of Health's Women's Health Initiative (WHI). The findings are reported in three papers in the February 8 edition of the Journal of the American Medical Association.

Researchers at Kaiser Permanente's Center for Health Research (CHR) in Portland and other sites around the country found no significant differences in the rates of colorectal cancer, heart disease, or stroke between the group of women who followed a low-fat dietary plan and the comparison group who followed their normal eating patterns. Women in the study who reduced their total fat intake had a nine percent lower risk of breast cancer than did women who made no dietary changes, but this difference was not large enough to be statistically significant - meaning it could have been due to chance.

"At first glance, women 50 and older and their doctors may think these results from the Women's Health Initiative go against the idea that good diet and lifestyle choices can improve health," says Evelyn Whitlock, MD, MPH, senior investigator at CHR and a co-author of the breast and colorectal cancer articles. "In fact, these results do not contradict current recommendations for healthy eating based on a low-fat dietary pattern that reduces intake of saturated fats and trans fatty acids and that increases vegetables, whole grains, and fruit servings each day. Equally if not more importantly, women can reduce their cancer and heart disease risks by getting recommended colorectal cancer screening, regular mammograms, and working with their doctors to identify and manage their personal risk factors for heart disease."

The study involved 48,835 women nationwide, including 1,194 women who participated through Kaiser Permanente's Center for Health Research. Women were aged 50-79 when they joined between 1993 and 1998 and were followed for an average of 8.1 years. The study design focused on reducing total fat in the diet rather than on reducing the different kinds of fat. This reflected a widely believed - but untested theory - that reducing total fat would lower risks of breast or colorectal cancer. For heart disease, it was anticipated that reducing total fat would be accompanied by a reduction in saturated fats, which are known to contribute to heart disease.

Women in both groups in the study started at 35-38 percent of calories from fat. By the end of the first year, the low-fat diet group reduced total fat intake to 24 percent of calories from fat, but did not meet the study's goal of 20 percent. At year six, the low-fat diet group was consuming 29 percent of calories from fat. The comparison group averaged 35 percent of calories from fat at year one and 37 percent at year six. The low-fat diet group also modestly increased their consumption of vegetables, fruits, and grains.

The U.S. Dietary Guidelines for Americans recommend that adults keep total fat intake between 20 and 35 percent of calories, with saturated fats at less than 10 percent of calories and most fats coming from such sources of polyunsaturated and monounsaturated fats as fish, nuts, and vegetable oils. For people with heart disease or at high risk for heart disease, targets for saturated fats may be lowered further.

"These results from the Women's Health Initiative show that modest reductions in dietary fat after the age of 50 do not have as much benefit as we expected," says Victor J. Stevens, PhD, senior investigator at CHR and a co-author of the low-fat diet and heart disease article. "From population comparison studies, we know there is a major correlation between dietary fat intake and cancer rates, but clearly this is a complex relationship that we do not yet understand. It may be that we will need a much longer follow-up period to see the full effect of dietary change on the risk of cancer and heart disease. This is why we will be following the women in this study for another five years."

This study of low-fat dietary patterns is one of the three randomized clinical trials in postmenopausal women that make up the Women's Health Initiative. The second included trials of hormone therapy - estrogen plus progestin and estrogen alone. Both trials were stopped early, estrogen plus progestin in 2002 and estrogen alone in 2004, because of increased risk of diseases like stroke, blood clots, and breast cancer. Results of the third clinical trial studying the effects of calcium and Vitamin D supplements on osteoporosis-related bone fractures and on colorectal cancer will be published in February 2006.

The WHI is the most comprehensive study to date of the causes and prevention of the major diseases affecting the health of older women. Over 15 years, the study's findings on heart disease, breast and colorectal cancer, and osteoporosis have stimulated many changes in clinical practice. The WHI is also one of the largest studies of its kind ever undertaken in the United States.

Kaiser Permanente's Center for Health Research, founded in 1964, is a non-profit research institution whose mission is advancing knowledge to improve health.

Kaiser Permanente Northwest is the nation's leading integrated health care organization. Founded in 1945, it serves more than 8.4 million people nationwide, including more than 475,000 in Oregon and Southwest Washington.

For more infomation contact:

Released: February 7, 2006