WHI & Low-fat Diets
Oakland, Calif. Tuesday, February 7, 2006 – Following a diet lower in total fat, without making any other lifestyle changes, did not significantly reduce the risk of breast cancer, heart disease and stroke, and did not reduce the risk of colorectal cancer in postmenopausal women. That is according to three studies published in the Feb. 8, edition of the Journal of the American Medical Association.
The three studies were part of the largest-ever clinical to study low-fat dietary intervention. They were carried out as part of the National Institutes of Health’s Women’s Health Initiative (WHI). Researchers at 40 centers nationwide, including Kaiser Permanente, followed 48,835 postmenopausal women for eight years. The study was designed to evaluate a low-fat dietary pattern’s effect on the risk of cancer. However, investigators also used the data to review the effect on cardiovascular disease.
The researchers found there were no significant differences in the rates of colorectal cancer, heart disease, or stroke between the group who followed a low-fat dietary plan and the comparison group who followed their normal dietary patterns. Although the women in the study who reduced their total fat intake had a 9 percent lower risk of breast cancer than did women who made no dietary changes, the difference was not large enough to be statistically significant.
“This shows that simply reducing the total fat in your diet is not, by itself, enough to reduce your risk of heart disease, stroke and colorectal cancer, and may only modestly reduce your risk of breast cancer,” said Bette Caan DrPH, a nutritional scientist, and one of the lead investigators with Kaiser Permanente’s Division of Research in Oakland, Calif.
By the end of the first year, the low-fat diet group reduced average 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. Women in both groups started at 35-38 percent of calories from fat. The low fat diet group also increased their consumption of vegetables, fruits, and grains.
“The results of this study do not change established recommendations on disease prevention.” said National Heart, Lung, and Blood Institute Director Elizabeth G. Nabel, M.D. “Women should continue to get regular mammograms and screenings for colorectal cancer, and work with their doctors to reduce their risks for heart disease including following a diet low in saturated fat, trans fat and cholesterol,”
The U.S. Dietary Guidelines for Americans recommend that adults keep total fat intake between 20 and 35 percent of calories, and saturated fats less than 10 percent of calories, with most fats coming from sources of polyunsaturated fats and monounsaturated fats, such as fish, nuts, and vegetable oils. For people with heart disease or at high risk for heart disease, targets for saturated fats may be further lowered.
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 and is considered a model for future studies of women’s health.
The Kaiser Permanente Division of Research conducts, publishes, and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and the society at large. It seeks to understand the determinants of illness and well being and to improve the quality and cost-effectiveness of health care.