Dietary Modification Study Fact Sheet

WHAT WAS THE PURPOSE OF THE DIETARY MODIFICATION CLINICAL TRIAL?

The dietary modification (DM) clinical trial component studied the effect of a low-fat, high fruit, vegetable and grain diet on breast cancer, colorectal cancer and heart disease in postmenopausal women.

HOW WAS THE DM STUDY CONDUCTED?

There were 48,835 women aged 50-79 are participating in the DM component of WHI. Participants were either randomized to a comparison group or a dietary change group. DM study participants were followed for 8 to 12 years. Participants' health s assessed every six months by the clinical center.

WHAT WAS REQUIRED OF THE COMPARISON GROUP?

Comparison group participants maintained their usual eating habits and receive standard information on nutrition guidelines. They kept a periodic food diary and filled out health forms every six months.

WHAT WAS REQUIRED OF THE DIETARY CHANGE GROUP?

Women in the dietary change group decreased their fat intake to 20 percent of their total daily calories; increased fruit and vegetable consumption to five or more servings per day; and increased grains to six or more servings per day. Additionally, they monitored their food intake and attended nutrition group meetings to learn more about changing their diets in the first year; thereafter they attended four meetings per year. These meetings were led by registered dietitians or nutritionists.

WHAT ABOUT RECENT STUDIES SHOWING NO LINK BETWEEN DIET AND BREAST CANCER?

An analysis of seven cohort studies that was recently published in the New England Journal of Medicine¹ found no link between dietary fat intake and incidence of breast cancer. This cohort study analysis used recall of recent food intakes to calculate an estimate of total fat, which was then related to the incidence of breast cancer. This study "pooled" data from seven studies in which women were observed for several years. The validity of data from observational studies such as these depends largely on accurate dietary measurements and accurate measurements are not possible. Additionally, this study did not attempt to alter eating patterns, thus it cannot directly assess the health benefits that may follow adoption of a low-fat eating pattern.

In contrast, the WHI DM study compared the health outcomes of women randomly assigned to one of the two study groups. Randomization eliminated the possibility that other personal characteristics or lifestyles may explain differences in cancer risk.

¹D.J. Hunter, et al. "Cohort Studies of Fat Intake and the Risk of Breast Cancer -- A Pooled Analysis," New England Journal of Medicine, Feb. 8, 1996: pgs 356 - 361.