| Low-Fat High-Fiber Soy-Rich Diet in Premenopausal Women (DHS)Purpose: Adherence and biologic response to a diet low in total fat (<20% kcal) and high in fruit, vegetables, whole grains and fiber (LFHF diet) will be measured in free-living, healthy, premenopausal women. Dietary assessment and biochemical measures of total fatty acids, antioxidants and phytoestrogens will be used to quantify adherence and biologic response within and among groups. The supplemental effect of soy on these parameters beyond those observed with the LFHF diet alone (and added to the usual diet) will be evaluated further. Hormonal response relevant to potential breast cancer risk will be compared among groups over time. Background/Significance: The primary hypothesis is that adherence to a dietary pattern recommended for reduced risk of breast cancer is feasible and quantifiable via subjective and objective/biologic measures. Documentation of dietary adherence is essential before valid interpretation of metabolic responses can be formulated. A second hypothesis addresses the growing evidence regarding a potential protective benefit from a diet rich in soy isolavones, genistein, and daidzen. Previous studies of dietary intervention for prevention of breast cancer have concentrated on postmenopausal women. Studies among younger women are few and have small sample sizes, non-generalizable controlled conditions, lack of data timed to menstrual cycles, limited dietary assessment, and/or focus on single macro- or micronutrient without considering the total dietary pattern. By quantifying adherence through both subjective methods and biologic measures, further investigation of hormonal responses to diet and implications for breast cancer risk can be achieved with greater confidence. Through a randomized, placebo-controlled trial of LFHF diet with and without soy supplement, the biologic responses in a large group of premenopausal women can be measured sequentially and long term. Methods: Two hundred and twenty premenopausal women (ages 30-45, non-obese, not following low-fat diet, with regular periods) will be randomly assigned to either usual or LFHF diet and will provide dietary, biochemical, and hormonal follow-up at baseline (B) and 4 and 12 months. At 12 months, both the Intervention Group and Usual Diet Group will be randomly assigned a soy supplement (40 mg genistein) or placebo within their initial dietary assignment for an additional four months or a total of 16 months. Primary outcome measures include three 24-hour recalls; anthropometric measures; levels of urinary phytoestrogens, serum total fatty acids and plasma carotenoids collected at B, 4 months, 12 months, and 16 months; menstrual diaries; and blood samples for hormone analyses. Additional blood and urine samples will be banked for further analyses of micronutrients, lipid-lipoproteins, and other responses that may accompany adherence to the LFHF-soy-enhanced diet and be especially related to menstrual cycle duration. |
