RATIONALE: Chemoprevention is the use of certain drugs to keep cancer from forming. Eating a diet high in isoflavones, compounds found in soy foods, may keep cancer from forming.

PURPOSE: This randomized phase III trial is studying the effects of dietary soy on estrogens in breast fluid, blood, and urine samples from healthy women.

OBJECTIVES:

• Examine the effects of two daily servings of soy on estrogen levels in nipple aspirate fluid (NAF) and serum.
• Investigate cytologic patterns of epithelial breast cells obtained from NAF as a measure of proliferation in relation to soy intake.
• Explore the effect of two daily servings of soy on cytochrome alterations of estrogen metabolism as expressed in the formation of urinary 2-, 16α-, and 4-hydroxy estrogen metabolites.
• Compare estrogen levels in NAF and serum measured at the same time during the luteal phase.

OUTLINE: This is a multicenter study. Participants are randomized to 1 of 2 intervention arms.

• Arm I: Participants partake in a high soy diet consisting of 2 daily soy servings (approximately 50mg isoflavones). The choice of soy foods will include ½ cup of tofu, ¾ cup of soy milk, or ¼ cup of soy nuts. Replacement of currently consumed foods with soy foods will be encouraged.
• Arm II: Participants will be asked to keep their soy intake below 3 servings per week. The participants will also receive general nutrition counseling.

In both arms, intervention continues for 6 months. After 6 months, participants undergo a 1-month washout period and then cross-over to the other intervention arm.

Nipple aspirate fluid, urine, and blood samples are collected periodically to measure laboratory endpoints.

DISEASE CHARACTERISTICS:

• Healthy participant

  • No diagnosis of cancer

PATIENT CHARACTERISTICS:

• Premenopausal
• Regular menstrual cycles

PRIOR CONCURRENT THERAPY:

• Not taking birth control pills or other hormones