This randomized clinical trial studies biomarkers in post-menopausal women receiving flaxseed. Studying samples of blood, urine, and feces in the laboratory from participants receiving flaxseed may help doctors understand the effects of flaxseed on biomarkers.

PRIMARY OBJECTIVES:

I. To determine associations between the composition of the gut bacterial communities and baseline levels of the mammalian lignans and steroid hormones.

II. To determine how variation in gut microbial community composition and in steroid hormone and xenobiotic metabolizing genes affects the metabolism of mammalian lignans and steroid hormones after exposure to a lignan-rich food (flaxseed).

III. To determine how these associations differ by race (i.e., African American and European American women).

OUTLINE: Participants are randomized to 1 of 2 treatment groups.

GROUP I: Participants receive flaxseed orally (PO) daily for 6 weeks. After a usual diet "washout" period of 8 weeks, patients crossover to Group II.

GROUP II: Participants maintain a usual diet for 6 weeks. After a usual diet "washout" period of 8 weeks, patients crossover to Group I.

After completion of study treatment, participants are followed up for 30 days.

Inclusion Criteria:

• Participant must understand the investigational nature of this study and sign an Independent Ethics Committee/Institutional Review Board approved written informed consent form prior to receiving any study related procedure
• Participant must be a non-Hispanic white or non-Hispanic black (self-reported race) woman 45 to 80 years of age and postmenopausal; postmenopausal will be defined as no menstrual cycle in the past 12 months; women with a hysterectomy but with intact ovaries will be included if aged >= 55 years
• Willingness to comply with the requirements of the study

Exclusion Criteria:

• Unwilling or unable to follow protocol requirements
• Self-reported race other than non-Hispanic white or non-Hispanic black
• Use, in the 2 months prior to week 1 visit, of antibiotics, hormone replacement therapy, nonprescription hormones or herbal supplements for menopausal symptoms, or flaxseed supplements
• Nut or seed allergy
• Self-reported inflammatory bowel disease
• Gastric bypass
• Use of thyroid replacement medication (Synthroid or similar) for < 1 year
• Any condition which in the investigator's opinion deems the participant an unsuitable candidate to receive flaxseed
• Chemotherapy/radiation within the past year
• Body weight greater than 400 pounds (limit of Tanita scale)