The purpose of this study is to understand whether consuming flaxseed for approximately 50 days may beneficially affect the level of certain hormones in the blood thought to be involved in the development of breast cancer. This study will address the first steps toward the development of possible breast cancer prevention strategies. Differences in hormone levels (from blood samples) will be compared between two groups of women - those in the group assigned to eating ground flaxseed daily and those in the control group (with no change in diet).

PRIMARY OBJECTIVES:

I. Evaluate whether a dietary flaxseed intervention among post-menopausal women influences circulating levels of sex steroid hormones and estrogen metabolites (including estradiol, estrone, 2-hydroxy(OH)-/16-OH-estrone ratio, SHBG, testosterone, 2-MeOH-E1&-E2, 4-MeOH-E1&-E2) thought to be involved in the development of breast cancer.

SECONDARY OBJECTIVES:

II. Assess a) the effect of flaxseed intake on serum enterolignan levels (lignan biomarker), b) the relationship between serum enterolignan and sex hormone levels.

III. Describe adherence to the flaxseed intervention.

OUTLINE: Participants are randomized to 1 of 2 arms.

ARM 1: Participants take 2 tablespoons of ground flaxseed daily for approximately 50 days.

ARM 2: Participants maintain their usual diet for approximately 50 days.

All participants will complete a questionnaire and have their blood drawn at the beginning of the study (Day 0) and at the end of the study period (approximately Day 50).

Inclusion Criteria:

1. Women residing in Toronto aged 57-64 years old, and post-menopausal.

Exclusion Criteria:

1. Consumers of flaxseed and soy (including supplements) in the past 6 months.
2. Consumers of sesame oil and sesame seeds in the past 6 months.
3. Women who took antibiotics orally in the past 6 months.
4. Women who took hormone replacement therapy or corticosteroids in the past month.
5. Non-English speaking.
6. Current chronic illnesses such as bowel disease (e.g. IBS - irritable bowel syndrome, or IBD - inflammatory bowel disease, such as Crohn's or ulcerative colitis), diabetes, heart disease (e.g. high cholesterol or high blood pressure and on medication for it), cancer, or another chronic illness.
7. Women who are currently taking blood thinners, such as Warfarin.