Zinc and Iron Absorption From Common Beans in Young Adult Women

Each participant will attend a total of 10 study visits. The first visit will be a screening visit to determine eligibility, and will include the administration of health history and food frequency questionnaires, and a urine pregnancy test. Participant will also be given a ASA24 24-hour dietary recall at visit 1 to return at visit 2. All subsequent visits (2 through 10) will begin with a blood sample (15 mL, or 1 tablespoon, after a 12 hour overnight fast).

Visit 2 will establish the baseline distribution of naturally occurring zinc and iron isotopes in the blood, and will include the administration of water enriched in zinc of a specific naturally-occurring isotopic mass (zinc-68, 4 mg).

Visits 2-5 will be on consecutive days, while Visit 6 will be 14 days following Visit 5. Visits 3 and 4 will include breakfast, lunch, and dinner, each containing a small serving of beans that are enriched in specific isotopic masses of iron and zinc (2 mg each of zinc-67 and iron-57, or 1 mg each of zinc-70 and iron-58). Visits 5 and 6 are for blood sampling, to measure the zinc in blood plasma (Visit 5) and the iron that has reached a 14-day equilibrium in red blood cells (Visit 6). Participants will also be given a ASA24 24-hour dietary recall at visit 6 to return at visit 7.

Visits 6-9 will be on consecutive days, starting 28 days (the approximate length of one menstrual cycle) after Visit 3, while Visit 10 will be 14 days following Visit 9. The 28-day timing is needed to minimize the potential influence of natural variation in circulating hormones, on zinc metabolism. A second urine pregnancy test will be administered on Visit 10, to detect any pregnancies that would have occurred at the time of the study meals 2 weeks prior or earlier. Participants will also be given a ASA24 dietary recall at visit 9 to return at visit 10.

Inclusion criteria

• Healthy eumenorrheic (regular monthly menstrual cycles of 25-30-days in length)
• BMI 18.5 - 30 kg/m2
• Regular consumer of beans, i.e. ≥ 4 servings per month
• Usual iron intake estimated by Food Frequency Questionnaire to be less than the Recommended Daily Allowance (RDA) of 18 mg/d (8)
• Subject is willing and able to comply with the study protocols.
• Subject is willing to participate in all study procedures.

Exclusion criteria

• Dislike or allergy to beans
• Self-reported current or recent pregnancy (within the past 12 months)
• Self-reported recent termination of pregnancy (3 months if abortion in 1st or 2nd trimester, or 12 months if in 3rd trimester)
• Self-reported plans to become pregnant during the study period
• Self-reported cancer
• Self-reported surgery without the past 12 months
• Currently taking prescription drugs, other than for contraception, or any nutritional supplements
• Any daily iron supplementation within the past 12 months.
• Currently breastfeeding
• Any medical conditions affecting iron or zinc metabolism (such as hemochromatosis or sickle cell disease)