Overview
Fifteen female study participants will be enrolled in a randomized crossover study to measure fractional and total zinc and iron absorption from four common bean (Phaseolus vulgaris) varieties with varying phytate and polyphenolic contents. Phytate, the storage form of phosphorus in plants, and polyphenols, which contribute to the varied colors of common beans, are natural components of the beans and can reduce zinc and iron bioavailability from these foods.
Description
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.
Eligibility
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)