Submitted to: American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 7/1/2005
Citation: Hambidge, K.M., Krebs, N.F., Westcott, J.L., Sian, L., Miller, L.V., Peterson, K.L., Raboy, V. 2005. Absorption of calcium from tortilla meals prepared from low-phytate maize. American Journal of Clinical Nutrition. 82(1):84-87 Interpretive Summary: Interpretive Summary: Calcium is a nutrient important to human health, especially for healthy bones. Populations that rely on grain crops such as maize for staple food are at risk for calcium deficiency in part because grain crops contain substantial amounts of phytic acid. Phytic acid binds to calcium in the intestinal tract, reducing the amount that is absorbed and used by the body. This study evaluated the retention of calcium by individuals who consumed test meals consisting of tortillas prepared using either normal maize or Low Phytate maize. Calcium retention from Low Phytate tortillas was about 40% greater than that from normal tortillas. Therefore the use of Low Phytate maize by populations that rely on maize for their basic food would improve their mineral nutritional health, particularly with respect to calcium.
Technical Abstract: Technical Abstract: Fortification of maize with calcium has been achieved for millenia in Central America by the process of nixtamalization. Bioavailability of calcium is, however, compromised by phytate, present in large quantities in maize kernels and only modestly reduced by nixtamalization. The objective of this study was to compare absorption of calcium from tortillas prepared from a low phytate maize with that from tortillas prepared from maize with a typical phytate content. Five healthy adult women were fed two test meals of approximately 150g tortillas in lieu of breakfast at one month intervals. On one occasion the tortillas were prepared from a maize with approximately 60% phytate reduction (lpa1-1) and on the other occasion from the matching isohybrid wild type maize. 44Ca (0.3mg/kg body weight) was administered in water as an extrinsic label commencing midway through the test meal and 42Ca (0.06 mg/kg body weight) was administered intravenously immediately after the test meal. Isotope ratios of 42Ca/43Ca and 44Ca/43Ca were measured by inductively-coupled plasma mass spectrometry in urine collected from 16-24 hrs after administration of the intravenous tracer and prepared by the oxalate precipitation method. Fractional absorption of calcium was determined by a dual isotope ratio technique. Mean fractional absorption from tortillas prepared from the low phytate maize was 0.50 ± 0.03 compared with a mean of 0.35 ± 0.07 from the control maize (p = 0.01). The increase in quantity of calcium absorbed could be of practical importance for calcium nutriture when intake of dairy products is limited.