Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2008
Publication Date: 3/1/2009
Citation: Hunt, J.R., Beiseigel, J.M. 2009. Dietary Calcium Does Not Exacerbate Phytate Inhibition of Zinc Absorption By Women From Conventional Diets. American Journal of Clinical Nutrition. 89(3): 839-843.
Interpretive Summary: Phytate contained in whole grains, nuts, and legumes binds to and prevents the absorption of minerals such as calcium, iron and zinc. In studies with rats, calcium as well as phytate inhibits zinc absorption, especially from high-phytate diets. However, it is unclear whether calcium reduces Zn absorption by humans from practical diets that vary in phytate content. To evaluate this, Zn absorption was measured in 10 healthy women from four different one-day menus with low and high phytate, and moderate and high calcium contents (about 700 and 1800 mg/d). Zinc absorption was reduced by about 25% with the high, compared with the low phytate diets, but differences in dietary calcium did not affect zinc absorption, whether tested with high or low dietary phytate. Modifications in dietary phytate may be useful for improving zinc absorption from plant-based diets in developing countries. However, calcium-fortification of practical human diets does not appear to impair zinc absorption.
Technical Abstract: Background: Although Ca inhibits Zn bioavailability to rats, especially from high-phytate diets, the practical impact of Ca on Zn absorption by humans from practical diets remains unclear. Design: Using a 2X2 factorial design, Zn absorption was determined in 10 healthy women from 1-d diets with low and high phytate (about 440 and 1800 mg/d, respectively), and moderate and high Ca contents (about 700 and 1800 mg/d). Absorption was measured with extrinsically added 65Zn and subsequent whole body scintillation counting. Results: Fractional Zn absorption was significantly reduced, by approximately 10 percentage points, with the high, compared with the low phytate diets. Absolute Zn absorption was reduced by 25% from the high, compared with the low phytate diets, an absorption difference of about 1 mg/d. Differences in dietary Ca did not affect Zn absorption, whether tested with high or low dietary phytate. Conclusions: Dietary phytate reduced Zn absorption, but Ca did not impair Zn absorption whether dietary phytate was low or high.