Zinc absorption by adults is similar from intrinsically labeled zinc-biofortified rice and from rice fortified with labeled zinc sulfate

Background: Biofortification of staple food crops is a promising strategy to combat zinc deficiency, and it is of particular interest for rice and crops that are not consumed as flours and therefore not suitable for postharvest fortification. Because zinc absorption is decreased by phytic acid (PA) and perhaps other dietary components, it is important to measure the absorption of zinc from a biofortified crop before determining its efficacy. Objective: In this study, we compared the zinc absorption from zinc-biofortified rice (hydroponically enriched with ⁷⁰Zn) with that from a control rice of the same variety fortified with ⁷⁰ZnSO₄ at point of use to reach the same total zinc content of 1.1 mg/meal. Both rice meals had a PA:Zn molar ratio of 12. Methods: Fractional absorption of zinc (FAZ) was measured with the use of the double-isotope tracer ratio method in 16 apparently healthy adults [18-45 y old; BMI (in kg/m²) 19-25] who consumed 2 single meals at 4-wk intervals in random order in a crossover design. Results: The FAZ from the biofortified rice (mean ± SD: 25.1 ± 8.7%) did not differ significantly from that of the point-of-use fortified rice (mean ± SD: 20.8 ± 7.1%) (P = 0.08). Conclusions: These results suggest that the native zinc accumulated in the biofortified rice was readily released from the rice matrix and that its absorption by adults was influenced by PA and other food components in a similar way to the inorganic zinc compound added to the rice at point of use. Moreover, rice biofortification is likely to be as good as postharvest zinc fortification as an intervention strategy to combat zinc deficiency. This trial was registered at clinicaltrials. gov as NCT01633450.