Zinc absorption and exchangeable zinc pool sizes in breast-fed infants fed meat or cereal as first complementary food

Background: The aims of this study were to compare the absorption efficiency of zinc from rice cereal and meat, with and without human milk, in 7-month-old breast-fed infants and to compare the size of exchangeable zinc pools in the infants according to the assigned complementary food. Methods: Fractional absorption of zinc was measured in male infants using extrinsic labeling with a stable isotope of zinc in a test meal of either pureed beef (n = 9) or iron-fortified infant rice cereal (n = 9). The effect on fractional absorption of the addition of human milk to each complementary food was measured in each infant with a second oral zinc isotope. Fractional absorption was measured using fecal monitoring of isotope excretion, and exchangeable zinc pool size was calculated from isotopic enrichment in urine. Results: Fractional absorption of zinc did not statistically differ between the beef (0.41 +/- 0.11) and cereal (0.36 +/- 0.05) test meals, although the trend showed that beef had higher fractional absorption than cereal. The higher intake of zinc from the beef versus cereal test meal resulted in a 16-fold greater amount of absorbed zinc (P = 0.0002). The addition of human milk caused significant decreases in fractional absorption of zinc (0.07 +/- 0.02, P = 0.01) and absorbed zinc (0.04 +/- 0.01 mg, P < 0.0001). The size of the exchangeable zinc pool did not differ according to group but was strongly correlated with mean daily zinc intake (r = 0.72, P = 0.003). Conclusions: These results confirm that meat as a complementary food for breast-fed infants can provide a rich source of dietary zinc that is well absorbed. The significant positive correlation between zinc intake and exchangeable zinc pool size suggests that increasing zinc intake positively affects metabolically available zinc.