Zinc homeostasis in healthy infants fed a casein hydrolysate formula

Background: The results of earlier, nonquantitative studies suggested that absorption of zinc from a semielemental (casein hydrolysate) formula was in ferior to absorption from a cow's milk-based formula. The objective of this study was to compare fractional, total and net zinc absorption, and fecal excretion of endogenous zinc in the same healthy young infants when fed a c asein hydrolysate versus cow's milk-based formula. Methods: Fractional absorption of zinc and fecal excretion of endogenous zi nc were determined from measurement of cumulative fecal excretion of unabso rbed tracer and by an isotope dilution technique, respectively, after oral administration of a Zn-70 tracer with all formula feedings for 1 day. Six i nfants were assigned randomly to receive the test or control formula, and t he other formula was administered 2 to 5 weeks later. Results: Mean (+/-SD) fractional absorption of zinc from the casein hydroly sate formula (0.47 +/- 0.17) was double that from the cow's milk-based form ula (0.22 +/- 0.04; P = 0.01) with a correspondingly greater total zinc abs orption (3.23 +/- 1.67 mg Zn/day vs. 1.55 +/- 0.55 mg Zn/day; P = 0.05), Be cause the excretion of endogenous zinc in the feces did not differ between formulas (0.90 +/- 0.44 mg Zn/day vs. 0.91 +/- 0.29 mg Zn/day), net absorpt ion of zinc was also higher with the casein hydrolysate formula (2.33 +/- 1 .65 mg Zn/day vs. 0.81 +/- 0.67 mg Zn/day; P = 0.02). Conclusions: Retention of zinc appeared to be adequate to meet the needs fo r growth during feeding with cow's milk-based formula and was more than ade quate during short-term feeding with the casein hydrolysate formula. (C) 20 00 Lippincott Williams & Wilkins, Inc.