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 inferior 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 casein hydrolysate versus cow's milk-based formula.


METHODS
Fractional absorption of zinc and fecal excretion of endogenous zinc were determined from measurement of cumulative fecal excretion of unabsorbed tracer and by an isotope dilution technique, respectively, after oral administration of a 70Zn tracer with all formula feedings for 1 day. Six infants were assigned randomly to receive the test or control formula, and the other formula was administered 2 to 5 weeks later.


RESULTS
Mean (+/-SD) fractional absorption of zinc from the casein hydrolysate formula (0.47 +/- 0.17) was double that from the cow's milk-based formula (0.22 +/- 0.04; P = 0.01) with a correspondingly greater total zinc absorption (3.23 +/- 1.67 mg Zn/day vs. 1.55 +/- 0.55 mg Zn/day; P = 0.05). Because 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 absorption 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 for growth during feeding with cow's milk-based formula and was more than adequate during short-term feeding with the casein hydrolysate formula.
Krebs
N F
NF
Department of Pediatrics, University of Colorado School of Medicine, Denver 80262, USA.
Reidinger
C J
CJ
Miller
L V
LV
Borschel
M W
MW
D000042:Absorption; D000818:Animals; D001682:Biological Availability; D002364:Caseins; D018592:Cross-Over Studies; D005243:Feces; D006706:Homeostasis; D006801:Humans; D007223:Infant; D007225:Infant Food; D008297:Male; D008892:Milk; D011492:Protein Hydrolysates; D015032:Zinc / Q000378:metabolism* / Q000493:pharmacokinetics; D015033:Zinc Isotopes
D002364:Caseins; D011492:Protein Hydrolysates; D015033:Zinc Isotopes; C026375:trypticase-soy broth; D015032:Zinc