Comparison of complementary feeding strategies to meet zinc requirements of older breastfed infants

Abstract

Background: The low zinc intake from human milk at ∼6 mo of age predicts the dependence on complementary foods (CF) to meet the zinc requirements of older breastfed-only infants.

Objective: The objective of this study was to compare major variables of zinc homeostasis and zinc status in 9-mo-old breastfed infants who were randomly assigned to different complementary food regimens.

Design: Forty-five exclusively breastfed 5-mo-old infants were randomly assigned to receive commercially available pureed meats, iron-and-zinc-fortified infant cereal (IZFC), or whole-grain, iron-only-fortified infant cereal (IFC) as the first and primary CF until completion of zinc metabolic studies between 9 and 10 mo of age. A zinc stable-isotope methodology was used to measure the fractional absorption of zinc (FAZ) in human milk and CF by dual-isotope ratios in urine. Calculated variables included the dietary intake from duplicate diets and 4-d test weighing, the total absorbed zinc (TAZ) from FAZ × diet zinc, and the exchangeable zinc pool size (EZP) from isotope enrichment in urine.

Results: Mean daily zinc intakes were significantly greater for the meat and IZFC groups than for the IFC group (P < 0.001); only intakes in meat and IZFC groups met estimated average requirements. Mean (±SEM) TAZ amounts were 0.80 ± 0.08, 0.71 ± 0.09, and 0.52 ± 0.05 mg/d for the meat, IZFC, and IFC groups, respectively (P = 0.027). Zinc from human milk contributed <25% of TAZ for all groups. The EZP correlated with both zinc intake (r = 0.43, P < 0.01) and TAZ (r = 0.54, P < 0.001).

Conclusion: Zinc requirements for older breastfed-only infants are unlikely to be met without the regular consumption of either meats or zinc-fortified foods.

FIGURE 1.

Mean (±SEM) total dietary Zn (A), including intakes from HM and complementary foods, and total absorbed zinc (B) of infants by group [meat (n = 13), IZFC (n = 14), and IFC (n = 13)]. Different lowercase letters between groups indicate significance in the pairwise comparison (P < 0.001; ANOVA with Tukey's multiple comparisons posttest). Dashed lines represent the EAR ( ) and physiologic requirement ( ) for infants of this age. EAR, estimated average requirement; HM, human milk; IFC, iron-only–fortified infant cereal; IZFC, iron-and-zinc–fortified infant cereal.

FIGURE 2.

Total absorbed zinc of infants by group [meat (n = 13), IZFC (n = 14), and IFC (n = 13)] at 9–10 mo of age correlated with the EZP (Pearson's correlation). Squares represent subjects in the IFC group, inverted triangles represent subjects in the IZFC group, and circles represent subjects in the meat group. EZP, exchangeable zinc pool size; IFC, iron-only–fortified infant cereal (dry); IZFC, iron-and-zinc–fortified infant cereal (dry).