Zinc Absorption Is Not Related to Dietary Phytate Intake in Infants and Young Children Based on Modeling Combined Data from Multiple Studies

Abstract

Background: It is widely understood that the 2 primary factors affecting dietary zinc absorption in adults are the quantities of zinc and phytate in the diet. Although a similar association of absorption to dietary zinc and phytate is presumed to exist in children, to our knowledge, no large-scale examination of the relation of zinc absorption to dietary and growth factors has been conducted.

Objective: The goal was to apply an adult absorption model and related models to data from zinc absorption studies of infants and children in order to determine the nature of the relation of zinc absorption to dietary zinc and phytate, age, body size, and zinc homeostatic variables.

Methods: Data from 236 children between 8 and 50 mo of age were obtained from stable-isotope studies of zinc absorption. Statistical and mechanistic models were fit to the data using linear and nonlinear regression analysis.

Results: The effect of dietary phytate on zinc absorption when controlling for dietary zinc was very small and not statistically discernable (P = 0.29). A 500-mg/d increase in dietary phytate reduced absorbed zinc by <0.04 mg/d. Absorption was observed to vary with age, weight, and height (P < 0.0001) when controlling for dietary zinc. For example, absorption from 6 mg/d of dietary zinc increased by as much as 0.2 mg/d with a 12-mo increase in age. Absorption varied with weight and exchangeable zinc pool size (0.01 < P < 0.05) when controlling for dietary zinc and age.

Conclusions: The absence of a detectable phytate effect on zinc absorption raises caution about use of dietary phytate:zinc molar ratios to predict zinc bioavailability and does not support phytate reduction as a strategy to improve zinc status of young children. The effect of age on zinc absorption and the absence of a phytate effect should facilitate estimations of dietary zinc needs in young children.

Keywords: dietary phytate; dietary zinc; infants; mathematical modeling; young children; zinc absorption.

FIGURE 1

The relation of daily absorbed zinc to dietary zinc and phytate intake in infants and young children. The surface represents the absorption response predicted by the Equation 1 model fitted to the infant/child data having TDPA values (n = 172). The vertical lines from each datum to the surface show the residual, i.e., the deviation of the point from the model’s prediction. Although an increase in absorption with increasing zinc intake is evident, there is only the suggestion of an inhibiting effect of phytate in the small downward slope of the surface with increasing phytate intake (most evident at the right side). TDPA, total daily dietary phytate (phytic acid).

FIGURE 2

The relation of daily absorbed zinc to dietary zinc and phytate intake in infants and young children. This is a 2-dimensional version of Figure 1 showing the absorption response to dietary zinc intake for selected quantities of dietary phytate. The predicted response curves for corresponding intakes from the adult model (3) are shown for comparison of the phytate effect. The difference in the magnitude of the phytate effect is evident. TDPA, total daily dietary phytate (phytic acid).

FIGURE 3

The relation of daily absorbed zinc to dietary zinc and age in infants and young children. The surface represents the absorption response predicted by the Equation 2 model fitted to all the child data (n = 233). An increase in absorption with dietary zinc or age is evident.

FIGURE 4

The relation of daily absorbed zinc to dietary zinc and age in infants and young children. This is a 2-dimensional version of Figure 3 showing the absorption response to dietary zinc intake for selected age groups. TDZ, total daily dietary zinc.