Phytate and Zinc intakes of New Zealand toddlers aged 12-24 months

Abstract

Statement of the problem: Phytate is primarily found in cereals and legumes and is the major inhibitor of zinc absorption. The United States of America, Australia and New Zealand currently have no information regarding the phytate content of food items in their food composition databases because most studies have been completed in developing countries where the phytate intake is high and zinc deficiencies have commonly been reported. A recent study in Otago, New Zealand, found that serum zinc concentrations of toddlers were low despite the toddlers having an adequate intake of zinc. The current study aimed to assign phytate values to mixed dishes and to other food items in the New Zealand food composition database, FOODfiles, that had not already been assigned phytate values by an earlier Master of Dietetics student, and to use this information to determine whether phytate is likely to be affecting zinc absorption in toddlers who were 12-24 months of age.

Methods and procedures: The Candidate assigned phytate values by using values from published literature and by developing recipes for mixed dishes. The developed recipes were adjusted for yield factors and, where appropriate, for fermentation. Previously assigned phytate values were adjusted for the extraction rate of New Zealand white flour and all phytate values were checked and corrected for accuracy. The dietary intakes of 154 toddlers from Wellington, North Canterbury and Dunedin who were 12-24 months of age had previously been collected as part of the Eating Assessment in Toddlers study by using five-day weighed diet records. The Candidate used this information to determine the phytate and zinc intakes of the toddlers and to calculate the phytate:zinc molar ratio. Results: A total of 906 phytate values were assigned to food items in FOODfiles including values for 453 recipes developed for mixed dishes. Overall, 6.5% of the toddlers had a zinc intake below the Estimated Average Requirement of 2.5mg per day, however, significantly more South Island toddlers (15%) had a zinc intake below 2.5mg per day compared to North Island toddlers (4%) (P=0.0091). A total of 7% of the toddlers had a phytate:zinc molar ratio above 15 for their overall diet, but 59% (of the subset of participants tested) had a phytate:zinc molar ratio above 15 at ‘breakfast’. The major sources of phytate in the toddlers’ diets were bread (27%) and breakfast cereals (23%). The major sources of zinc in the toddlers’ diets were dairy products (26%) and meat (11%). The majority of toddlers in this study were New Zealand European (77%) with 8% identifying as Māori and 3% identifying as Pacific Island. More toddlers were from the least deprived areas of New Zealand than the most deprived areas. Conclusions: There is now an electronic version of the New Zealand food composition database which includes phytate values for all food items. Most of the toddlers from this study appear to have an adequate zinc intake, and it appears that their overall intake of phytate is unlikely to be inhibiting their zinc absorption. However, there is some suggestion that zinc absorption from ‘breakfast’ may be impaired for more than half the participants because the phytate:zinc molar ratio is so high for that meal. Biochemical testing of serum zinc concentration was not carried out in this study but would be warranted based on the findings of this study.