Effect of phytate removal on zinc absorption from soy formula

Low zinc bioavailability from soy formula may be the result of the formula's phytate content. We assessed the effect of phytate removal from soy formula on Zn absorption using infant rhesus monkeys and suckling rat pups as animal models. Zn absorption in monkeys, as determined by whole-body counting, was 65% from human milk, 54% from monkey milk, 60% from whey-predominant formula, 46% from casein-predominant formula, and only 27% from conventional soy formula (0.621 mmol phytate/L). In contrast, Zn absorption from dephytinized soy formula (0.067 mmol phytate/L) was 45%. In suckling rats, Zn absorption from conventional soy formula was only 16% vs 47% from dephytinized soy formula. Phytate concentration in a variety of experimental soy formulas was inversely correlated to Zn absorption. These results suggest that the low bioavailability of Zn from soy formula is a function of its phytate concentration and can be overcome by the removal of phytate.