Phytate and zinc bioavailability.
This review discusses evidence from human studies on the effects of dietary phytate on zinc bioavailability. In vitro and animal experiments have implicated calcium as a potentiating factor because it reacts with phytate, and zinc binds to the precipitate. Magnesium also reacts similarly to calcium, but most studies have not considered this factor. Protein provides amino acids, some of which are able to desorb zinc from the precipitate and improve bioavailability. Some predictive ratios, derived from animal studies, have been directly applied to human studies. The studies reviewed included those on: zinc status of groups, apparent absorption of zinc in normal subjects and ileostomists, true absorption using a stable isotope, plasma tolerance, and the accumulation in the body of a radioisotope. It was concluded that detrimental effects of phytate could be demonstrated on zinc bioavailability, but that the studies had not been designed specifically to demonstrate whether the interactions found in animal studies also apply to humans. It is suggested that more targeted research is required before predictive ratios are used for humans.