The dynamic nature of zinc availability from foods in vivo. Implications for in vitro methods

This paper presents a review of data from animal experiments demonstrating that the relative availability of zinc from foods is affected by an interaction between the source and amount of zinc consumed. Zinc availability from foods was determined by whole body counting after feeding 65Zn-labeled meals containing varying amounts of zinc. Relative to availability from zinc chloride, zinc availability from foods such as chicken, milk, and peanut butter was greater when determined using 98 rather than 16 micrograms zinc in the meal. In rats fed the higher dose of zinc, there were greater differences in zinc availability among the 15 foods studied, and zinc availability was greater from some foods than from zinc chloride. After an in vitro enzymatic digestion, neither zinc solubility nor the partitioning of zinc between low and high molecular weight substances was useful for predicting zinc availability in vivo. These data indicate that zinc availability from food is not a constant proportion of availability from a zinc salt. In view of the dynamic nature of zinc availability in vivo, the inability to accurately simulate different physiological responses to varying quantities of certain foods may limit the usefulness of in vitro methods.