The importance of the body's need for zinc in determining Zn availability in food: a principle demonstrated in the rat.

1. The hypothesis that the availability of zinc in a food is limited by factors in the food was tested against the hypothesis that Zn absorption is homeostatically regulated by the body according to its need for Zn. 2. The experimental model used was the short-term administration to rats of a parenteral nutrition solution with no added Zn in an attempt to increase their need for Zn in an anabolic phase. 3. The absorption and retention of 65Zn from a piece of endosperm-wheat crisp-bread in rats injected intraperitoneally with the parenteral nutrition solution was more than 40% higher than that in a control group injected with physiological saline (9 g sodium chloride/l). 4. The results indicate that the availability of Zn in the bread is not fixed but variable and dependent on the body's need for Zn.