Zinc

Absorption of zinc from soy protein meals in humans

Sandström B, Kivistö B, Cederblad A

J Nutr 1987 Feb 117:2 321-7

Abstract

The absorption of zinc from soy protein-containing meals was studied in healthy human subjects by means of extrinsic labelling with 65Zn and whole body counting. Three types of soy protein, a soy flour, a soy concentrate and a soy isolate, were used in two types of meals: one consisting of rice and meat sauce and the other of white or whole-meal bread. Thirty and 100% of the protein of the meat sauce and 50% of the protein of bread was replaced with the soy protein products. Replacement of 30% of the protein in meat sauce had a marginal effect on the percentage absorption of zinc, whereas the absolute amount of zinc absorbed was lower due to the lower zinc content in soy products than in meat. After total replacement of the meat protein, a significantly lower percentage and absolute absorption of zinc was observed. A lower absorption of zinc was observed when soy protein was added to white bread. The absorption of zinc from the whole-meal bread was low and did not change when 50% of the flour protein was replaced by soy protein. We conclude that the effect of soy protein on zinc absorption depends on the degree of replacement, the phytic acid and zinc content of the soy product and the protein content of the meal.

Effect of phytate removal on zinc absorption from soy formula.

Lönnerdal B, Bell JG, Hendrickx AG, Burns RA, Keen CL

Am J Clin Nutr 1988 Nov 48:5 1301-6

Abstract

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.