Effects of soya protein on mineral Availability

There is no evidence that soy protein per se directly affects the bioavailability of minerals. Most researchers believe that soybean protein in soybean products plays a casual role in reduced bioavailability of minerals from soya. The bioavailability of mineral, particularly zinc, may decline during the processing of soya products by the formation of protein-phytic acid-mineral complexes. These complexes seem to form more readily at pH from 7 up to 8 or 10, especially in the presence of high amounts of dietary calcium. Neutralized soya protein concentrates and isolates have been shown to have relatively low zinc bioavailability for rats as compared to other soy products. Experimental evidence based upon work with the rat and chick demonstrate a highly variable bioavailability of minerals, especially zinc. Unit food processing procedures can greatly modify zinc utilization for these experimental animals. These results do not necessarily predict how man will utilize minerals from soya products. Thus far, a few published studies of humans raise hopes that man can utilize soy products in mixed diets without alterations in mineral metabolism. Considerably more basic research is needed to determine the bioavailability of minerals from soya for man and, if necessary, to develop economically feasible processing procedures that optimize recovery and functionality of soya protein, yet reduce the amount or effect of phytic acid on mineral bioavailability. The alternative action is prudent fortification of soya protein products. Fortification should be undertaken when the product has the potential or making a significant contribution to the human diet. Indiscriminate fortification is to be avoided; this could lead to induction of alternate mineral deficiencies. For example, calcium addition to diets containing phytate reduces zinc utilization, whereas zinc addition may reduce copper utilization.