Effects of consumption of processed soy proteins on minerals and digestion in man

Most of our knowledge of digestion and utilization of minerals and other components of foods is derived from model experiments with animals. Results indicate that digestion and utilization depend not only on type of foodstuff, but also on, e.g., animal species, nutritional status and overall diet composition. Despite these limitations, such model experiments help us in delineating problem areas and in finding solutions. To verify the conclusions drawn, tests in human beings, preferably under normal living conditions, are needed. Results of animal experiments with soy protein materials indicate that no major effects from the consumption of heat-treated soy proteins are to be expected. As systematic human experiments are scarce, we carried out a large scale experiment to assess acceptation and the possible physiological effects of substituting soy proteins for conventional proteins in the usual diet. We compared two diets in a 4+4 week crossover design with 92 healthy volunteers. One diet contained a wide variety of soy protein foods, mainly made with concentrates (test diet), about 25% of the protein intake being from soy. The other diet (control) contained products made from conventional protein sources. Although most of the 100 parameters investigated showed no difference, statistically significant reactions to soy were observed in mineral metabolism and digestion. All these changes are well within normal physiological ranges, do not indicate unfavorable trends, and can be explained by adaptation to shifts in dietary composition due to substitution of soy protein materials for conventional protein sources. In a separate experiment with 12 subjects, the effect of processing soy proteins on flatulence was investigated. It was found that refining can remove up to two-thirds of the oligosaccharides stachyose and raffinose, with a parallel decrease in volume of intestinal gas production. We conclude that these results confirm the prevailing view that soy protein materials are acceptable for our daily food.