Promotive effect of Shoyu polysaccharides from soy sauce on iron absorption in animals and humans.

Soy sauce (Shoyu) is a traditional fermented seasoning of Japan and is available throughout the world. We investigated the effect of Shoyu polysaccharides (SPS) prepared from soy sauce on iron absorption in vitro and in vivo. First, by measuring the iron-binding capacity of SPS, it was found that SPS stabilized the solubility of ferrous iron at neutral pH's by forming a complex, Fe-SPS. Second, in experiments with animals, it was found that SPS enhanced the absorption and/or pooling of iron in organs when anemic rats were fed iron-supplemented diets. Third, in a 4-week randomized, double-blind, placebo-controlled parallel group study, healthy women were treated with 600 mg of SPS (n = 22) or placebo (n = 23) each day. After the 4 weeks, serum levels of iron, hematocrit, and hemoglobin were significantly higher (P < 0.05) in the SPS-treated than in the placebo-treated group. In conclusion, SPS of soy sauce enhanced iron absorption, and soy sauce is a potentially promising seasoning for the treatment of anemia through food.