Brief communication: Effects of soy-protein diet on elevated brain lipid peroxide levels induced by simulated weightlessness.

The influence of soy-protein diet on brain lipid peroxidation in female rats was studied using a tail-suspension model of weightlessness. The study tested the efficacy of diets containing 0% or 11.1% soy-protein in 4 groups of female Sprague Dawley rats that were maintained with or without tail-suspension for a period of 3 weeks. At term, the whole brain was removed, segmented, and analyzed for malondialdehyde (MDA) as an index of lipid peroxidation. Brain levels of MDA were significantly higher in both tail-suspended groups than in the non-suspended control groups on the same diet, (p<0.05). The high soy-protein diet decreased MDA levels significantly, compared to the 0% soy-protein groups (p<0.05). Furthermore, MDA levels were significantly lower in the tail-suspended group on high soy-protein diet, compared to the corresponding 0% soy-protein group. In conjunction with previous findings in male rats, these data indicate that tail-suspension increases brain MDA levels in rats regardless of gender, and that a diet rich in soy-protein decreases the brain MDA level in both the non-suspended and tail-suspended groups. These observations imply that the soy-protein diet has a protective antioxidant effect during both the basal condition and the stressful condition.