Effect of Casein and Soy Protein Isolate on Vitamin B(6) Nutritional Status in Rats

Two experiments were conducted to test the effect of casein and soy protein isolate (SPI) on the nutritional status of vitamin B(6) in rats. Adult Long-Evans rats were fed with a casein or SPI diet at a 40% protein level with (control) or without (B(6)-deficient) 7 mg of pyridoxine/kg diet. Vitamin-B(6)-deficient rats were depleted of B(6) with (experiment 1) or without (experiment 2) deoxypyridoxine. In experiment 1, each rat was loaded with 150 mg of DL-tryptophan after 5 weeks of pair feeding. The rats on the vitamin-B(6)-deficient SPI diet (SPI-B(6)) excreted twice the amount of urine xanthurenic acid in 24 h than did the rats on the vitamin-B(6)-deficient casein (casein-B(6)) diet (p < 0.05). In experiment 2, L-tryptophan was loaded in a 20-mg dose at the end of each week. The excretion of xanthurenic acid was higher in the SPI-B(6) group than in the casein-B(6) group over the 5-week period of the experiment (p < 0.05). Erythrocyte transaminase (EGOT and EGPT) activities were lower, while EGOT and EGPT indexes were higher in the SPI-B(6) group than in the casein-B(6) group (p < 0.05). The results suggest that the source of dietary protein significantly influenced the status of B(6) nutrition in these rats. Copyright 1997 S. Karger AG, Basel