The influence of replacing dietary casein with soy protein on longevity and age-related pathologic lesions of male Fischer 344 rats was investigated. Caloric intake and body weights were similar for rats on the two diets. Rats on the soy protein-containing diet had a median length of life of 844 days compared to 730 days for those on the casein-containing diet (p<.002), and the ages of the 10th percentile survivors were 937 and 857 days, respectively (p<.02). The progression of chronic nephropathy was markedly retarded by replacing casein with soy protein. Only 7% of the rats dying spontaneously on the soy protein-containing diet exhibited end-stage chronic nephropathy compared to 41% of the rats on the casein-containing diet. Clearly, the soy protein-containing diet enables ad libitum fed male Fischer 344 rats to be used as a model for aging research without the occurrence of renal failure as a major confounding problem.
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