Influence of diet and feed restriction on kidney function of aging male rats.

The influence of diet and feed restriction on kidney function was studied in aging male albino rats. Rats were fed either a commercial feed (LB) or a modified human diet (MHD) from weaning until sacrifice at either 12 or 24 mo. of age. Restricted rats were fed for only 15 out of each 48 hours. Feed restriction during either the first, the second, or both years of life was beneficial in delaying age-associated changes in kidney function as indicated by decreased proteinuria, increased in vitro transport of paraaminohippuric acid, and reduced incidence and severity of renal lesions. Urinary creatinine and blood urea nitrogen levels were also favorably influenced by restriction. Most parameters were modified by diet as well as by restriction, with MHD being generally associated with improved kidney function. Improvement in kidney function may have been more related to a reduction in protein intake than to a reduction in caloric intake as a whole.