Prevention of prostate cancer and liver tumors in L-W rats by moderate dietary restriction.

Aging conventional (CV) and germfree Lobund-Wistar (L-W) rats developed spontaneous tumors, predominantly in the prostate, liver, and adrenal glands. In CV L-W rats a 30% reduction of daily intake (natural ingredient diet L-485) had the following effects: (1) reduction of the incidence of metastatic prostate adenocarcinomas (PA) from 25.7% to 6.3% and extension of the average latent periods from 26.6 to 36.7 months; and (2) reduction of the incidence of hepatomas from 59% to 26% and extension of the average latent periods from 31.3 to 34 months. Adrenal medullary tumors developed in approximately 60% of rats older than 19 months, regardless of dietary intake and microbial status. Stromal hyperplasia developed among 36 of 78 (46%) rats older than age 30 months. Rats with PA were free of stromal hyperplasia, and the reverse was also true. Germfree L-W rats developed all of the above tumors, but the diet-related differences were not as significant as those among the conventional counterpart rats. The incidence of prostatis was reduced from 22% to 6% among the diet-restricted rats, but this lesion did not develop among the germfree rats.