LONGEVITY, BODY-WEIGHT, AND NEOPLASIA IN AD LIBITUM-FED AND DIET-RESTRICTED C57BL6 MICE FED NIH-31 OPEN FORMULA DIET

Groups of C57BL6 mice of each sex were assigned to one of 2 dietary re gimens, ad libitum (AL) or dietary restriction (DR), to study effects of food restriction on body weight, survival, and neoplasia. The AL an d DR groups were subdivided into a scheduled sacrifice group for exami nation at 6-mo intervals, and a lifetime group to provide longevity da ta. Necropsies and microscopic examinations were conducted on 911 anim als. In the lifetime group food consumption averaged 33.6 and 34.4 g p er week by AL males and AL females, respectively; the DR counterparts were given 40% less. The diet contained 4.35 kcal/g. The average lifet ime body weights were 34.8, 26.8, 22.6, and 21.6 g for AL males, AL fe males, DR males, and DR females, respectively, and their age at 50% su rvival was 27.5, 26.9, 31.7, and 33.5 mo. Maximal lifespan was increas ed 18% in DR males and females. Lifetime incidence of tumor-bearing mi ce was 89% and 86% for AL males and females, versus 64% for each sex o f DR mice. Dramatic reduction occurred in female DR mice in lymphoma ( 9% vs 29%), pituitary neoplasms (1% vs 37%), and thyroid neoplasms (0. 4% vs 8%). In males, hepatocellular tumors were reduced to 1% from 10% by DR. In contrast, the incidence of histiocytic sarcoma was increase d in DR females and unaffected in DR males. Tumor onset was delayed in DR animals; 87% of all neoplasms in males and 95% in females had occu rred in the AL mice by 24 mo, whereas the DR animals had only 52% and 39% of their lifetime incidence, respectively, by that age. This study provided comparative AL and DR data from C57BL6 mice examined randoml y at 6-mo intervals (cross-sectional group) in parallel with data from animals in similar cohort that was unsampled and allowed to succumb n aturally (longevity group). Dietary restriction reduced the lifetime p ercentage of tumor-bearing animals and the number of tumors per animal , and delayed the age at onset of most neoplasms.