Dietary cholesterol and experimental mammary cancer development

The effect of high- and low-fat diets, with and without cholesterol supplementation, on the development of N-methylnitrosourea (NMU)-induced mammary tumors was assessed. Diets consisting of 1. high fat (HF) (20% lard), 2. HF + cholesterol, 3. low fat (LF) (4% lard) + cholesterol, and 4. LF were fed to F344 female rats (24 animals/group) 2 days after NMU administration, and cumulative mammary tumor incidence was monitored for a total of 26 weeks. Animals fed HF diets exhibited significantly greater tumor incidences and numbers of tumors/animal than did animals fed LF diets (p less than .0001), regardless of whether cholesterol was present in the diet. These results are consistent with the hypothesis that the mammary-tumor promoting effects of HF diets are exerted primarily by the triglyceride fraction rather than by the nonsaponifiable (sterol) fraction of total dietary fat.