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 < .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.