Effect of beef fat on DMH-induced colon tumorigenesis: influence of rat strain and nutrient composition.

The modulating effect of high levels of dietary fat on chemically induced colon tumorigenesis has been studied in animal models, with conflicting results. The present study was designed to examine the influence of rat strain, stage of tumor development and micronutrient composition of the diet on 1,2-dimethylhydrazine (DMH)-induced intestinal tumorigenesis. Two strains of rats [Sprague-Dawley (SD) and Fischer-344 (F-344)] were fed one of three experimental diets. The diets contained 5 or 20% dietary fat but differed in nutrient composition and nutrient-energy ratio. After receiving the experimental diets for 4 wk, animals were treated with DMH X 2HCl (10 mg/kg body wt) once a week for 20 wk and killed 10 wk after receiving the last dose of carcinogen. Long-term administration of DMH was more toxic to F-344 rats than to SD animals, and the toxicity was potentiated by reductions in the micronutrient composition of the diet. High levels of dietary fat (20%) resulted in a barely significantly higher incidence in colon tumor (but not frequency or size) in SD rats that received the diet promoting optimal growth than did low levels of dietary fat. No effect of 20% beef fat was seen in SD animals fed a diet that produced a slower growth rate or in F-344 animals.