Reversal of the promotional effect of high‐fat diet on mammary tumorigenesis by subsequent lowering of dietary fat

Abstract

Female Sprague‐Dawley rats were given 7,12‐dimethylbenz(a)anthracene at 50 days of age to induce mammary tumors, and beginning one week later were fed a high‐fat, semipurified diet containing 20% sunflowerseed oil to promote tumor development. After another 7 weeks, when one third of the rats had palpable mammary tumors, the rats were randomly assigned to five groups of 31 animals each, with the same number of tumor‐bearers in each group. One group was continued on the high‐fat diet, another was given a fat‐free diet, and the three remaining groups were fed diets containing 10% lard, butter, or coconut oil, respectively. During the next 29 weeks, rats fed the diets containing 0% or 10% fat developed significantly fewer tumors than those continued on the 20% fat diet. The diets containing 10% fat suppressed tumorigenesis at least as effectively as the fat‐free diet. Rats fed the 10% butter and 10% lard diets had growth rates comparable to those fed the 20% sunflowerseed‐oil diet throughout, and evidence of essential fatty acid deficiency was seen only in rats on the fat‐free diet. These results provide additional evidence that high‐fat diets promote development of mammary cancer and suggest that reducing the level of dietary fat might help to prevent the development and recurrence of breast cancer in humans.