Three sets of mice predisposed to developing breast tumors were put on different diets: unlimited eating, intermittently cutting calories by 25 percent, or permanently reducing caloric intake 25 percent. Those on the intermittent diet fared best, with only 9 percent developing mammary tumors compared to 35 percent of those chronically restricted and 71 percent of those that ate all they wanted.
Although previous studies had shown similar results, the researchers were still surprised. Study author Margot P. Cleary, a professor at The Hormel Institute of the University of Minnesota, said her team thought periodic dieting might foster tumor growth as the return of added nourishment could jumpstart the secretion of insulin-like growth factor 1 (IGF-1), a hormone linked to the promotion of breast cancer.
"Understanding how calorie restriction provides protection against the development of mammary tumors should help us identify pathways that could be targeted for chemoprevention studies," she said in a news release. "Further identification of serum factors that are involved in tumor development would possibly provide a way to identify at-risk individuals and target interventions to these people."
This study "contributes to accumulating evidence that caloric restriction acts by altering hormone levels rather than by directly starving cancers of energy," Dr. Michael Pollak, a professor of oncology at McGill University in Montreal, wrote in an accompanying editorial. "In particular, lower levels of insulin are associated with reduced food intake, and this may be protective," he said.
Finding ways to reduce IGF-1 and insulin in the body, medically or though diet and exercise, should be further investigated, Pollak suggested.
The National Cancer Institute has more about breast cancer.