August 5, 2009

Are Your Eating Habits Putting You At Risk for Breast Cancer?

How you eat may be just as important as how much you eat, if mice studies are any clue. Cancer researchers have long studied the impact of diet on breast cancer, but results to date have been mixed.

New studies show that intermittent calorie restriction provided greater protection from mammary tumor development than did the same overall degree of restriction implemented in a chronic fashion. Researchers believe the answer may lie in the alteration of hormone levels that occurs with intermittent calorie restriction.

The researchers compared changes of a growth factor (IGF-1) in relationship to chronic and intermittent calorie restriction methods and tumor development in 10-week old female mice at risk to develop mammary tumors.

The overall degree of restriction was 25 percent calorie reduction compared to control mice. Mammary tumor incidence was 71 percent in the control mice who ate the amount of food they wanted, 35 percent among those who were chronically restricted and only nine percent in those who intermittently restricted calories.
The researchers were initially surprised by these findings. First, the prevailing wisdom is that the overall degree of calorie restriction is proportional to the degree of mammary tumor prevention. Second, researchers originally thought that intermittent calorie restriction might enhance tumor growth due to growth factors being secreted in response to re-feeding.

"Understanding how calorie restriction provides protection against the development of mammary tumors should help us identify pathways that could be targeted for chemoprevention studies," Margot P. Cleary, Ph.D., professor at the Hormel Institute, University of Minnesota was quoted as saying. "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."

In an accompanying editorial, Michael Pollak, M.D., professor of oncology at McGill University and director of the Cancer Prevention Center at the Jewish General Hospital in Montreal, wrote that this study "contributes to accumulating evidence that caloric restriction acts by altering hormone levels rather than by directly starving cancers of energy. In particular, lower levels of insulin are associated with reduced food intake, and this may be protective."

Based on varied findings from clinical trials, Pollak suggested lifestyle and pharmacologic methods to reduce IGF-1 and insulin deserve ongoing investigations. Cleary agreed, stating that these results may provide interest to more aggressively pursue cancer prevention studies related to calorie restriction.

"Humans frequently regain lost weight, discouraging the application of calorie restriction protocols for disease prevention," Cleary said. "We hope these studies will identify biomarkers and/or pathways that could be used in human studies to determine agents that would mimic calorie restriction."

SOURCE: Cancer Prevention Research, August 3, 2009