How you eat may be just as important as how much you eat, suggest new findings published in Cancer Prevention Research. Researchers have long studied the role of diet on breast cancer risk, but results to date have been mixed. Now, new findings suggest the method by which calories are restricted may be more important for cancer protection than the actual overall degree of calorie restriction.
Previous studies have shown that intermittent calorie restriction provided greater protection from mammary tumor development than did the same overall degree of restriction, which was implemented in a chronic fashion. The researchers compared changes of a growth factor (IGF-1) in relationship to these two calorie restriction methods - chronic and intermittent - and tumor development beginning in 10-week old female mice at risk to develop mammary tumors.
The overall degree of restriction was 25 percent 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 surprised for several reasons. First, the prevailing wisdom is that the degree of protection from calorie restriction is proportional to the degree of mammary tumor prevention. Second, they originally thought that intermittent calorie restriction might enhance tumor growth due to growth factors being secreted in response to re-feeding.
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," said researcher Michael Pollak.
Based on varied findings from clinical trials, Pollak suggested that lifestyle and pharmacologic methods to reduce IGF-1 and insulin deserve ongoing investigations. "Humans frequently regain lost weight discouraging the application of calorie restriction protocols for disease prevention," added researcher Margot P. Cleary. "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."
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Source: American Association for Cancer Research