(Ivanhoe Newswire) – 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
