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If you regularly wash down Krispy Kremes for breakfast, don't expect a few brisk walks around the block to nullify the effects of the doughnut diet.
Researchers in USC's Arnold School of Public Health are finding evidence that high-fat diets can trump some of the benefits of regular, moderate exercise. The research, though still in its early stages with animal models, has particular ramifications for colon cancer prevention.
"Our onging research with mice that have intestinal and colon tumors demonstrates that regular moderate exercise can substantially lower the number of intestinal tumors," said James Carson, an associate professor in the Department of Exercise Science. "But when a low-fiber, high saturated fat diet is combined with exercise, the mice get no tumor reduction benefit from the exercise."
Carson's research, funded through an NIH grant that supports several colon cancer studies at USC, uses laboratory mice that carry a genetic mutation that predisposes them to develop colon cancer. Mice on a standard diet and getting regular exercise developed fewer intestinal and colon tumors when compared to those that didn't exercise. But those given high-fat diets and a regular exercise routine didn't get any protective benefit from the additional physical activity.
Exercise in regular, moderate amounts can reduce whole body inflammation, which is tied to tumor formation and growth, Carson said. Reduce inflammation and the risk of tumor formation is reduced. But diets high in saturated fats increase inflammation, and exercise--at least in Carson's studies--doesn't mitigate that effect.
"We're trying to tease out if it's the saturated fat or the extra calories that are eliminating the benefits of exercise," he said. "We know that monounsaturated fat can actually reduce inflammation, so the type of fat in the diet might be a factor, too."
The human body is programmed for spikes of inflammation--a sore throat or fever, for instance--to rev up the immune system and fight off a germ. Chronic inflammation, which can result from being overweight or obese, is a risk factor for several types of cancer.
Carson's research on the interface between nutrition, exercise, and colon cancer continues through next year with the current grant. He is also launching studies on the wasting condition that sometimes accompanies colon cancer. This wasting--which can total up to 30 percent of a colon cancer patient's weight--can be fatal and has usually been considered a side effect of cancer. But if wasting could be prevented or treated, Carson said, fewer deaths would occur.
"Many cancer deaths actually are the result of losing too much body mass," Carson said. The weight loss isn't tied to eating fewer calories; many people continue to waste with normal food consumption.
"There's a big push clinically and in the biomedical research community to understand how to keep body mass on these cancer patients, and our efforts are centered on exercise and nutrition interventions."
10/06
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