"Let food be thy medicine and medicine be thy food." These words were spoken by Hippocrates in 440 BC, yet today they have as much application to health and the diet-cancer link as ever. To expand on this notion, Hippocrates also stated that, "All parts of the body that have a function, if used in moderation, and exercised in labors to which each is accustomed, become healthy and well developed and age slowly; but if unused and left idle, they become liable to disease, defective in growth and age quickly." Epidemiological evidence gathered over the past 50 years continues to support the belief that between 30 and 50% of all cancers could be prevented through optimal dietary selections and a physically active lifestyle (Doll and Peto 1981). Yet over this same time span we have continued to make poor food choices, reduce our level of physical activity and experience a continuing rise in the rates of overweight and obesity to the extent that obesity has become an epidemic in the U.S. Not surprisingly, these trends have undermined efforts to reduce cancer incidence. This chapter will address the role of diet, physical activity and body composition in cancer prevention. In addition to summarizing the current evidence regarding associations between diet, physical activity and cancer prevention, the content will discuss the mechanistic underpinnings by which diet and physical activity can modulate the cancer process, review current guidelines as well as propose new guidelines for reducing cancer risk through lifestyle modification, and provide tools to support the integration of cancer preventive diets and activity patterns into clinical practice.
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