Chapter 1 describes the worldwide epidemiology of cancer. The estimated incidence rates for various cancers worldwide in 2002 found lung, colon/rectum, and stomach to be the most common cancers in both men and women, as well as prostate and liver cancer in men, and breast and cervical cancer in women.3 The pattern of cancer distribution based on incidence and mortality rates varies geographically. In general, the predominant cancers in economically developing countries contrast to those in the industrially developed world. For Asia, Africa, and Latin America, there is a relatively high rate of cancer of the upper aerodi-gestive tract, stomach, liver, and cervix, whereas in Europe and North America there is a relatively high rate of cancer of the colon/rectum, breast, and prostate. These "Western" cancers have a strong environmental component, with diet and lifestyle factors particularly important, while in developing countries, infections with such agents as viral hepatitis and Helicobacter pylori play a key role. The geographic pattern differences in tumor incidence, prevalence, and natural history as related to food, diet, nutrition, and related lifestyle factors have been extensively reviewed by the World Cancer Research Fund and the American Institute for Cancer Research (AICR) and published in an expert report in 1997.2 An updated second report is due in 2007.
Epidemiological studies in the U.S. have defined certain specific dietary factors as having highest impact on reduction of cancer risk. The most consistent relationship is an inverse relationship between cancer risk and intake of vegetables and fruits. Additional dietary factors with evidence for decreased cancer risk include whole grains, dietary fiber, certain micronutrients (e.g., selenium, vitamin E, vitamin D, and calcium), and certain types of fat (e.g., n-3 fatty acids, particularly n-3/n-6 ratios), as well as physical activity. Other diet-related factors that increase risk include high intakes of total fat and other types of fat (e.g., saturated fat), alcohol, certain food preparation methods such as smoking, salting, and pickling foods, and high-temperature cooking of meats, as well as obesity (high body mass index).4 Results from these studies have led to organizations such as the AICR to compile specific dietary recommendations for individuals to reduce cancer risk. These general guidelines advise a reduction in fat intake (especially from animal sources), an increase in fiber intake and inclusion of a variety of vegetables and fruits in the daily diet, increased physical activity and maintenance of healthy body weight, moderation in alcoholic beverage intake, and minimization of salt-cured, salt-pickled, or smoked food.24 Indeed, recent data from the Iowa Women's Health Study Cohort of 29,564 women studied for 13 years suggest that adherence to at least a subset (6 to 9) of cancer prevention recommendations as outlined by the AICR results in a reduction in cancer incidence, and, to a lesser extent, cancer mortality.5 Based on the wealth of epidemiological and experimental data supporting a role of diet in cancer prevention, the 2005 USDA Dietary Guidelines for Americans are the first to include cancer prevention as an outcome in evaluating the evidence base for setting dietary guidelines.6
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