The American Cancer Society (ACS) publishes nutrition and exercise guidelines as a basis for communication, policy development, community activism, and ultimately influencing the dietary and exercise patterns of Americans. These guidelines, published approximately every five years, were developed by a national panel of experts in cancer research, prevention, epidemiology, public health, and policy, and reflect the latest scientific evidence on the relationship between diet and exercise patterns and cancer risk. The American Cancer Society guidelines focus on recommending individual choices regarding diet and exercise patterns, but these choices occur in group settings that neither promote nor discourage healthy behavioral patterns. Therefore, the society offers recommendations for community activities and four recommendations for individual choices to reduce cancer risk. These recommendations for community activities show that a supportive social and physical environment is essential if people at all levels of society are to have a real opportunity to make healthy behavioral choices. The American Cancer Society guidelines are consistent with those of the American Heart Association and the American Diabetes Association regarding the prevention of coronary heart disease and diabetes, as well as those defined by the 2010 U.S. Dietary Guidelines and the 2008 U.S. Resident Fitness Guidelines for health promotion. Preface The importance of weight control, exercise, and diet for cancer prevention For the vast majority of nonsmoking Americans, the most important variable determinants of cancer risk are weight control, dietary choices, and physical activity levels.1,2 More than one-third of cancer deaths that occur each year in the United States can be attributed to dietary and physical activity habits, including overweight and obesity, while another third are Although genetic susceptibility affects the risk of developing cancer, most of the variation in cancer risk in populations and individuals does not depend on genetic factors.3,4 Some behaviors such as avoiding exposure to tobacco products, maintaining a standard weight, exercising consistently, and eating a healthy diet can significantly reduce a person’s lifetime risk of developing5,6 or dying from5,7 cancer,2,8-11 and these same behaviors similarly reduce the risk of developing cardiovascular disease and diabetes.12 In fact, a recent study shows that adult men or women who are nonsmokers (former smokers or never smokers) and who live a lifestyle consistent with the 2006 American Cancer Society cancer prevention guidelines on weight control, diet, exercise, and alcohol intake significantly reduce the risk of dying from cancer, cardiovascular disease, or a combination of causes.7 While these healthy choices are personal, the social, physical, economic, and regulatory environments in which people live have the potential to contribute to or constrain them, so it is necessary for communities to work to create an environment that promotes healthy eating and exercise. Overview of the Guidelines The American Cancer Society publishes nutrition and exercise guidelines that advise health care professionals, government decision makers, and the public to reduce cancer risk through diet and other lifestyle modifications.13 This guideline is based on the total and current scientific basis for the association of diet and exercise with cancer risk, and was updated in 2012 by the American Cancer Society’s Advisory Committee on Nutrition and Exercise Guidelines. The committee evaluated data from human population studies and laboratory experiments since the last published 2006 guidelines. The committee also concluded that other comprehensive evaluations such as diet, obesity and physical inactivity are associated with cancer. The most detailed review of the multifaceted studies on nutrition and exercise is the 2007 World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) study and subsequent consecutive updates in breast cancer14 and colon cancer.15 Other comprehensive reviews or meta-analyses published in recent years were included.16 Considering the evidence derived from randomized controlled trials (RCTs), the The committee believes that there are findings about the design of this trial, the specific questions addressed, and the significance of the trial results that can be found in the context. Prospective cohort studies are more influential than case-control studies, especially when the data from several groups are valid. A case-control study based on a cancer population of at least 200 cases is considered to contain more information than a small or hospital-based case-control study. The study controlled for total energy intake, considered other dietary factors and controlled for other known risk factors, and was therefore more reliable relative to studies that failed to meet these criteria. The evidence on many issues related to nutrition and cancer is inconclusive, either because of inconsistencies in published results or because of evolving research methods on nutrition and human chronic disease. Part of the uncertainty is due to studies that focus on specific nutrients or single foods, thereby simplifying complex food and dietary patterns; and the importance of dose, timing, and duration; as well as substantial variation in nutritional status in populations. Studies of nutrition and exercise are equally challenging in randomized controlled trials and are often considered the gold standard of scientific reasoning. If the intervention is started too late, or the follow-up is too short before the benefits appear, the study may not yield an effect. In addition, randomized controlled trials of lifestyle interventions cannot be blinded to the end point of a disease such as tumor-defining statistical analysis that requires years of follow-up. No single trial can address all of the questions related to the potential impact of nutrition throughout life. In addition, many important questions about how diet, exercise, and obesity relate to tumors cannot currently be addressed in randomized controlled trials. For example, while effects on body size and dietary patterns in early childhood have substantial benefits on the risk of cancer in adulthood, it is virtually impossible to conduct randomized controlled trials beginning in infancy and extending over many years to determine the long-term consequences of interventions. Combining short-term clinical trials and observational studies with advanced knowledge of cancer-related biology so that inferences from the many complex correlations in weight, physical activity, diet, and tumor risk are largely warranted, the guideline is based on the sum of these sources, taking into account both the potential health benefits and the possible risks of taking these measures. No dietary or lifestyle pattern is completely guaranteed to prevent any disease; the potential health benefits represent the likelihood of a decrease in disease incidence, not a guarantee of total protection. These guidelines provide a summary of the available scientific information on cancer-related weight control, exercise, and nutrition intended to be followed as a whole. The American Cancer Society guidelines are consistent with cancer prevention guidelines that have been developed by other governmental and nongovernmental organizations2,10; with those of the American Heart Association17 and the American Diabetes Association18 for the prevention of heart disease and diabetes; and with those of the 2010 Definitive Dietary Guidelines for U.S. Residents19 and the 2008 Exercise Guidelines for U.S. Residents20 for general health care.