Epidemiology of Nutrition, Diet, and Cancer Risk

This chapter reviews the Epidemiology of Nutrition, Diet, and Cancer Risk from observational data on the association between nutrients, dietary patterns, and the risks of common forms of cancer and discusses potential causal inferences and possible nutritional intervention strategies for cancer prevention and control. There are two major aspects in nutrition and cancer, identifying carcinogenic and anticarcinogenic effects from dietary patterns, components, chemicals, nutrients for reduction of cancer risk, and improvement of clinical outcomes. Following successes in identifying the causal association of tobacco smoking with lung cancer, epidemiologists in the 1960s began to seriously examine associations of diet, nutrition, and cancer risk. The Bradford-Hill criteria were established in 1965 and are the most widely referenced criteria for establishing causal inferences from epidemiological data. The identification of aflatoxin B1 from diet as a group 1 carcinogen is a typical application of causal inference using the Bradford-Hill criteria in nutritional epidemiology. These criteria were developed during an early era of epidemiology when many modern advances in genetics, molecular biology, toxicology, exposure science, and statistics had not yet occurred. Many recent scientific advances have increased the options for the exploring potential cause-and-effect relationships in diet, nutrition, and cancer risk using modern epidemiological methods combined with insights from molecular biology, precision oncology, and personalized nutrition. Epidemiological research has traditionally formed the basis for dietary guidance issued by cancer organizations and government panels. As new science is integrated into epidemiology, the recommendations made are likely to be improved and made more specific. Currently, cancer prevention guidelines advocate a diet rich in fruits, vegetables, and whole grains, suggest limiting sugary foods and beverages, red and processed meats, sodium, and alcohol, and recommend avoiding foods contaminated with carcinogens. Some dietary supplements such as vitamins, minerals, and green tea have also been examined in research studies but have not been widely recommended despite their frequent use by many healthy individuals and cancer patients. Overweight and obesity-associated metabolic abnormalities are increasing around the world that are associated with cancer risk, due to overconsumption of energy-dense, high fat, glycemic load, sugary, and salty foods. Typically, individuals following a modern diet do not meet daily recommendations for fruit, vegetable, or whole grain consumption. While there is much more to learn about personalized nutrition and precision oncology, the recommendations that have emerged from decades of epidemiological research into the connections between nutrition and cancer form a valuable store of information that can be expanded as our understanding of carcinogenesis continues to evolve with new research. Over the past decades, a number of large intervention studies using a randomized controlled trial design have attempted to obtain final proof of a nutrient-cancer causal relationship. For many reasons, some of these large trials have failed to demonstrate the benefit of nutritional intervention because of the chosen endpoints, limited dose levels, and short duration. These results were at odds with the epidemiological data which inspired them. Results of some large trials have confused the public and led to press reports questioning any relationship of nutrition to cancer. A new approach is clearly needed where epidemiology provides part of the overall evidence. In this chapter, we recommend a research strategy that can integrate information from laboratory and animal studies to lead to common sense public health recommendations that are feasible and acceptable by public.