This is a guide for those who wish to understand the complex relationships between diet and the major diseases of western civilization, such as cancer and atherosclerosis. It begins with an overview of research strategies in nutritional epidemiology, a relatively new discipline that combines the body of detailed knowledge gained by nutritionists in this century with methodologic approaches developed by epidemiologists to study determinants of diseases with multiple etiologies and long latent periods. Learning about the effects of diet begins with its measurement; thus a major part of the book is devoted to methods of dietary assessment using data on food intake, biochemical indicators of diet, and measures of body size and composition. The reproducibility and validity of evidence from each approach and the implications of measurement error are considered in detail. The analysis, presentation, and interpretation of data from epidemiologic studies of diet and disease are discussed; particular attention is given to the important influence of total energy intake on findings in such studies. As examples of methodologic issues in nutritional epidemiology, three topics are examined in depth: the relations of diet and coronary heart disease, fat intake and breast cancer, and vitamin A and lung cancer.