Walter C. Willett

This Report has a number of inter-related general purposes. One is to explore the extent to which food, nutrition, physical activity, and body composition modify the risk of cancer, and to specify which factors are most important. To the extent that environmental factors such as food, nutrition, and physical activity influence the risk of cancer, it is a preventable disease. The Report specifies recommendations based on solid evidence which, when followed, will be expected to reduce the incidence of cancer.

Abstract This book is intended to increase understanding of the complex relationships between diet and the major diseases of western civilization, such as cancer and atherosclerosis. The book starts with an overview of research strategies in nutritional epidemiology—a relatively new discipline which combines the knowledge compiled by nutritionists during this century with the methodology developed by epidemiologists to study the determinants of disease with multiple etiologies and long latent periods. 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 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 paid to the important influence of total energy intake on findings in such studies. As examples of methodologic issues in nutritional epidemiology, three substantive topics are examined in depth: the relations of diet and coronary heart disease, fat intake and breast cancer, and Vitamin A and lung cancer.

The aim of this study was to evaluate the reproducibility and validity of a 61-item semiquantitative food frequency questionnaire used in a large prospective study among women. This form was administered twice to 173 participants at an interval of approximately one year (1980-1981), and four one-week diet records for each subject were collected during that period. Intraclass correlation coefficients for nutrient intakes estimated by the one-week diet records (range = 0.41 for total vitamin A without supplements to 0.79 for vitamin B6 with supplements) were similar to those computed from the questionnaire (range = 0.49 for total vitamin A without supplements to 0.71 for sucrose), indicating that these methods were generally comparable with respect to reproducibility. With the exception of sucrose and total carbohydrate, nutrient intakes from the diet records tended to correlate more strongly with those computed from the questionnaire after adjustment for total caloric intake. Correlation coefficients between the mean calorie-adjusted intakes from the four one-week diet records and those from the questionnaire completed after the diet records ranged from 0.36 for vitamin A without supplements to 0.75 for vitamin C with supplements. Overall, 48% of subjects in the lowest quintile of calorie-adjusted intake computed from the diet records were also in the lowest questionnaire quintile, and 74% were in the lowest one of two questionnaire quintiles. Similarly, 49% of those in the highest diet record quintile were also in the highest questionnaire quintile, and 77% were in the highest one or two questionnaire quintiles. These data indicate that a simple self-administered dietary questionnaire can provide useful information about individual nutrient intakes over a one-year period.