Research technique for epidemiologic investigation of nutrition and cancer

Differential misclassification bias and dietary recall for the distant past using a food frequency questionnaire

Cases (n = 263) and controls (n = 200) returned self-administered food frequency questionnaires in 1980-1982 and again in 1986 as part of a case-control study of breast cancer. The questionnaire asked about consumption of specific food items as recalled for four different age periods. K-statistics comparing responses in the first and second questionnaires were generally similar for cases and controls and were consistent across the different age periods. The influence of recent dietary change on dietary recall diminished for the more distant past. The food frequency questionnaire was found to be more reliable for specific food items for the distant past than for the more recent past. Differential misclassification bias between cases and controls was less apparent for the more distant past. The frequency and interpretation of missing values is discussed.

Nutrient intakes of whites, blacks, and Mexican Americans in southeast Texas

Ethnic groups in the United States exhibit different patterns of cardiovascular disease and cancer morbidity and mortality. This has, in part, been attributed to differences in dietary intake. However, there is limited comparative information available regarding the dietary patterns of whites, blacks, and Hispanics residing in the same geographic area. Selected nutrient intakes were obtained by an interviewer-administered 24-hr dietary recall from 231 white, 102 black, and 98 Mexican-American persons residing in the same communities in Southeast Texas. Mean caloric intakes were highest for whites, followed by Mexican Americans and blacks. Mexican Americans had carbohydrate intakes that were significantly higher, but total fat intakes that were significantly lower, than those of whites. Blacks of both sexes had the highest cholesterol intakes and black males had the highest saturated fat intakes. Neither was significantly higher than that of whites or Mexican Americans. Overall, the mean vitamin A and C values were highest for blacks and lowest for whites, although the differences were not statistically significant. Mean calcium and phosphorus intakes were significantly higher for whites compared with those for blacks and Mexican Americans. Blacks had significantly lower mean fiber values than whites or Mexican Americans. International ethnic differences in disease distribution have long been used to provide clues to etiologic factors. National ethnic differences in disease distribution related to dietary intake can further elucidate these causative and/or preventive factors. However, to do so will require additional attention to dietary methodology of the type presented here.

Observations on the reliability and validity of the design and diet history method in the Melbourne Colorectal Cancer Study

The paper is a description of, and a practical guide to, the questions, problems, and pitfalls that can arise in the planning and execution of a large-scale epidemiological study of diet and disease; this study was an eight-year project in which diet histories were collected from over 2,000 people. Qualified dietitians obtained a quantitative diet history, which covered all foods eaten in Australia, and assessed as the most representative of the previous 20 years. Because over half of both cases and controls changed their diets in the previous 20 years, the period of recall nominated varied, but this was not a major bias. There was no effect of seasonality on recall. The average duration of the interview was one hour for both cases and controls. The response rate was 84% for cases and 94% for controls, suggesting that the time for interview of the diet history method is not a deterrent for a high response rate. In general, between-interviewer variation was small, although the intakes of total vegetables, cruciferous vegetables, and leafy green vegetables were the least repeatable. Between-interviewer differences were not found to affect the relative risks. Reproducibility of placing a dietary factor into a particular quintile of consumption was good for most foods, but it was lowest for cruciferous and leafy green vegetables. Interviewer bias regarding the dietary causes of colorectal cancer was not a major bias. Analysis of within-interviewer variation over time and analysis of recall bias were not major biases, as far as could be assessed in this study. Indirect validation of the nutritional data in the study (by comparison with other studies, by national per capita consumption, and by a comparison of energy intake with estimated energy requirements based on height, weight, and activity levels) suggested that the data are not an overestimate of intake. Cases and controls were both overestimating and underestimating their dietary intakes to a similar degree. For epidemiological studies of diet and disease, the quantitative diet history method as used here is recommended, particularly if the main objective of the study is to confirm hypotheses.

Nutrition and diet

During recent years there has been a growing awareness among both the oncologic and nutrition communities about an association between nutrition and cancer causation with the practical implication of manipulating nutrition as a means of preventing cancer. Epidemiologic correlations, prospective studies of selected populations, and dietary histories of cancer cases compared to suitable comparisons all point toward such associations. For some of the more common cancers in this country, it is thought that individuals can exert a certain amount of control over his or her own cancer risk through diet and lifestyle. As more is learned about mechanisms of mutagens and carcinogens, it may be routinely possible to inhibit, block, or reverse the cellular processes involved in carcinogenesis. It has been estimated that up to 35% of cancers may eventually be prevented by dietary modification. Until the final answers are found, it seems prudent to reduce total dietary fat intake and increase total fiber intake.