Obesity Epidemiology

88 STUDY DESIGNS AND MEASUREMENTSin epidemiologic studies of obesity and chronic diseases continue to be raised. Later inthis chapter, we will discuss the validity and reproducibility of FFQs.Diet History MethodAs discussed earlier, the diet history method was originally described by Burke in 1947. 13It consists of three parts: a detailed face-to-face interview; a cross-check food-frequencylist; and a 3-day diet record. The food-frequency list and 3-day records were used byBurke to check the internal consistency of the interview. The purpose of the diet historymethod is to obtain usual food consumption patterns. The interview typically startswith a 24-hour recall prompted by careful probing of current and past food consumptionpatterns. Interviews, often lasting 1 to 2 hours, require substantial cooperation from theparticipants.Several medium-sized prospective studies and clinical trials have used the diet historymethod. For example, in the Western Electric Study, 19 nutritionists conducted aninitial examination followed by a second interview 1 year later. Using standardized interviewsand questionnaires, they collected data on usual eating patterns, special diets, andchanges in eating habits. To gauge the internal consistency of the interview, they useda 195-item cross-check food-frequency list. Estimates of portion sizes were based onwax models of commonly consumed foods and dishes. Participants’ wives, using mailedquestionnaires, provided further information on food preparation, as did neighborhoodrestaurants and bakeries.The CARDIA diet history was modeled after the Western Electric dietary historymethod, 20 but the list of foods was expanded from 150 items to approximately 700 toaccommodate various populations and ethnic groups. Liu et al. 20 reported on the reliabilityand validity of the CARDIA Diet History in 128 young adults. The reproducibility correlationsfor the log-transformed nutrient values and calorie-adjusted nutrient values from thetwo diet histories were generally in the range of 0.50 to 0.80 for Caucasians. For AfricanAmericans, the correlations were lower, with a majority in the range of 0.30 to 0.70. Thevalidity correlations between mean daily nutrient intakes from the CARDIA diet historyand means from 7 randomly scheduled 24-hour recalls were generally above 0.50.The Diabetes Control and Complications Trial (DCCT) also used a modified Burketypediet history method. Trained dietitians interviewed participants for approximately1.5 to 2 hours to collect quantitative and qualitative information on a usual week ofdietary intake over the previous year. Schmidt et al. 21 found that 1-year reproducibilitycorrelation coefficients ranged from 0.51 for dietary fiber to 0.72 for dietary cholesterol.Conceptually, the diet history method has advantages over 24-hour recalls and FFQsbecause it collects more accurate quantitative data on long-term consumption patterns.However, the method is time consuming, expensive, and hard to standardize. Thus, it isnot often feasible for use in large epidemiologic studies involving tens of thousands ofpeople. Similar to other dietary assessment methods described earlier, the diet historymethod is prone to recall bias caused by faulty memory or problems in estimating intakefrequencies. It can also be affected by interviewer bias.BiomarkersIn that the dietary assessment methods discussed earlier are imprecise and subject tobias, the use of biomarkers to assess nutrient intake has been of great interest to the nutritionalepidemiology community. Biomarkers offer the advantages of increased reliability