24-hour dietary recall and food record method Chap 4 of Nutritional epidemiology By WALTER WILLETT

Introduction 24-hour dietary recall and food record method --based on foods and amounts actually consumed by an individual on one or more specific days Food frequency questionnaires(FFQ) and diet histories—based on an individual’s perceptions of usual intake over a less precisely defined period of time

Data collection methods 24-hour dietary recall method: --an in-depth interview conducted by a trained dietary interviewer --Interviewees—subjects, parent,caretaker --The dietary interviewer solicits detailed information about everything the subject had to eat and drink from midnight to midnight to midnight of the previous day or over the 24-hour period --The importance of a skilled interviewer --Dependent on short term memory

Food preparation methods, recipe ingredients, brand name of commercial products, use of dietary supplements Interviewer(important factors in obtaining complete and accurate information): nonjudgmental manner, a neutral attitude, use open-ended questions, avoid asking questions in a manner that might influence the subject’s responses

Using computer software— Accurate quantification of amounts of foods—amount estimation tool –food containers, photographs, geometric shapes,number Using computer software— The Minnesoda Nutrition Data System (NDS): Currently the most commonly used method for dietary surveys in the U.S. Face to face, telephone interview(saving traveling time, “surprise” effect)

Food record method --food intake is recorded by the subject(or observer) at the time the foods are eaten-minimize reliance on memory --Intensive training for the subjects --The fields worker weighs the raw ingredients, as well as the individual portions of the cook dishes—determine individual food intakes --Food quantifying tools --Carefully reviewed by a trained nutritionist

Strengths and limitations of the 24-hour dietary recall and food record methods Strength (both methods) - based on actual intake to estimate absolute amount rather than relative amount of nutrients. - open ended—high level of specificity (interviews should be sensitive to cultural difference) Limitation( both method) Day to day variation

Strength (recall vs. food record) - recall does not need literacy - recall is less likely to alter eating behavior - relatively minimal respondent burden Limitation(recall vs. food record) - reliance on memory - the need for a highly trained interviewer Limitation(food record) -High level of subject motivation

Number of days and which days For group means---single day For the distribution of individual intake within the group, or relationship between individual intake and other variables—more than one day(The number of days is dependent on the studied nutrient) Work days vs. Weekend days combination of days of the week and not consecutive days Estimate of long term intake—seasonal effect For micronutrients such as vitamin A, C—food frequency questionnaire

Reducing error in data collection Factors affecting data from dietary recall : Age, gender, intelligence, mood, attention, consistency of eating pattern Comparison of mean energy intake(Recall vs. food record) Table 4-1

Reducing error in data collection Reducing error from dietary recall: Considerable training and practice of the interviewers. providing a relaxed and unhurried atmosphere for the subject. 3. asking about the previous day’s activities to help jog the subject’s memory 4. providing a list of foods 5. to use an automated system for collecting the data in which the computer provides all of the prompts for describing foods at the appropriate level of detail.

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Reducing error from food record: 1. Subject’s motivation 2. careful training of subjects in methods of keeping accurate records 3. emphasizing the importance of the subject’s contribution to the research 4. Stressing the need for timely recording of food intake 5. Encouraging subjects to maintain usual eating habits during the recording period(for ease of recording, social desirability). 6. Providing written examples 7. to review the food records by trained nutritionist ASAP.

Reducing error from both methods: 1. Between meals snacks 2. Eating out details 3. Quantification of portion sizes: Food weighing devices, photographs or food models of more than one portion size,models of geometric shapes, training of subjects in the use of food models(Table 4-2), 4. For telephone interview, tools(ex: ruler, standard measuring cups or spoons, or a notebook of photographs of different portion sizes for selected foods) can be provided to each subjects to keep at home.

Reducing error from both methods: 5. Improvement of tools: two-dimensional visuals portraying various sizes of geometric shapes,mounds, and beverage containers to facilitate amount estimation. 6. Inducing motivation: a. convincing participants the importance of the research and the critical role they play b. Monetary or other types of incentives

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Analysis of food intake data At individual level, by food group, by meal pattern(the investigation of the effects of foods when eating together) Calculation of nutrient intakes(database of food composition) The degree of specificity of food description detail required at the data collection level of coding and nutrient calculation.

Sources of error in nutrient calculation Inaccuracies in the coding of food intake data.—data entry check of the computer system, intensive training and certification of coders, 10% or 20% duplicate coding. Accuracy and representitive of the nutrient values in food composition databases. The use of outdated nutrient data Analytical methodology

Validation of 24-hour recalls and food records Reporting accuracy Accuracy of nutrient calculations Accuracy of assessing usual intake (how well the selected days of intake represent usual individual intake)

Reporting accuracy 1. omissions of food items are more common than additions. (side dishes or add-ons)(Figure4-1) 2.overestimation appears to be more frequent than underestimation for portion sizes (Table 4-4). (Beverages—best estimation, add-ons-poorest estimation) 3. The underreporting of energy intake observed in validation studies of records and recalls is more likely due to omissions in reporting foods than to underestimate of portion sizes. 4. The greatest difficulty in estimating amounts was associated with items that could not be separate visualized. .

Reporting accuracy 5. Overall, recalls tend to underestimate intake by about 10% compared with observed intake(vary considerably among individuals). 6. Flat slope syndrome: Overestimaton of portion sizes tended to be greater among those who ate smaller portions and underestimamtion by those who ate larger portions.

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Accuracy of nutrient calculations 1. (Table 4-5) calculated values tend to be higher than the analyzed values.

Accuracy of assessing usual intake 1. The use of biochemical indicator(Ch9) 2. Underreporting—underestimation—obesity,athlete,education,motivation,age (adolescent,elderly)---nutrient intakes expressed as a percentage of total energy intake have not been found to be biased,even when energy intake itself was under-reported) 3. Reproducibility —day-to-day variation, seasonal difference ---reproducible at the group level, averaging of multiple days of intake at the individual level

There are limitations and potential sources of error of dietary recalls and food records.---- be careful when using these methods to validate food-frequency questionnaires or diet histories designed for estimating long term usual dietary intake(CH 6).

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Summary Foods records and 24-hour recalls consist of specific foods consumed by an individual on one or more days greater specificity for describing foods and food preparation methods, greater flexibility for analyzing the data seldom used as the primary method for estimating usual intake in large scale epidemiologic research important in describing mean values for groups and in validating food frequency questionnaires (most commonly used method)