Dietary Intake How Do We Measure What People Are Really Eating?

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1 Dietary Intake How Do We Measure What People Are Really Eating? Rachel K. Johnson Introduction Successful obesity treatment depends on a combination of diet modification and increased physical activity (1). The goal of diet therapy is to instruct people on long-term modifications that will reduce their energy intake (1). Frequent clinical encounters with a trained health professional (physician or registered dietitian) during the initial 6 months of therapy facilitate reaching the goals of therapy (2). An important component of these clinical encounters is assessing dietary intake during treatment and follow-up (2). The aim of this paper is to identify the most commonly used methods to estimate dietary intake, identify their strengths and weaknesses, and make recommendations for their use in the treatment of the overweight or obese patient. Traditional Dietary Intake Methodologies All traditional dietary intake methods rely on information reported by the subjects themselves. The methods include food records, food frequency questionnaires (FFQs), and 24-hour recalls. Each method has strengths and weaknesses related to their intended use, ease of administration, and validity. Food Records Food records are typically obtained for 3 to 7 days. Seven-day records were historically used as the gold standard for validating other methods (3). This was based on the tactic assumption that the self-reported information was valid or correct. However, with the advent of biomarkers, the food record is known to have many weaknesses that limit its use in validation studies. Biomarkers are variables measured in body fluids or tissue that independently reflect intake of a food component (4). Department of Nutrition and Food Science, College of Agriculture and Life Sciences, University of Vermont, Burlington, Vermont. Address correspondence to Rachel K. Johnson, College of Agriculture and Life Sciences, Department of Nutrition and Food Science, 108 Morrill Hall, University of Vermont, Burlington, VT rachel.johnson@uvm.edu Copyright 2002 NAASO Food records require literate, motivated subjects and place a high burden on the patients. The quality of the record declines in relation to the number of days recorded (5). The actual process of recording food intake can lead patients to change their food-intake patterns (6). FFQs FFQs are most commonly used in groups of people to provide estimates of usual dietary intake over time (typically 6 months to 1 year). They are often used in large cohort studies to place individuals into broad categories along a distribution of nutrient intake. The FFQ lists specific foods and asks the subject if they eat them and if so how often and how much they eat. Hence, the FFQ must be culture-specific, i.e., different lists of foods have been developed for assessing the diverse diets of such groups as Hawaiians, Japanese, Chinese, Filipinos, and whites (7). Both short (60 food items) and long (100 food items) FFQs have been developed (8), but neither were designed to assess current energy intake, an important component of diet therapy for obesity treatment. Modified FFQs were designed for identification of people with high intake of dietary fat and/or low intakes of fiber, fruits, and vegetables (9) (Figures 1 and 2). These questionnaires were developed to identify potential candidates for enrollment into intervention research studies, but they may also be useful to clinicians seeking to identify people needing diet counseling (9). Twenty-Four-Hour Recall The 24-hour recall was designed to quantitatively assess current nutrient intake. The 24-hour recall can be conducted in person or by telephone with similar results (10). This method requires only short-term memory, and if the recall is unannounced, the diet is not changed. The method is relatively brief (20 to 30 minutes), and the subject burden is less in comparison with food records. It is appropriate for use with low-income and low-literacy populations because the subjects do not need to read or write to complete the recall (11). Disadvantages of the 24-hour recall include the inability of a single day s intake to describe the usual diet (12). OBESITY RESEARCH Vol. 10 Suppl. 1 November S

2 Figure 1: Fat screener. The Fat Screener and Fruit/Vegetable/Fiber Screener and their associated scoring algorithms are the property of Block Dietary Data Systems, Berkeley, CA. You must obtain permission from the owner to use these tools. Please contact vendor for licensing: (510) , The success of the recall depends on the memory, cooperation, and communication ability of the subject. Lastly, a trained interviewer is needed. Validity of Dietary Intake Methods It is essential to assess the validity of dietary intake methods to determine if the method is measuring what people are really eating. Traditionally only face validity was determined based on comparison among methods. For example, the FFQ was often compared with 7-day food records (3). This did not actually determine if either method was valid, only if the estimates of dietary intake were comparable between the two methods. It is now believed that dietary methods should be validated using external independent markers of energy intake or biomarkers (13). Doubly labeled water (DLW) is currently the most widely used and well accepted biomarker. DLW provides an accurate measure in free-living subjects of their total energy expenditure, which is equivalent to energy intake in weightstable people. DLW is well accepted as a gold standard to determine the validity of tools designed to measure energy intake (13). Its use as a validation tool is based on the principle of energy balance; that is, if a person is weight stable then their energy expenditure, as measured by DLW, must be equal to their energy intake (14,15). Because of the high cost and sophisticated technology associated with DLW, its use to date has been confined to research laboratories around the world and does not lend itself to routine use in clinical settings. It can be used, however, in research settings to validate energy intakes obtained from the dietary intake method of choice. Low-Energy Reporting Based on DLW studies, the underreporting of food intake is known to be pervasive when people report their dietary intake. Low-energy reporting occurs when people report estimated food intakes that are lower than their true intake. When a person reports an energy intake that is not biolog- 64S OBESITY RESEARCH Vol. 10 Suppl. 1 November 2002

3 Figure 2: Fruit, vegetable, and fiber screener. The Fat Screener and Fruit/Vegetable/Fiber Screener and their associated scoring algorithms are the property of Block Dietary Data Systems, Berkeley, CA. You must obtain permission from the owner to use these tools. Please contact vendor for licensing: (510) , ically plausible, they are identified as a low-energy reporter (16). There are a number of factors associated with lowenergy reporting including age, sex, and body mass index, as well as other demographic and psychological factors (17). Based on numerous papers published over the past decade, low-energy reporting has been consistently shown to be more prevalent and more severe among obese subjects compared with lean subjects (18,19). These studies and others found that the obese underestimate their energy intake to a greater degree (ranging from 30% to 47%) than the lean. Thus, it is now well accepted that the obese are inclined to underestimate their dietary intake. These factors may be predictive of low-energy reporting, but the underlying cause is not solely because of people purposely underreporting, but also has to do with the implementation of dietary intake methods. If low-energy reporting occurred simply across the board that is, all foods and nutrients were underreported to the same degree the solution to the problem would be relatively simple. A correction factor could be added to the dietary-intake data of low-energy reporters, which would bring their intake of all nutrients into line with that of the valid reporters. Unfortunately the solution is not that simple. It has become clearer that low-energy reporters often fail to report those foods that have a bad or even sinful connotation (20). We may need to improve our probing methods or evaluate if the subject is familiar with standard measures to improve the accuracy of total energy-intake reporting. In a large U.S. survey, 1224 of 8334 adults were found to be low-energy reporters. In comparing the low-energy reporters with the non low-energy reporters, the following were among the foods less likely to be reported: cakes/pie, savory snacks, cheese, white potatoes, meat mixtures, regular soft drinks, fat-type spreads, and condiments (21). British investigators found that underreporters reported consuming significantly less cakes, sugars, fat, and breakfast cereals. However, they found no discernible differences in reports of bread, potatoes, meat, or vegetable and fruit consumption between underreporters and other subjects (22). OBESITY RESEARCH Vol. 10 Suppl. 1 November S

4 At this time there is no consensus in the literature as to whether or how much the macronutrients are differently reported. Some research suggests that low-energy reporters report lower intakes of fat, as a percentage of total energy, and higher intakes of protein and carbohydrate (17,23). Others have demonstrated that reported added sugar intake was significantly lower than measured, caused in part by the omission of snack foods from the dietary record (24). Implications of Low-Energy Reporting The phenomenon of low-energy reporting has important implications for obesity treatment. The notion that the obese often report not consuming any more calories than the lean is probably related to low-energy reporting of food intake by obese subjects (19). Hence, it is important that clinicians working with obese patients be aware of the problem and understand how to identify it. Clinicians can apply the Goldberg cut-off, which has been extensively described by Goldberg et al. (25) and Black et al. (26). The Goldberg cut-off evaluates selfreported energy intakes against estimated energy requirements and defines cut-off limits that identify the most obviously implausible intake values. The cut-off value is not valuable when applied to food frequency questionnaires because they are designed to represent a person s usual eating habits over a period of time and are not a precise measure of energy intake. Briefly, height and weight measurements are used to predict basal metabolic rate from standard formulas (Goldberg et al. recommend the Schofield equations). A ratio of estimated energy intake (EI) to predicted basal metabolic rate (BMR) is calculated as EI/BMR. The ratio can then be compared with a study-specific cut-off value (provided in ref. 25) that represents the lowest value of EI/BMR that could, within defined bounds of statistical probability, reflect the habitual energy expenditure given a sedentary lifestyle. For example, with a 4-day mean estimate of energy intake in a single subject, recorded intakes would have to be at least above 1.10 of estimated BMR to be considered plausible (25). Multiple-Pass 24-Hour Recall The multiple-pass 24-hour recall method was originally developed by the U.S. Department of Agriculture in an effort to limit the extent of underreporting that occurs with self-reported food intake (27). The method differs from the traditional 24-hour recall because the interviewer uses five distinct passes to garner information about a subject s food intake over the preceding 24 hours. The method is described in detail here. The first pass is termed the quick list. Here the subject is asked to recall everything eaten the previous day using any recall strategy they choose. The second pass is termed the forgotten food list. Here the interviewer probes the subject about possible forgotten foods (i.e., sweets, savory snacks, non- and alcoholic beverages, etc.). The third pass is termed the time and occasion. Here the subject states what time the foods were eaten and discusses the eating occasion. The fourth step is termed the detailed cycle. The subject answers standardized questions the U.S. Department of Agriculture developed to probe subjects about information pertaining to each food and clarifies food portion sizes (28). Food portion sizes can be estimated using two-dimensional food models. The food models include common household measures and dishes such as cups, spoons, bowls, and glasses; geometric shapes such as circles, rectangles, and wedges; and food-specific gram weight descriptions (29). The subjects are also asked where the food was consumed and the length of time between eating occasions. The final step is termed the final review probe. The interviewer probes to try and get any additional food items consumed recorded as part of the recall (28). Typically the multiple-pass 24-hour recalls are entered into a computer-based nutrient analysis program to obtain estimated energy intakes. The original multiple-pass 24-hour recall was shown to be accurate in young children (ages 4 to 7 years) (30). However, underreporting occurred with this method in adult women (ages 19 to 46 years) when compared with DLW measurements of total energy expenditure (11). According to Conway et al. (31), the current multiple-pass method is an accurate measure of energy intake in adult women under controlled conditions. Observer-Recorded Food Records and Recall Methods Hise et al. (32) developed a new method to improve the validity of subjective dietary records among overweight people. The method entailed people eating at a university cafeteria for 2 weeks. The food was weighed and food waste was taken into account. A 24-hour food recall was used for snacks and beverages between meals. After a 2-week measurement period, the combination of observer-recorded weighed-food records and 24-hour snack recalls were shown to be a valid measure of EI with DLW. Although the method was shown to be valid, the use of the method is limited because it would be difficult to always weigh and observe subjects intakes. Recommendations To date, no dietary intake method has been shown to be immune from underreporting in older children, adolescents, and adults (33,34). Because the multiple-pass 24-hour recall was designed to estimate current nutrient intake and attempts to minimize the problem of low-energy reporting, it is recommended as the method of choice for estimating energy intake during obesity treatment and follow-up. A 66S OBESITY RESEARCH Vol. 10 Suppl. 1 November 2002

5 single administration of the multiple-pass 24-hour recall is of little use in estimating people s usual energy intake because of the substantial intraindividual, day-to-day variation that occurs in food intake (12). Thus, it is recommended that a minimum of 3 days of intake (including 1 weekend day) be collected. This can be done in person or by telephone with similar results (10). The 3-day mean energy intake should then be assessed for underreporting using a ratio of energy intake to estimated energy requirements and established cut-offs (25). Clinicians are in need of screening questionnaires that can quickly but accurately measure changes in energy intake associated with successful outcomes of obesity treatment. Unfortunately, to date, no such questionnaire has been developed. Lowering fat intake and increasing fruit and vegetable intake are strategies that may be helpful in reducing total energy intake and promoting weight loss (2,35). Hence, the simplified fat and fiber/ fruit/vegetable questionnaire (Figures 1 and 2) might be useful in determining if a patient has lowered their fat intake and/or increased their fruit and vegetable intake. However, the validity of these questionnaires and their ability to detect dietary change in obese patients has not been tested. Conclusion Several methods are available to estimate dietary intake. Some have been developed to categorize groups of people by their long-term intake of various nutrients for epidemiological studies (FFQs). Others are designed to estimate current nutrient intake (food records and 24- hour recalls). Each method has strengths and weaknesses, and none are immune from the problem of low-energy reporting, particularly among obese subjects. The multiple-pass 24-hour recall was developed to minimize the problem of low-energy reporting and to measure current energy intake. Hence, it is recommended as the method of choice if used for at least 3 days during obesity treatment and follow-up. Quick screening questionnaires have been developed to identify people with high-fat and low-fiber/fruit/vegetable intake. These questionnaires could be used to identify patients with dietary patterns associated with successful weight loss and weight maintenance. However, their efficacy for use in this way has not been tested. Acknowledgments Dr. Johnson s research is funded in part by the Vermont Agricultural Experiment Station, project no. VT-NS The author would like to thank Ms. Amy Friedman, BS for her assistance with the preparation of this manuscript. References 1. Public Health Service. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults the Evidence Report. Bethesda, MD: Public Health Service, National Institutes of Health, National Heart, Lung and Blood Institute; Public Health Service. 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