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Original Research Communication |
1 From the Department of Paediatrics and Child Health, University of Sydney, Australia; the James Fairfax Institute of Paediatric Nutrition, The Children's Hospital at Westmead, Westmead, Australia; Metabolism and Obesity Services, Royal Prince Alfred Hospital, Camperdown, Australia; and the Queensland University of Technology, Kelvin Grove, Australia.
2 Supported by the Children's Hospital Fund and the James Fairfax Institute.
3 Reprints not available. Address correspondence to LA Baur, Department of Paediatrics and Child Health, Locked Bag 4001, The Children's Hospital at Westmead, Westmead NSW 2145, Australia. E-mail: louiseb3{at}chw.edu.au.
| ABSTRACT |
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Objective: We sought to both compare measurements of energy intake (EI) from diet records and of total energy expenditure (TEE) by the doubly labeled water (DLW) method and to investigate misreporting of EI.
Design: Forty-seven children (22 boys and 25 girls) aged 7.4 ± 0.8 y (
± SD) were recruited from 25 schools in western Sydney. TEE was measured by DLW over 10 d and EI by use of 3-d food records. Misreporting was defined as [(EI - TEE)/TEE] x 100%.
Results: Girls had a higher (P = 0.02) percentage of body fat (28.2 ± 7.0%) than did boys (22.9 ± 8.0%); otherwise there were no differences among sex. Although mean (±SD) values for EI (7514 ± 1260 kJ/d) and TEE (7396 ± 1281 kJ/d) were not significantly different, there was no significant correlation between EI and TEE. EI and TEE were 9% and 11% lower, respectively, than current World Health Organization recommendations for EI. The relative bias (mean difference, EI - TEE) was low at 118 kJ/d, but the limits of agreement (bias ± 2 SD of the difference) were wide at 118 ± 3345 kJ/d. Although the mean percentage of misreporting was low (4 ± 23%), the high SD indicates large intraindividual differences between EI and TEE. The most significant predictor of misreporting was dietary fat intake (r2 = 0.45, P < 0.0001). Misreporting was not associated with sex or body composition.
Conclusions: In this age group, reported EI is not representative of TEE at the individual level. However, at the population level, 3-d food records may be used for surveys of EI by 69-y-old children.
Key Words: Food record dietary energy intake doubly labeled water energy expenditure children misreporting macronutrients dietary fat Sydney Australia
| INTRODUCTION |
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Misreporting of dietary EI can be defined as the difference between EI (computed from food records) and TEE (estimated from the DLW method) as a percentage of TEE (11). Underreporting and overreporting may be due to either eating more or less than one's habitual intake during the period of the food record or failing to record accurately all foods consumed, either deliberately or because of forgetfulness. Mistakes can be also made in identifying types of food and in estimating portion sizes of foods consumed.
Although many studies have been conducted to validate EI and investigate misreporting in adults, few such studies have been conducted in children. Accuracy of food intake records in children may vary depending on age, developmental stage, and whether the food consumed is recorded by a parent or child. In studies of children and adolescents aged between 1 and 18 y in the United States, United Kingdom, and Sweden, both underreporting and good agreement of EI and TEE estimated by DLW were observed through the use of diet records (25, 7, 12).
Results from the small number of studies in children aged <10 y indicate that diet history, diet recalls, and food frequency questionnaires tend to overestimate EI, whereas diet records (weighed or measured) either underestimate or are in good agreement with TEE by DLW (17, 12, 13). However, validation studies of EI are limited in children aged 69 y. This age is of particular interest because it is a time when physical activity and eating patterns change as children become established in their school schedules and in other routines of middle childhood. To our knowledge, only 2 studies have been conducted that compared EI from diet records with TEE from DLW in children aged 69 y: one study with 12 subjects (aged 7 y) and another study that was restricted to only girls (n = 14, aged 8 y) (4, 7). Several studies, mostly in younger children, showed that measures of TEE by DLW are lower than current recommendations for EI (1418). However, few such studies have been conducted in children aged 69 y. Therefore, the aims of the present study were to compare the level of agreement between reported EI and estimates of TEE by DLW and to investigate misreporting of EI in a group of Australian children aged 69 y.
| SUBJECTS AND METHODS |
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Subjects were recruited from state primary schools in western Sydney. All schools within a 10-km radius of the study center, an area that covers a wide range of persons of different socioeconomic status, were contacted by letter. With the approval of school principals, information was then distributed through the school systems to parents, inviting them to have their child participate in the study. Interested parents contacted us directly and children were recruited from 25 schools within the 10 km radius. Children with any chronic illness other than asthma, or those with acute illness at the time of study were not recruited. During the time of the study no children were taking medications, such as ß2 agonists or methylphenidate, that could have affected the results.
The study protocol was explained to both parents and children, and informed written consent was obtained from a parent. The study was approved by the Human Ethics Committee of The Children's Hospital at Westmead, and the New South Wales Department of Education and Training gave approval for children to be recruited through state schools.
Protocol
Children attended the study center (James Fairfax Institute of Paediatric Nutrition at The Children's Hospital at Westmead) after school or during school holidays. The subjects were studied between June 1998 and February 1999. At this visit, the study protocol was explained, anthropometric measurements were taken, and the doubly labeled water dose was given as explained in detail below.
Anthropometric measurements
Anthropometric measurements were made by using standardized techniques. Standing stretched height (±0.1 cm) was measured by using a Harpenden stadiometer (Holtain Ltd, Crymmych, United Kingdom). Body weight (±0.01 kg) in was measured by using digital scales while subjects wore light clothing. Body mass index (BMI) was calculated as weight/height2 (kg/m2).0
The heights, weights, BMIs, and ages of the subjects in our study were compared with those of a recent, well-sampled population of Australian schoolchildren (The Health of Young Victorians Study; 20) and with the National Center for Health Statistics (NCHS) reference population (21, 22). These measurements were normalized by being expressed as SD (z) scores (22, 23).
Total energy expenditure
TEE was measured over a period of 10 d by using the DLW method. A baseline urine sample was collected before subjects were given an oral dose of DLW (0.05 g 2H2O/kg and 0.125 g H218O/kg) from a flask by use of a drinking straw. The flask was weighed before and after dosing to determine the actual dose of DLW administered. Isotopes were sourced from CK Gas Products Ltd, Berkshire, United Kingdom (H218O) and the Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia (2H2O). At home, subjects collected a urine sample 36 h postdose and then once daily for the next 10 d. Samples were frozen until collected by a research assistant at the end of the collection period. Samples were analyzed for 2H2O and H218O by isotope ratio mass spectrometry in the energy metabolism laboratory at the Queensland University of Technology. The technique has been described in detail elsewhere (12, 24). In brief, the multipoint approach was used with an assumed respiratory quotient over the 10-d period of 0.85. In subjects with a zero energy balance and zero or minimal growth over a period of days, TEE would also be equal to total EI. In the age range of children in this study, the energy stored in new tissue (ie, growth) would be a very small proportion (
2%) of total EI.
Measurement of body composition
Fat-free mass measures were derived from the 18O dilution space under the assumption that this was 1% larger than total body water and by using the appropriate value for the hydration of fat-free mass in children of different ages (25). Fat mass was calculated as the difference between body weight and fat-free mass. Percentage of body fat was calculated by using fat mass and body weight measurements.
Resting energy expenditure
Anthropometric, TEE, and body-composition measurements were taken in the afterschool period and it was therefore not possible to determine resting energy expenditure (REE) of each subject in the fasted state. It has been shown in our facility, and those of others, that there is good agreement between REE of prepubertal children measured by indirect calorimetry and REE predicted by the Schofield equations (2628). For example, Firouzbakhsh et al (27) directly measured REE in 199 healthy children aged 516 y and found good agreement between measured REE and REE predicted by the Schofield equations. The Schofield equations have been widely used to predict REE in many studies in children (2931). We therefore calculated predicted REE for each subject by using the Schofield equations (28), which are based on body weight, age, and sex. Physical activity level was defined as the ratio of TEE to REE.
Energy intake
The dietary intake record was explained to parents at the time of their visit to the study center. With assistance from their child, parents were asked to record their child's food and drink intake for 3 consecutive days, including 1 weekend day. Parents were asked to inform caretakers to document details of meals and snacks that were eaten by subjects when they were either away from home or in the absence of parents, for example, during afterschool care. Household measures (eg, metric cup and spoons) were used to describe quantities of food items when possible. Instructions were given on how to record cooking methods, brand names of foods, and recipes used. Parents were asked to submit family recipes of any meals that had been made and consumed from such recipes during the record period. A booklet in which to record food and drink intake was provided, in addition to a sample of a completed record and metric measuring cups and spoons. A phone call was made to parents during the days the record was kept to discuss any problems, and a dietitian reviewed the food record upon completion. Further details and clarification of food items were obtained by phone calls to parents when necessary. Food records were analyzed using the DIET 1.0, version 4.0, computer program (Xyris Software, Highgate Hill, Australia), which is based on a database of Australian foods (32).
Goldberg's cutoffs for dietary records
Minimum cutoffs for habitual energy expenditure below which a healthy adult could not live a normal sedentary lifestyle have been established to evaluate EI data (33). The Goldberg tabulated cutoff limits identify minimum plausible levels of energy expenditure expressed as a multiple of REE (33). Although these cutoffs were developed for adults, they have been adopted for use in children (34) and we used them as a screening tool to detect those records likely to be false reflections of EI.
A ratio of EI:REE of 1.06 is the Goldberg cutoff to test whether EI reported from a 3-d diet record is a plausible measure of the food consumed during the actual measurement of dietary intake (33). In the current study, the mean ratio of EI:REE was 1.72 ± 0.24 (range: 1.262.26). Therefore, according to the appropriate Goldberg cutoff, no food records needed to be discarded due to failure by parents to record a significant proportion of their child's dietary intake.
Statistical analysis
Data were analyzed using SPSS for WINDOWS release 8.01 (SPSS Inc, Chicago). Data are expressed as means ± SDs. One-way analysis of variance was used to examine sex differences in physical characteristics, reported EI, measured TEE, misreporting, and reported macronutrient intake. Misreporting was defined as [(EI- TEE)/TEE] x 100%. This ratio was used to indicate the magnitude of the difference between EI and TEE in relation to the subject's average daily energy expenditure measured by use of DLW (11).
Student's t test was used to investigate the differences between children's height, weight, and BMI z scores and the NCHS reference population median. A nonparametric test (Mann-Whitney U test) was used to compare age, height, weight, and BMI of children in our study (n = 47) with those of children in the Health of Young Victorians Study (n
200; 20) because of the unequal number of subjects participating in the 2 studies. Reported EI and TEE data were analyzed by using the Bland and Altman technique for assessing agreement between 2 methods of measurement (35). Correlation was used to determine the level of association between variables. Linear regression was used to investigate relations between reported EI and measured TEE. Standard multiple linear regression techniques were used to develop a model that predicted the level of misreporting. P values < 0.05 were considered significant.
| RESULTS |
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Energy intake data
Reported macronutrient intake and percentage of energy from protein, carbohydrate, and fat are shown in Table 2
. There were no significant differences between boys and girls in macronutrient intake except that boys had a higher protein intake and percentage of energy from protein (70 ± 15 g/d and 16 ± 2% in boys compared with 61 ± 13 g/d and 14 ± 2% in girls).
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Comparison of reported energy intake and measured energy expenditure
In the total group, mean EI and TEE were 7514 ± 1260 and 7396 ± 1281 kJ/d, respectively (Table 2
). However, there was no significant relation between reported EI and measured TEE (r = 0.10, P = 0.51). A scatter plot of the mean daily total EI compared with the mean daily TEE for all subjects is shown in Figure 1 . The mean ratio of EI:TEE was 1.04 ± 0.23, which was not significantly different from 1.00.
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| DISCUSSION |
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Children were recruited from a large number of schools. This may have inevitably been a biased sample of highly motivated parents and children, given the demands of the study, such as attendance at the study center, keeping of a 3-d diet record, and daily, timed urine collection over 10 d. Nevertheless, accuracy should be greater with well-motivated parents recording their child's EI. Our decision to use a 3-d diet record rather than a longer period of recording was based on the practical consideration that it is unreasonable to expect even highly motivated parents to record their child's EI for longer periods. In addition, because accurate food intake recording is very time consuming and requires recall of often complex daily events, the longer the time period of the food record, the greater the risk of mistakes, whether deliberate or unintentional.
Mean values for TEE and reported EI were similar in our study, and consequently the mean level of misreporting was low. Despite this, there were some large intraindividual differences between these 2 measures as evidenced by the wide range of the limits of agreement (-3226 and 3462 kJ/d) and the high SD for mean misreporting (23%), consistent with similar studies in children who were both younger and older than those in the present study (7, 13).
There are several explanations for these discrepant observations. First, it is possible that subjects were undereating or overeating during the period of the 3-d diet record, although subjects could still have been in energy balance over the 10-d period of the DLW study. Because of practical difficulties, we did not weigh the children at the end of the DLW study to detect whether they had been in energy balance; we recommend that future studies address this issue. In a study of obese adult men, most of whom underreported their EI, Goris et al (11) showed that total underreporting of EI could be explained by undereating as well as failure to record all food consumed.
A second possible explanation for the discrepancies between reported EI and measured TEE lies in the varied lifestyle patterns of children. For example, even for highly motivated parents, it is less easy to record accurately all foods eaten by more active children who are away from home for long periods during their various activities. Future validation studies of EI in children should include an independent measure of physical activity so that appropriate adjustments can be made. When evaluating EI from food records, one of the limitations of using the Goldberg cutoffs is that they are not adjusted for different levels of physical activity. Although our study was not designed to independently measure physical activity, we did find a significant inverse relationship between misreporting and physical activity level. However, although this result was significant, it would be expected from the definition of misreporting [(EI - TEE)/TEE x 100%] and of physical activity level (TEE/REE) that if TEE increases, physical activity level increases while the percentage of misreporting decreases, thus resulting in an inverse relation between these 2 variables. Clearly, the relation between a child's reported dietary EI and physical activity requires further investigation.
A third possible explanation for the individual discrepancies between reported EI and measured TEE is that the underrecording or overrecording of a child's dietary intake by parents may be deliberate or unintentional. In Western society, there is a high degree of sensitivity about personal information, such as food intake, and an awareness that individuals are judged on the type and amount of food they eat. McDiarmid et al (40) showed that adults who were found to underreport their food intake admitted in a subsequent interview that their food records were not representative of their habitual intake. Similarly, parents may be embarrassed about the type or amount of food that their children eat and may offer them what they consider to be healthy foods during the period of the food record or deliberately not record foods that were eaten (underrecording). In addition, although parents may accurately record their child's EI at home, if their child spends a significant amount of time in activities under the supervision of other adults, parents must rely on reports of EI either from their child or from other adult caretakers who may not be as committed to the study.
Consistent with findings in adults, our study showed that a higher reported fat intake was associated with a tendency to overestimate EI (41). However this finding would be expected from the definition of misreporting because increased consumption of fat, an energy dense macronutrient, is related to greater EI and hence a higher degree of overreporting.
Fifty-five percent of children in the current study had reported EI higher than TEE, indicating that there was a slight bias toward overreporting. In addition, there was no relationship between misreporting and either age, sex, BMI, BMI z score, weight, weight z score, or percentage of body fat. These results are contrary to those reported in adults showing that EI by weighed diet record is biased toward underestimation of habitual intake, especially in heavier individuals (11, 42). The influence of parental adiposity on misreporting of EI in children has yielded inconsistent results and this complex area requires further investigation (4, 13, 43). Studies in older children (aged 10 y) and adolescents have shown a positive association, similar to that found in adults, between underreporting and a tendency toward greater body fatness and body weight (2, 3, 7). There are many possible reasons for the difference in the determinants of misreporting between the current study and those in older subjects. For the young children in our study, EI was recorded by parents, whereas older children, adolescents, and adults take the responsibility for recording their own food intake. Issues pertaining to body image and current dieting behavior become more important influences in the lives of older children and could therefore affect the accuracy of self-reported food records, as was shown in adult studies (44, 45).
The results of the present study and the existing EI studies in younger children (aged 19 y) suggest less misreporting of dietary EI than in older children and adolescents (3, 4, 7, 12). A possible explanation is that in younger children, there is more parental control and supervision of food intake and therefore the parent can more accurately report the child's EI. In contrast, in older children who normally self-report their EI, there is a tendency toward more unstructured eating patterns and eating away from home, leading to a greater degree of forgetfulness and thus, underestimation of EI. Although misreporting appears to be age-related, we minimized this effect in our study by selecting prepubertal children in a tight age range (69 y).
The children and parents in our study were reasonably representative of the Australian population and hence our findings are likely generalizable to other westernized societies. The use of TEE from DLW as an independent marker of food intake in the present study has shown that, at the individual level, 3-d food records lack precision. However, our findings of a low mean level of 4% of misreporting for the total group suggest that 3 d food records may be used for population surveys of EI in schoolchildren aged 69 y.
| ACKNOWLEDGMENTS |
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