Dietary assessment in the 1993 Pelotas (Brazil) birth cohort study: comparing energy intake with energy expenditure Avaliação dietética da coorte de nascimentos

The study aims to describe and compare two methods of energy intake assessment and one measure of energy expenditure applied in adolescents from a birth cohort. In a sub-sample of the 1993 Pelotas (Brazil) birth cohort, followed up in 2006-7, information on intake was obtained through a food-frequency questionnaire (FFQ) and three 24-hour-recalls (24hR), while energy expenditure was assessed using an accelerometer. Bland & Altman plots were used in the analyses in order to compare the methods. The mean difference between FFQ and 24hR was 592 ± 929cal/day. Compared to energy expenditure, intake was overestimated when measured by FFQ (357 ± 968cal/day) and underestimated by 24hR (-278 ± 714cal/day). In spite of the great differences between energy intake obtained using the two methods, lower differences were observed when these methods were compared to expenditure. Energy Intake; Adolescent Nutrition; Energy Metabolism; Validation Studies Introduction A challenge in nutritional epidemiology is to measure accurately food intake. Different methods are used in dietary assessment, but errors are inherent in all of these methods 1. In epidemiology, the process used to assess measurement errors is known as validity. A measure is valid or accurate if the figure found is close to the true value. In nutritional epidemiology, however, this process is challenging, because it is unlikely that a single instrument will provide “gold standard” information on the intake of foods or nutrients. Comparisons among different methods of dietary assessment, including reliability and reproducibility of measurements, have been conducted in several studies, mainly from high income countries, and summarized in review studies 2,3. The conclusion of all these studies is that each method presents a margin of bias and none may be considered as a gold standard. In addition, while some methods investigate food intake over a one-day period, others assess the usual intake of foods. So, the validation process of energy intake has been compared using external methods such as: (a) energy required maintaining weight; (b) measured energy expenditure; (c) presumed energy requirements, expressed as multiples of basal metabolic rate. The three comparison methods are based on the assumption that energy intake is equal to energy expenditure when weight is stable. To sum up, 2080 ARTIGO ARTICLE DIETARY ASSESSMENT IN THE 1993 PELOTAS BIRTH COHORT 2081 Cad. Saúde Pública, Rio de Janeiro, 26(11):2080-2089, nov, 2010 the validation process of energy intake should include different methods of dietary assessment and other techniques such as external measurements or biomarkers 3. The direct comparison of energy intake and expenditure allows the assessment of measurement errors and the doubly labeled water (DLW) technique has been considered as a gold standard for measuring energy expenditure under realistic daily conditions. Given that DLW is expensive and only available to a few research centers, alternative methods for measuring energy expenditure (heart-rate monitoring, accelerometers or physical activity questionnaires) may also be used to validate reported energy intake. Considering the limitation of reported physical activity through questionnaires and the high cost of DLW, accelerometry has become the method of choice for objectively measuring physical activity in free-living adolescents 4, taking into account that the accelerometer shows reasonable concordance with DLW for measuring daily energy expenditure 5. In the present study, the main objective is to describe and compare two methods of energy intake assessment and one measure of energy expenditure applied in adolescents from a birth cohort study. Energy intake estimated from two instruments is compared with energy expenditure measured by accelerometry.