Silvia Maria Voci

Reproducibility of a food frequency questionnaire for adolescents

To assess the reproducibility of a validated 76-item food frequency questionnaire designed to estimate diet in adolescents (Adolescent Food Frequency Questionnaire--AFFQ) in the city of Sao Paulo, Brazil, a test-retest study was conducted (n = 49). Intraclass correlation coefficient (ICC), weighted kappa, and percentage of agreement were used in both crude and energy-adjusted nutrient intakes. Bland Altman plots were used to examine the limits of agreement for energy and macronutrients. The ICC ranged from 0.48 (carbohydrates) to 0.65 (vitamin C) in crude values and from 0.25 (total fat) to 0.58 (vitamin C) in adjusted values. Kappa values ranged from 0.28 (protein and fiber) to 0.56 (unsaturated fat). Bland Altman showed a trend towards larger difference in energy according to increased intake values and a bias towards extreme values for fat intake. The percent of individuals classified in the same category on the two occasions was on average 54.2%. By conclusion, the Adolescent Food Frequency Questionnaire showed reasonable reproducibility and can be used in studies that aim to classify groups into intake categories.

Validação do Questionário de Freqüência Alimentar para Adolescentes (QFAA) por grupos de alimentos em uma população de escolares

OBJETIVO: Verificar a validade do Questionario de Frequencia Alimentar para Adolescentes para avaliar o consumo de grupos de alimentos entre escolares de Piracicaba, Sao Paulo. METODOS: Participaram do estudo 94 adolescentes, com idade entre 11 e 15 anos, matriculados em uma escola da rede publica. O consumo alimentar foi avaliado pelo Questionario de Frequencia Alimentar para Adolescentes (QFAA) e a media de dois Recordatorios de 24 horas (R24h) foi utilizada como metodo de referencia. Os itens alimentares foram classificados em 18 grupos. Foram realizadas analises descritivas, teste t-Student pareado e de Wilcoxon, coeficientes de correlacao de Pearson e de Spearman. Foram tambem utilizadas analise de quartis e estatistica Kappa ponderado. Os coeficientes de correlacao foram corrigidos pela variância intrapessoal dos R24h, estimada a partir de ANOVA com um fator de classificacao. RESULTADOS: Nao foram verificadas diferencas significativas entre os instrumentos para o arroz, massas, carnes, refrigerantes e sucos artificiais. Os coeficientes de correlacao corrigidos pela variabilidade intrapessoal variaram de -0,26 a 0,78. A concordância de classificacao dos individuos no mesmo quartil de consumo para ambos os metodos variou de 22% (massas) a 50% (feijao). Para quartis opostos, os grupos que tiveram mais de 10% dos individuos classificados incorretamente foram massas (19%), carnes (13%) e gorduras (11%). Os valores de Kappa ponderado variaram de - 0,15 (massas) a 0,56 (feijao). O QFAA superestimou o consumo de quase a totalidade dos grupos alimentares e subestimou os grupos dos oleos, feijao, carnes e refrigerantes. CONCLUSAO: O instrumento apresentou boa validade para feijao, verduras e legumes, leite e derivados, biscoitos recheados e para o arroz.

Validation of a food frequency questionnaire to assess the consumption of carotenoids, fruits and vegetables among adolescents: the method of triads

The aim of this study was to validate the intake of carotenoids, fruits and vegetables estimated by the Food Frequency Questionnaire for Adolescents (FFQA) using the method of triads. Blood samples were collected from 80 elementary school adolescents to assess serum levels of β-carotene. Partial correlation coefficients (r) were calculated between an estimated intake of carotenoids, fruits and vegetables and the serum levels of β-carotene. Validity coefficients were calculated using the method of triads. With the exception of carotenoids, partial r from the food frequency questionnaire (FFQ) were greater than those of the 24-hour recall (24hR). The fruit/vegetable group showed the highest partial r for the FFQ (r = 0.235) and the 24hR (r = 0.137). The highest validity coefficient was obtained for the vegetable group, as assessed by the FFQ (r = 0.873). On average, the validity coefficient values for the FFQ were greater than those obtained for the 24hR or the β-carotene serum levels. The FFQA is an accurate tool for estimating the intake of carotenoids, fruits and vegetables in this population group.

Use of linear regression for correction of dietary data

OBJECTIVE Methodological approaches have been developed to minimize effects of measurement error in dietary intake data. The objective of the study was to apply a strategy to correct intake data according to measurement error. METHODS Intake data were obtained by applying the Food Frequency Questionnaire in 79 adolescents of São Paulo city, Brazil. Correction of dietary intake data was performed by linear regression, after energy adjustment by the residual method. The reference method used was 24-hour dietary recall and it was applied three times. RESULTS Corrected values were similar to reference values. Correction factor gamma was 0.89 to energy. For macronutrients, factors were 0.41, carbohydrate 0.22, and lipid and protein 0.20. CONCLUSIONS Mean and standard deviation of corrected values show a correction for the measurement error. The performance of these methods, that are imperfect, is questioned when the assumptions are not proved which is common in intake studies of measures based on the reports of individuals.

Estudo de calibração do Questionário de Frequência Alimentar para Adolescentes (QFAA)

In order to establish calibration factors of the Adolescent Food Frequency Questionnaire (AFFQ), 74 boys and girls from Piracicaba (SP, Brazil) with ages ranging from 10 to 14 took part in the study. Dietary intake (assessed by the food frequency questionnaire and 24-hour recall) was assessed and adjusted for energy intake. Descriptive statistics, variance analysis using one classification factor, Pearsons correlation coefficients and linear regression were performed. The average of two 24-hour recalls was used as a reference for calibration of data. Calibration coefficients (λ) ranged from -0.07 (iron) to 0.40 (vitamin C) revealing substantial error in the dietary method tested, albeit similar to those observed in the literature. As these coefficients were low, they indicate the need for reformulating the instrument regarding some nutrients, though application was not considered advisable for correcting information on iron and retinol. The methodology used to calibrate dietary data can consider measurement error in the assessment when its assumptions are respected, since violations of these assumptions may lead to other errors that are difficult to predict.

Within- and between-person variations as determinant factors to calculate the number of observations to estimate usual dietary intake of adolescents

This cross-sectional study describes the variation in the dietary intake of energy and macronutrients based on estimated coefficients of within- and between-person variation and intends to calculate the number of days required to evaluate the dietary intake of adolescents in Piracicaba, Brazil. The sample was made up by ninety-two adolescents aged between eleven and sixteen years. Interviews were performed to assess demographic, anthropometric and dietary variables, which were evaluated by the answers obtained through two 24-hour recalls. Descriptive analyses were performed and variances and Coefficients of variation within- and between-person were obtained by results of one-way ANOVA. The mean energy intake observed was 2,326.2 kilocalories; mean macronutrient intake came to 89.0 grams of fatty acids, 305.3 grams of carbohydrates and 82.2 grams of proteins. Coefficients of within-person variation ranged from 36% to 45%, while between-person coefficients varied from 26% to 31%. Variance ratios ranged from 1.35 (carbohydrate) to 2.62 (protein). The lowest number of observations required to correctly evaluate the usual diet calculated (r = 0.90) was six days, for carbohydrates while the highest was eleven, for proteins. Coefficients of variation were similar to those observed in international studies. We conclude that, in this study, two observations were sufficient to obtain reasonable correlations. However, six evaluations are necessary for these adolescents in order to obtain excellent correlations.

Validity and reliability of self-reported weight and height measures for the diagnoses of adolescent's nutritional status

PURPOSE: To assess the validity and reliability of self-reported height, weight, and Body Mass Index (BMI) to diagnose the nutritional status of adolescents. METHODS: The study included 360 public school students of both genders, with ages ranging from 10 to 15 years. Adolescents self-reported their weight and height, and these values were later obtained directly by interviewers. The validity of BMI based on self-reported measures was calculated using sensitivity and specificity indexes, and positive predictive value (PPV). Agreement between self-reported and measured BMI was evaluated using Kappas weight coefficient, the Lin correlation coefficient, and Bland-Altman and Lins plots. RESULTS: Both girls and boys underestimated their weight (-1.0 girls and boys) and height (girls - 1.2 and boys - 0.8) (p < 0.001). BMI presented moderate agreement between measured and self-reported values. Sensitivity of estimated BMI based on reported measures to classify obese subjects was higher for boys (87.5%) than it was for girls (60.9%), whereas specificity was higher for girls (92.7%) than it was for boys (80.6%). PPV was high only for classification of normal-weight adolescents. CONCLUSIONS: Self-reported measures of weight and height in adolescents do not present valid measures; therefore, they should not be used to replace measured values. Additionally, we observed that 10% of obese boys and 40% of obese girls could have remained unidentified if we had used only self-reported measures, emphasizing the effects of the low reliability of self-reporting.

Estimativa de valores corrigidos e o efeito da correção pelo erro de medida em dados dietéticos obtidos por Questionário de Frequência Alimentar para Adolescentes (QFAA)

The scope of this study was to estimate calibrated values for dietary data obtained by the Food Frequency Questionnaire for Adolescents (FFQA) and illustrate the effect of this approach on food consumption data. The adolescents were assessed on two occasions, with an average interval of twelve months. In 2004, 393 adolescents participated, and 289 were then reassessed in 2005. Dietary data obtained by the FFQA were calibrated using the regression coefficients estimated from the average of two 24-hour recalls (24HR) of the subsample. The calibrated values were similar to the the 24HR reference measurement in the subsample. In 2004 and 2005 a significant difference was observed between the average consumption levels of the FFQA before and after calibration for all nutrients. With the use of calibrated data the proportion of schoolchildren who had fiber intake below the recommended level increased. Therefore, it is seen that calibrated data can be used to obtain adjusted associations due to reclassification of subjects within the predetermined categories.