Validity of children's food portion estimates: a comparison of 2 measurement aids.

BACKGROUND Policy and clinical decisions regarding children's nutrition are often based on dietary intake estimates from self-reports. The accuracy of these estimates depends on memory of both the type of food eaten and the amount consumed. Although children's self-reports of food intake are widely used, there is little research on their ability to estimate food portions. OBJECTIVE To assess the validity of children's estimates of the food portions they consume by means of 2 types of measurement aids: standard 2-dimensional food portion visuals and manipulative props. DESIGN Randomized controlled trial. PARTICIPANTS Fifty-four African American girls aged 8 to 12 years. MAIN OUTCOME MEASURES Girls were served a standard meal and actual intake was assessed by weighing food portions before and after the meal. On completion of the meal, dietitians collected food recalls and portion size estimates from the girls by means of both manipulative props and 2-dimensional food portion visuals, administered in a randomized order. RESULTS Absolute value percentage differences between actual and estimated grams of food consumed averaged 58.0% (SD, 102.7%) for manipulative props and 32.8% (SD, 72.8%) for 2-dimensional food portion visuals. Spearman correlations between actual and estimated intakes with both portion size measurement aids were high (range, r = 0.56 to 0.79; all P<.001), with the exception of bread intake (r = 0.16, P =.43). Correlations with actual intakes did not differ significantly between the 2 methods. CONCLUSIONS Children's self-reported portion size estimates are appropriate for ranking children's relative intakes, but they result in sizable errors in quantitative estimates of food and energy intakes. Caution should be used in interpreting quantitative dietary intake estimates derived from children's self-reports.