Accuracy of estimates of food portion size using food photographs--the importance of using age-appropriate tools.

BACKGROUND: In order to obtain a measure of nutrient intake, a measure or estimate of the amount of food consumed is required. Weighing foods imposes a large burden on subjects, often resulting in underreporting. Tools are available to assist subjects in providing an estimate of portion size and these include food photographs. The application of these tools in improving portion size estimation by children has not been investigated systematically.
OBJECTIVES: To assess the accuracy with which children are able to estimate food portion sizes using food photographs designed for use with adults, and to determine whether the accuracy of estimates is improved when age-appropriate portion size photographs are provided.
DESIGN: Original data from three separate studies, on the accuracy of portion size estimates by adults using food photographs, by children using adult photographs and by children using age-appropriate photographs, are analysed and compared.
SUBJECTS: One hundred and thirty-five adults aged 18 to 90 years and 210 children aged 4 to 11 years.
RESULTS: Children's estimates of portion sizes using age-appropriate food photographs were significantly more accurate (an underestimate of 1% on average) than estimates using photographs designed for use with adults (an overestimate of 45% on average). Accuracy of children's estimates of portion size using age-appropriate photographs was not significantly different from that of adults. Children overestimated a food's weight by 18% on average and adults underestimated by 5%.
CONCLUSIONS: Providing children with food photographs depicting age-appropriate portion sizes greatly increases the accuracy of portion size estimates compared with estimates using photographs designed for use with adults.