Assumptions About Portion Size Measurement Aids

Purpose: Portion size measurement aids (PSMAs) are used extensively by dietitians. In this cross-sectional, descriptive study, we explored the degree of consistency and concordance between measured and putative volumes of selected household and sport-related PSMAs that are commonly used for nutrition education and dietary assessment. Methods: An online search of portion size resources yielded several governmental and academic descriptions of household PMSAs (e.g., a compact disc, a nine-volt battery) and sportrelated PMSAs (e.g., a golf ball) and their purported dimensions. The spherical items were purchased locally and measured using electronic digital calipers; measurements were then converted to volumes, in millilitres. Results: Overall, we observed a high degree of heterogeneity in how different educational resources related sport-related PSMAs to portion sizes of food. The mean percentage of error between the measured and putative volumes of PSMAs varied considerably. Conclusions: Our findings indicate that the inaccurate use of PSMAs can lead to systematic bias in nutrition education and misreporting of dietary intake during dietary assessment. Dietitians should exercise caution when using PSMAs because these may not reflect the true portion size they are meant to represent.