Development and validation of an online portion size norm assessment tool

Abstract

Abstract Background Portion size norms (described as a typical perception of how much of a given food individuals choose to eat in one eating occasion) may have shifted towards larger sizes due to the high availability of large package and serving sizes. This is especially concerning for discretionary foods that are energy-dense and nutrient-poor. Currently, there is a lack of validated tools to assess portion size norms for common foods. Therefore, the aim of this study was to develop and validate an online image-based tool to examine the portion size norms of discretionary foods among Australian consumers. Methods Using a within-person crossover design, an online survey with image-series of 15 discretionary foods and drinks was validated against corresponding real foods. Participants selected their normal portion size using both methods and could choose from a scale ranging from 0 (do not eat this food) to 9 (greater than the largest option displayed). Agreement between methods was examined using cross-classification and intra-class correlation coefficient (ICC). Results A sample of 114 Australian adults were recruited (mean age 24.8 years). Cross classification indicated over 90% of selections (ranging from 86-96%) were matched in the same or adjacent portion size option. ICC was 0.85 across all foods, and 12 of the 15 foods demonstrated a good to excellent level of agreement (ICC >0.75). Conclusion This novel food images survey showed good agreement when compared with corresponding real foods. This survey may be a valuable tool to examine portion size norms for common discretionary foods among Australian adults in future studies.