Supermarket Transaction Records In Dietary Evaluation – The STRIDE study: validation against self-reported dietary intake

Abstract Objective: Scalable methods are required for population dietary monitoring. The STRIDE study compares dietary estimates from supermarket transactions with an online Food Frequency Questionnaire. Design: Participants were recruited in four waves, accounting for seasonal dietary variation. Purchases were collected for one year during and one year prior to the study. Bland-Altman agreement and limits of agreement were calculated for energy, sugar, fat, saturated fat, protein and sodium (absolute and relative). Setting: This study was partnered with a large UK retailer. Participants: 1,788 participants from four UK regions were recruited from the retailer’s loyalty card customer database, according to breadth and frequency of purchases. 686 participants were included for analysis. Results: The analysis sample were mostly female (72%), with a mean age of 56 years (SD 13). The ratio of purchases to intakes varied depending on amounts purchased and consumed; purchases under-estimated intakes for smaller amounts on average, but over-estimated for larger amounts. For absolute measures, the limits of agreement across households were wide, e.g. for energy intake of 2000kcal, purchases could under or over-estimate intake by a factor of 5; values could be between 400kcal to 10000kcal. Limits of agreement for relative (energy-adjusted) estimates were smaller, e.g. for 14% of total energy from saturated fat, purchase estimates may be between 7% and 27%. Conclusions: Agreement between purchases and intake was highly variable; strongest for smaller loyal households, and for relative values. For some customers, relative nutrient purchases are a reasonable proxy for dietary composition indicating utility in population-level dietary research