Development and validation of a food photography atlas for portion size estimation of traditional Croatian dishes in adults

Background Accurate portion size estimation is an important component of dietary assessment. Food photography atlases, which are among the most commonly used portion size measurement aids, are designed to take into account the cultural context and dietary patterns of the target population. Therefore, the aim of this study was to develop and validate food photography atlas of traditional Croatian dishes for adults. Methods The 30 dishes were selected, in accordance with the gastronomic regions defined by Croatian National Tourist Board. The portion sizes were determined using data from the first Croatian national food consumption survey of the adult population, conducted in accordance with the EU Menu methodology. The photographs were validated by comparing them with the actual dishes served to 110 participants over a three-day period. Validity assessment included mean differences between actual and estimated portion sizes using the Wilcoxon signed-rank test, correlations between actual and estimated portion sizes, Bland– Altman limits of agreement, and quadratic weighted Cohen’s kappa. Results Of the 30 selected traditional dishes, no significant differences between actual and estimated portion sizes were observed for 46.7% of dishes, whereas portion sizes were underestimated for 30% and overestimated for 23.3%. For half of the dishes, at least 50% of the estimates were within ±10% of the differences between actual and estimated portion size. Spearman’s correlation showed a strong association between actual and estimated portion size for all 30 dishes. Bland–Altman analysis demonstrated good agreement between actual and estimated portion sizes, with low systematic bias and narrow limits of agreement for single-unit and countable dishes. In 66.7% of dishes, more than half of the estimations were correct, while across all 30 dishes the proportion of distant estimations ranged from 0.0 to 31.0%. Quadratic weighted Cohen’s kappa indicated almost perfect agreement for 29 dishes and substantial agreement for one dish. Conclusion These results support the validity of the food photography atlas for estimating portion sizes of traditional dishes among adults in Croatia.