Development and validation of a photographic food atlas for portion size estimation in Singapore

Accurate portion size estimation is essential for dietary assessment, yet existing food atlases have limited applicability in Singapore due to its multi-ethnic culinary heritage and unique dietary patterns. This study describes the development and validation of the first comprehensive photographic food atlas designed specifically for Singapore.

The atlas was developed using two primary data sources, the 2021 Health Promotion Board Energy and Nutrient Composition of Food database and 24-h dietary recall survey from Singapore's 1st Total Diet Study, to ensure representativeness of commonly consumed foods. Following systematic exclusion criteria, 298 atlas entries were included, representing foods in specific forms or presentations. Of these, 67 entries were series photographs and 231 entries were guide photographs. Validation involved 41 adult participants, recruited through convenience sampling from the national reference laboratory for food science. Participants evaluated 14 entries presented as photo series by selecting the images that best matched corresponding pre-weighed food portions, with two different portions tested per entry. Accuracy was assessed using mean differences, standard deviations, quadratic weighted kappa coefficients, and Spearman coefficients between selected and actual photograph numbers. Additional usability evaluation and participant feedback were also collected.

Of the 14 entries tested, 11 (78.6%) met the predefined validation criteria (mean difference < |0.3| and standard deviation < 1). Three entries (beef, peanut, and fish) showed underestimation. Quadratic weighted kappa coefficients ranged from 0.23 to 0.96, while Spearman coefficients ranged from 0.44 to 0.96. Most entries demonstrated good agreement and strong rank-order association. The proportion of correct responses decreased as portion size increased (96.7% for small portions vs. 42.4% for extra-large portions). Most participants rated the atlas favourably for representativeness (76%), portion size appropriateness (73%), and confidence in using the atlas for portion size estimation (71%).

This first comprehensive photographic food atlas for Singapore comprises 298 entries of commonly consumed foods. Preliminary validation of 14 selected series entries demonstrated satisfactory accuracy, identifying areas for future refinement, particularly regarding presentation methods for certain entries. Overall, the study demonstrates that the atlas can be useful as a practical, localised tool to support dietary assessment of relevant foods in research and policy.