Effect of day-to-day variation in dietary intake on dietary patterns identification through factor analysis

Abstract Background/objectives Short-term dietary assessments, such as 24-h recalls, are affected by day-to-day variation, influencing the stability and identification of dietary patterns through factor analysis. We evaluated the effect of within-person random error on replicating these patterns. Methods Twenty non-consecutive 24-h recalls were completed by 302 adults over about three months. Individual usual intakes were defined as the average of 20 days. Factor analyses identified: (i) usual dietary patterns (20dDP), based on usual individual intakes; and (ii) n -day ( n = 2, 3, or 4) dietary patterns (ndDP), based on all possible recall combinations. Factor mirroring and interchangeability ensured alignment for comparison between 20dDP and ndDP factor loadings distributions. Results Three usual dietary patterns were identified: Prudent, Traditional, and Western, explaining 25% of the variance. Mean loading factors from 190 two-day combinations were weaker than the usual ones, with substantial attenuation in the third factor. Foods in the usual first and second factors were consistently identified in most 2-day combinations. In contrast, foods of the usual third pattern were identified largely by chance, depending on the sampled 2-day combination, and more foods not belonging to this factor were incorrectly assigned. This indicates that while two-day data capture major patterns, subsequent, less explanatory factors are highly susceptible to random error. Results were similar for 3 and 4-day combinations. Conclusions Usual dietary patterns can be identified using at least 2 non-consecutive collection days; however, the first factor is most stable, while subsequent factors show greater susceptibility to day-to-day variation, potentially compromising replication of usual dietary patterns.