Longitudinal stability of dietary intake patterns in pediatric-onset multiple sclerosis: A multicenter prospective cohort study

BACKGROUND: Diet may influence MS activity, but most studies use a single dietary measure. The stability of diet over time in pediatric-onset MS (POMS) is unclear. OBJECTIVES: To evaluate the reproducibility and short-term temporal stability of dietary intake in youth with POMS using repeated food frequency questionnaires (FFQ). METHODS: This longitudinal study included participants with a baseline FFQ (the Block Kids Food Screener, 2014). Intraclass correlation coefficients (ICCs) were estimated using random-intercept mixed-effects models to quantify the relative contributions of between-person and within-person variability. Temporal trends in intake were assessed by modeling time since baseline as a fixed effect, using log-transformed dietary variables to estimate percent change over time. RESULTS: Of 419 FFQs from 195 participants, 140 (71.8%) completed ≥2 FFQs over a median of 6.5 months (range 2.8-18). ICCs ranged from 0.41 to 0.78 across dietary measures, with the highest reproducibility observed for vegetables and fiber (ICCs 0.78 and 0.72). Log-transformed models showed small declines in several nutrients over time, corresponding to <10% change over a six-month period. CONCLUSIONS: Dietary intake demonstrated moderate to good reproducibility over the 6 to 18 month follow-up period. Vegetable and fiber intake had the strongest reliability. These findings suggest that reported dietary intake assessed by a single or infrequent FFQ may remain reasonably stable over a 6- to 18-month period in longitudinal POMS studies. However, the moderate-to-good reproducibility observed indicates that within-person variability persists and may attenuate diet-disease associations when only a single dietary assessment is available.