Background: Many epidemiological studies rely on dietary exposures taken from baseline only. This limits our understanding of diet-disease associations because it requires assuming a level of temporal stability, either by individuals or dietary pattern composition. Objectives: This study aimed to evaluate these analytic assumptions of pattern structure consistency and baseline adherence using a cohort of US Black women with repeated measures of food frequency questionnaires (FFQ). Methods: Data from 6151 Black women aged 21-69 from the Black Women's Health Study with complete FFQ data in 1995, 2001, 2013, and 2021 were evaluated for temporal stability. Baseline dietary patterns were derived using an overfitted latent class model. Parameter estimates from the baseline model were then applied to subsequent waves to track individual transitions between existing patterns. Dietary patterns were also derived at each time point using an overfitted latent class model and assessed for changes in pattern composition over time. Results: Five baseline dietary patterns were identified in 1995. Only 18% of participants remained in the same baseline dietary pattern across all four time points, while all others transitioned to a different baseline-derived pattern. Dietary patterns derived independently at subsequent time points, yielded a different number of dietary patterns at each time point (2001: 6 patterns, 2013: 5 patterns, 2021: 4 patterns). Correlation strength of subsequent derived patterns and baseline patterns significantly weakened in strength after 2001 (40% pairings > 0.5), with no patterns correlated greater than 0.5 in 2021. Conclusion: Prospective studies that rely on baseline dietary exposure data cannot assume stability of pattern composition or individual pattern adherence over time, as it ignores changes in dietary habits and may bias our understanding of the diet-disease pathway.