Introduction: Gluten-free diet (GFD), the mainstay of gluten-associated disorder (GAD) treatment, relies on patient adherence to optimize its therapeutic value. Psychological distress and decreased quality of life are associated with GFD non-adherence, but longitudinal assessments of psychosocial health’s impact on dietary adherence are lacking. Our study is the first to explore mental health status and motivational factors (eg, motivation type, perceived competence), and their connection with longitudinal changes in GFD adherence. Methods: In our prospective study, we invited patients with self-reported GAD from the UCLA Celiac Collective to complete baseline (2016-2020) and follow-up (2022) surveys. Surveys captured demographics, medical history, and responses to the Celiac Dietary Adherence Test; Celiac Symptom Index; PRO Measurement Information System’s depression, anxiety, sleep disturbance, fatigue, pain, and social satisfaction domains; Celiac Disease Quality of Life; Treatment Self-Regulation Questionnaire for motivation; Perceived Competence Scale; and Health Care Climate Questionnaire for relationship with healthcare provider. Cross-sectional analyses of GFD adherence, the primary outcome, used McNemar’s and Wilcoxon rank-sum tests; the longitudinal analysis assessed changes in GFD adherence from baseline to follow-up with T-tests. Results: We identified 449 patients with GAD at baseline (87.9% female, mean age 48). Of those patients, 123 completed follow-up. Factors consistently associated with higher GFD adherence at baseline and follow-up were lower scores for disease activity, anxiety, depression, fatigue, pain; and higher competence, autonomous motivation, and social satisfaction. Forty-4 patients whose GFD adherence declined over time also saw an increase in disease activity, depression, fatigue; and a decrease in social satisfaction. Conclusion: This is the first longitudinal study to show that intrinsic (or autonomously) motivated GAD patients who perceived themselves to be competent in complying with a GFD achieved better adherence, which in turn was linked to less distress and disease activity. This pattern emerged at both assessment periods and suggests that specific motivational behaviors may drive GFD adherence and its therapeutic value. Providers, whose influence is demonstrated by the positive association seen between patient-provider relationships and adherence, should treat GAD by considering these intrinsic behavioral qualities while addressing mental health disorders. Table 1. - Measures associated with GFD adherence Non-Adherence (CDAT ≥ 13) Adherence (CDAT < 13) P-value Worsened Adherence Improved Adherence P-value Celiac Disease Activity (CSI) Baseline 45.0 (37.0-51.0) 29.0 (23.0-36.0) < 0.001 +4.2 (8.3) -2.8 (8.2) 0.002 Follow-up 38.5 (36.0-45.5) 32.0 (25.5-36.5) < 0.001 Anxiety (PROMIS-29) Baseline 9.0 (6.0-12.0) 6.0 (4.0-8.0) < 0.001 +1.2 (2.7) 0.0 (3.9) 0.154 Follow-up 9.0 (6.0-11.0) 7.0 (4.0-9.8) 0.018 Depression (PROMIS-29) Baseline 7.0 (4.2-10.0) 4.0 (4.0-6.0) < 0.001 +1.1 (2.1) -0.6 (3.3) 0.014 Follow-up 7.0 (5.0-9.0) 4.0 (4.0-5.0) < 0.001 Sleep (PROMIS-29) Baseline 10.0 (8.0-12.0) 7.0 (5.0-9.0) < 0.001 +0.4 (2.6) +0.3 (3.3) 0.842 Follow-up 9.0 (7.0-11.0) 8.0 (6.0-10.0) 0.185 Fatigue (PROMIS-29) Baseline 13.0 (9.5-16.0) 8.0 (6.0-10.0) < 0.001 +1.5 (2.8) -1.1 (3.2) < 0.001 Follow-up 12.0 (10.0-15.0) 8.0 (6.5-10.5) < 0.001 Satisfaction with Social Interaction (PROMIS-29) Baseline 10.0 (7.0-12.0) 14.0 (12.0-16.0) < 0.001 -1.0 (3.5) +1.0 (3.2) 0.019 Follow-up 10.0 (8.0-12.0) 15.0 (12.0-16.0) < 0.001 Pain (PROMIS-29) Baseline 9.0 (5.5-14.0) 4.0 (4.0-8.0) < 0.001 +0.6 (4.0) -0.8 (4.0) 0.15 Follow-up 8.0 (6.8-12.0) 5.0 (4.0-7.2) < 0.001 Relationship with Healthcare Provider (HCCQ) Baseline 21.0 (12.0-33.5) 25.0 (15.0-36.0) 0.05 -0.4 (11.2) +4.7 (8.6) 0.051 Follow-up 23.5 (14.2-29.8) 27.5 (19.5-38.2) 0.044 Competence (PCQ) Baseline 26.0 (22.8-28.0) 28.0 (27.0-28.0) < 0.001 +0.2 (2.2) +1.7 (4.2) 0.068 Follow-up 28.0 (25.0-28.0) 28.0 (28.0-28.0) 0.002 Autonomous Motivation (TSRQ) Baseline 40.0 (36.0-42.0) 42.0 (38.5-42.0) < 0.001 -1.1 (6.4) +1.1 (6.8) 0.172 Follow-up 40.0 (35.0-42.0) 42.0 (41.8-42.0) 0.003 Controlled Motivation (TSRQ) Baseline 16.5 (8.2-23.0) 13.0 (7.2-23.0) 0.444 -3.2 (7.9) -0.8 (6.4) 0.187 Follow-up 12.5 (6.0-22.0) 12.0 (6.8-20.0) 0.912 Amotivation (TSRQ) Baseline 4.0 (3.0-8.0) 4.5 (3.0-9.0) 0.988 -0.4 (3.9) -0.1 (4.4) 0.759 Follow-up 5.0 (3.0-8.0) 4.0 (3.0-7.8) 0.628 Quality of Life (CDQoL) Baseline 62.0 (49.0-77.0) 50.0 (37.0-59.5) < 0.001 -1.1 (12.6) -2.5 (12.4) 0.786 Follow-up 50.0 (43.2-63.5) 45.5 (40.0-52.5) 0.252 Data on the right ("Worsened Adherence" & "Improved Adherence") represent change of score means (SD) from baseline to follow-up. CDAT: Celiac Dietary Adherence Test; CSI: Celiac Symptom Index; PROMIS: PRO Measurement Information System; CD-QOL: Celiac Disease Quality of Life; TSRQ: Treatment Self-Regulation Questionnaire; PCS: Perceived Competence Scale; HCCQ: Health Care Climate QuestionnaireData from the left half of the Table (under "Non-Adherence" & "Adherence") represent score medians (Q1-Q3) at baseline and follow-up.