Mediterranean diet and health outcomes in idiopathic inflammatory myopathies

The clinical relevance of Mediterranean diet (MedDiet) and determinants shaping adherence across disease phenotypes remain largely unexplored in idiopathic inflammatory myopathies (IIM). In this study, we evaluated MedDiet adherence across IIM subtypes, identified factors associated with it, and examined its association with patient-reported health outcomes.

Adults with self-reported specialist-diagnosed IIM participating in the international Collating the Voice of People with Autoimmune Diseases survey were included. Mediterranean diet adherence was assessed using the 14-item Mediterranean Diet Adherence Screener (MEDAS). Linear regression models were used to identify demographic, disease-related and socioeconomic predictors of MEDAS adherence. Additional multivariable models evaluated associations between MEDAS scores and patient-reported outcomes after adjustment for demographic, socioeconomic, disease-related and treatment-related covariates. Phenotypes were explored using factorial analysis with hierarchical clustering.

Among 859 participants with IIM, MedDiet adherence was generally modest and varied across disease subtypes, with the lowest adherence observed in inclusion body myositis. Female sex, autoimmune multimorbidity and fewer household members were independently associated with higher MEDAS scores. In adjusted outcome models, higher MEDAS adherence was independently associated with better physical function (PROMIS PF-4), better global physical health (PROMIS GPH), lower disease activity, lower fatigue and lower pain. These associations remained significant after adjustment for disease activity, glucocorticoid exposure, immunosuppressant use, food security and income adequacy.

Higher MedDiet adherence was associated with more favourable patient-reported physical health, function and symptom burden among individuals with IIM. However, because of the cross-sectional design, the direction and causality of these relationships cannot be determined. Prospective studies are needed to establish whether improving dietary adherence can influence clinical outcomes in IIM.