Comparison of mediterranean and healthy eating guideline interventions on the dietary inflammatory index in rheumatoid arthritis: results from a dietary randomised controlled intervention trial

Purpose: Anti-inflammatory diets, such as the Mediterranean Diet (MedDiet) have shown positive effects on disease activity in Rheumatoid Arthritis (RA). The Dietary Inflammatory Index (DII) has been associated with RA risk. However, the effect of improving diet quality with a MedDiet and impact on the DII and patient-reported outcome measures (PROMs) has not been investigated. Objectives: To assess the effects of a MedDiet and adherence to the Irish Healthy Eating Guidelines (HEG) on change in DII and to determine whether change in DII and energy-adjusted DII (e-DII) scores is associated with improvements in PROMs in adults with RA in Ireland. Methods: 40 Participants were randomised to a MedDiet (n = 20) or a HEG intervention (n = 20) for 12 weeks. DII was calculated based on food diaries collected. Between and within group data was analysed in SPSS. Results: Baseline e-DII was 0.99 ± 2.37, 0.79 ± 2.60, 1.20 ± 2.16 for total cohort (n = 40), MedDiet, and HEG groups, respectively (p = 0.588). e-DII significantly improved for the cohort following the MedDiet (p = 0.022) and HEG (p = 0.004) groups. Differences in PROMs across tertiles of e-DII change were not statistically significant, irrespective of diet assignment. Participants in the most anti-inflammatory e-DII tertile group had significantly greater intakes of omega-3 fatty acids, dietary fibre, vitamin A, vitamin E, folic acid, and beta-carotene compared to those in the pro-inflammatory tertile group (p < 0.05). Conclusions: Improving dietary quality with either a MedDiet or the Irish HEG improved e-DII scores in a cohort of people living with RA, however, no statistically significant change in PROMs were observed.