Association between a gut microbiota-targeted dietary index and osteoarthritis/rheumatoid arthritis: a cross-sectional study

BACKGROUND: Diet plays a key role in regulating the gut microbiota. This study aimed to investigate the association between the Dietary Index of the Gut Microbiome (DI-GM) ‒ a score designed to reflect the potential of a diet to support a healthy gut microbiota ‒ and different types of arthritis, an area where systematic studies remain scarce. METHODS: Data from the National Health and Nutrition Examination Survey (NHANES) 2007-2018 were analyzed using multivariable logistic regression, Restricted Cubic Spline (RCS) regression, and subgroup analyses to assess associations between DI-GM and Osteoarthritis (OA) and Rheumatoid Arthritis (RA). RESULTS: A total of 6168 participants were included, among whom 506 had Osteoarthritis (OA) and 303 had Rheumatoid Arthritis (RA). Multivariable analyses showed no significant association between DI-GM and OA (p > 0.05), but significant inverse associations with RA across models (ORs 0.74, 0.64, and 0.74; all p < 0.05). Restricted cubic spline analysis detected no significant nonlinear relationships for either outcome. Subgroup analyses suggested potential associations within certain populations. CONCLUSION: This cross-sectional study found an inverse association between the diet-based DI-GM score and RA, but no significant association with OA. Given the limitations of the cross-sectional design, the observed association is equally compatible with dietary changes resulting from RA diagnosis and management (reverse causality). As this study did not measure the gut microbiota, the role of the microbiome as a mediator remains speculative. Therefore, these results require confirmation in prospective studies that can account for reverse causation and directly assess the gut microbiome.