Evidence of Dietary Benefits on RMD Outcomes Is Limited, Review Says

Certain dietary factors may lead to small benefits in 7 rheumatic and musculoskeletal diseases (RMDs); however, existing evidence is extremely limited and not clinically significant, according to a systematic review published in RMD Open.

The RMDs analyzed in this review were osteoarthritis (OA), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), axial spondyloarthritis (axSpA), psoriatic arthritis (PsA), systemic sclerosis (SSc), and gout. The authors noted that of the 24 systematic reviews and 150 original studies included in the final review, most focused on OA and RA.

For each RMD, the authors discussed the effects of animal products, experimental diets, food components, plant-based interventions including fruits and vegetables, minerals and supplements, and vitamins. Multiple RMDs did not have enough evidence to cover all categories.

Evidence for dietary exposures in OA, RA, SSc, and gout was rated as low or very low, and evidence in axSpA was rated very low due to the small number of studies published on the topic.

Evidence specifically for omega-3s in SLE and PsA was rated as moderate but did not demonstrate an effect on outcomes. For other dietary exposures for these 2 RMDs, evidence was rated low or very low.

Overall, no research on any RMDs was deemed high quality.

Although OA and RA had the most evidence among the RMDs, it still was not enough to be significant, according to the review authors.

For OA, diets including fish oil, chondroitin, glucosamine, vitamin D, and avocado soy unsaponifiables—including vitamin E and plant fats—had moderate evidence, but effect sizes were small and not clinically relevant. Similarly, for RA, diets incorporating probiotics, vitamin D, and fish oil or omega-3s had moderate-quality evidence, but either had no effect or an effect size that was likely not clinically significant.

Other studies that investigated outcomes among more than 1 RMD also found little to no significant effect of dietary changes on outcomes.

“One single-arm study of a powdered meal replacement included people with OA and people with RA, reporting a slight improvement in the 50-foot walk test,” the authors added. “A nonrandomized trial assessing linoleic acid included people with RA and people with axSpA and reported no effect on tender or swollen joint count, morning stiffness, grip strength, and ESR [erythrocyte sedimentation rate].”

Beyond the lack of evidence, the authors found that many of the included studies had a moderate or high risk of publication bias, and there was large heterogeneity in the literature, both within and across different RMDs.

The authors concluded that, based on the limited existing evidence, there is no single dietary factor with a meaningful benefit on RMD outcomes.

Because of this, they suggested that future research on the topic should have higher methodological and reporting standards, including long-term follow-up.

“Standardized definitions for different diet exposures should be formulated to allow comparison across studies and standard outcomes assessed,” the authors wrote. “Finally, research into the additive or synergistic effect of different dietary components should be researched, given the complex and interrelated nature of people’s diets.”

Reference

Gwinnutt JM, Wieczorek M, Rodríguez-Carrio J, et al. Effects of diet on the outcomes of rheumatic and musculoskeletal diseases (RMDs): systematic review and meta-analyses informing the 2021 EULAR recommendations for lifestyle improvements in people with RMDs. RMD Open. Published online June 8, 2022. doi:10.1136/rmdopen-2021-002167