Relative muscle mass is preserved during weight loss in rheumatoid arthritis: a post-hoc RCT analysis

Why clinicians should know about it

• Picked for Endocrinology, Diabetes and Metabolism (paper of the day, 20 July 2026).
• Picked for Rheumatology (paper of the day, 20 July 2026): Post‑hoc RCT analysis of muscle mass preservation during weight loss

Abstract

OBJECTIVES: Obesity and sarcopenia commonly coexist in RA, compounding metabolic risk and disability. Intentional weight loss may improve outcomes but raises concern for accelerated muscle loss. We conducted a post-hoc analysis of a randomized controlled trial (RCT) of a hypocaloric, high-protein diet in adults with RA and obesity to determine whether diet-induced weight loss was associated with disproportionate reductions in muscle mass. METHODS: Adults with RA and obesity were randomized to a 12-week hypocaloric, high-protein diet or to control dietary advice (NCT02881307). DXA was performed at baseline and 12 weeks. Fat mass index (FMI), appendicular lean mass index (ALMI) and adiposity-adjusted ALMI (ALMIFMI) were derived and standardized to Z-scores using national reference data. Between-group differences in change were compared using t-tests, with FDR-adjusted P values reported for all analyses. RESULTS: Participants in the dietary intervention achieved significant reductions in total fat mass (mean change in FMI Z-score -0.35 vs 0.04; P = 0.003). Changes in ALMI Z-score (-0.37 vs -0.43; P = 0.92) and ALMIFMI Z-score (-0.15 vs -0.55; P = 0.92) did not differ significantly between groups. In the intervention group there was minimal decline in ALMFMI, suggesting parallel reductions in lean and fat tissue. CONCLUSION: In adults with RA and obesity, diet-induced weight loss reduced adiposity without evidence of disproportionate muscle loss. These findings support the safety of structured, protein-adequate weight-loss interventions in this population.

Abstract as published, via PubMed.