To investigate the effects of a dietary intervention on arthritis pain and disease severity, 44 adults previously diagnosed with rheumatoid arthritis were randomly assigned to a Diet phase (vegan diet for 4 weeks, elimination of additional foods for 3 weeks, and then reintroduction of the eliminated foods individually over 9 weeks) or a Supplement (placebo) phase for 16 weeks. After a 4-week washout, they then switched to the opposite phase. The Disease Activity Score-28 (DAS28) decreased from 4.5 to 2.5 (P <
.001) in the Diet phase and from 3.2 to 2.9 (P = .41) in the Supplement phase (between-group P = .01). The mean number of swollen joints decreased from 7.0 to 3.3 in the Diet phase (P = .03) and increased from 4.7 to 5 in the Supplement phase (P = .63
between-group P = .047). In a subanalysis excluding individuals who increased medications during the study, DAS28 decreased 1.9 points in the Diet phase (P = .003) and .4 points in the Supplement phase (P = .27
between-group P = .04). In a further subanalysis limited to participants making no medication changes, DAS28 decreased 1.5 points in the Diet phase (P = .009) and .3 points in the Supplement phase (P = .40, between-group P = .11). We conclude that the dietary intervention was associated with symptomatic improvements. TRIAL REGISTRATION: Clinicaltrials.gov NCT01544101, NCT01700881, NCT03417648, and NCT03580681.