OBJECTIVES:Several investigators have reported that clinical improvements of patients with rheumatoid arthritis (RA), from participating in therapeutic diet intervention studies, have been accompanied by loss of body weight. This has raised the question whether weight reduction per se can improve RA. In order to test this hypothesis, three previously conducted diet intervention studies, comprising 95 patients with RA, were pooled. Together with Age, Gender, and Disease Duration, change during the test period in body weight, characterised dichotomously as reduction or no reduction (dichoDeltaBody Weight), as well as Diet (dichotomously as ordinary diet or test diet), were the independent variables. Dependent variables were the difference (Delta) from baseline to conclusion of the study in five different disease outcome measures. DeltaESR and DeltaPain Score were both characterised numerically and dichotomously (improvement or no improvement). DeltaAcute Phase Response, DeltaPhysical Function, and DeltaTender Joint Count were characterised dichotomously only. Multiple logistic regression was used to analyse associations between the independent and the disease outcome variables. RESULTS:Statistically significant correlations were found between Diet and three disease outcome variables i.e. DeltaAcute-Phase Response, DeltaPain Score, and DeltaPhysical Function. Delta Body Weight was univariately only correlated to DeltaAcute-Phase Response but not significant when diet was taken into account. CONCLUSION:Body weight reduction did not significantly contribute to the improvement in rheumatoid arthritis when eating lacto-vegetarian, vegan or Mediterranean diets.