What predicts obesity in patients with rheumatoid arthritis? An investigation of the interactions between lifestyle and inflammation.

Objective: To assess whether physical activity, diet or inflammation is a more important determinant of body mass index (BMI) and body fat (BF) in patients with rheumatoid arthritis (RA).

Methods: A total of 150 RA patients (102 female) were assessed for BMI and BF. Their habitual physical activity was assessed with the international physical activity questionnaire (IPAQ) and their energy intake with a 3-day food diary. Pro-inflammatory cytokines (interleukins, IL-1 and IL-6, and tumor necrosis factor-alpha), erythrocyte sedimentation rate, C-reactive protein, disease activity score-28 and physical function (Health Assessment Questionnaire-HAQ) were also measured.

Results: BMI correlated inversely with IPAQ (r=-0.511, P=0.000) and positively with energy intake (r=0.331, P=0.016) and HAQ (r=0.133, P=0.042). BF correlated inversely with IPAQ (r=-0.575, P=0.000) and positively with HAQ (r=0.201, P=0.037). Normal weight patients were more physically active compared with those who were either overweight (P=0.006) or obese (P=0.000). Underweight patients consumed significantly fewer calories compared with other patients (P<0.05 in all cases). Cytokines or HAQ did not differ between weight groups. IPAQ was the sole predictor of obesity, whereas energy intake was the sole predictor of underweight.

Conclusions: Inflammation does not seem to influence BMI and BF in RA. As in the general population, high levels of habitual physical activity associate with low BMI and BF in RA. Energy intake is a major determinant of being underweight in those who consume fewer calories. Further research is needed to investigate the suitability of exercise and diet modalities, and their effects on the body composition of RA patients.