Incidence of collagen-induced arthritis is elevated by a high-fat diet without influencing body weight in mice

Obesity is recognised as a risk factor for triggering rheumatoid arthritis (RA), and it can worsen joint deformities1 and diminish the quality of life in patients with RA.2 The reduction of body weight in obese individuals is believed to alleviate RA symptoms.3 Body mass index (BMI) serves as the primary standard for evaluating obesity.4 An increase in BMI by 1 SD notably elevates the incidence rate of RA, suggesting a causal link between higher BMI and an increased risk of developing RA.5 The association between BMI and obesity is straightforward, as a higher BMI typically indicates a greater risk of obesity.4 Obesity is clinically defined as having a BMI of 30 kg/m2 or greater.4 Here, we established collagen-induced arthritis (CIA) models in mice using both regular and high-fat diets (HFDs) to see if HFD can induce severe RA symptoms in mice. CIA mice develop arthritis symptoms, including joint swelling, redness and stiffness, mirroring the clinical features of human RA.6 Therefore, the CIA model has become the prevailing animal model for RA research. Our observations indicated that mice in the HFD sham group exhibited significantly higher body weights compared with regular diet group, in line with previous reports.7 However, the HFD …