Evolution of Total Energy Expenditure and Its Various Components in Active Rheumatoid Arthritis (RA)Treated With Anti-TNF Agents and Comparison With Healthy Subjects

Few studies have been focused on the combined evolution of body composition, energy expenditure, physical activity, muscle performance, and nutritional intake in patients taking anti-TNFs.

This study's objective is to assess the impact of anti-TNF treatment during the first year of administration on the energy metabolism of RA patients, measuring variations in basal daily energy expenditure and per type of expenditure using indirect calorimetry with calorimetric chambers. Investigator also aim to define standardized values for RA patients compared to healthy matched controls and to be able to monitor the evolution of these different values during treatment compared to this standard.

This will be an exploratory study with a longitudinal follow-up of the cohort in patients treated in a market authorization context and involving a case/control study. Investigator judged the inclusion of healthy controls justified by the current lack of data comparing the different components of energy metabolism in active RA patients versus healthy subjects using calorimetric chamber measurement. The aim is to obtain reference values to situate RA-specific values in comparison before and after treatment. Investigator considered selecting controls from the RA patients unjustified given how essential it is to commence treatment in active RA cases (1 year with placebo not justifiable). A previously-treated inactive RA population with no inflammation would not be comparable to patients with active RA, and neither would a population with active RA treated with conventional treatment or a different biotherapy to anti-TNFs. Investigator also chose to perform a second assessment at 6 months without calorimetric chamber measurement but rather an indirect measurement using actimetry in order to limit costs and patients lost-to-follow-up due to treatment modification (failure or intolerance), all the while maintaining full assessment at 12 months. Scheduling the assessment at 12 months is justified by published studies' reports of delay before significant weight gain manifests, and enables us to maintain homogeneity as regards variations in physical activity and nutritional intake linked to seasonal changes.