To further investigate if GDF15 deficiency promotes obesity development through regulation of energy substrate utilization or energy expenditure, we put wildtype and GDF15 knockout DIO mice in the Oxymax-CLAMS system and monitored food intake, locomotor activity, O2 consumption and CO2 production for 3 days after acclimation. The gene discussed is GDF15; the disease is obesity due to melanocortin 4 receptor deficiency.