This case study examined changes in body composition, resting metabolic rate (RMR), aerobic capacity, and daily physical activity in a patient who had ulcerative colitis who underwent ileal pouch‒anal anastomosis (IPAA) surgery. Body composition, RMR, and VO2 peak were assessed prior to, 4, 8, and 16 weeks after IPAA surgery. Daily physical activity data was extracted from a wrist-worn activity tracker preoperatively and 16 months postoperatively. At baseline, total body mass was 95.3 kg; body fat, 11.6 %; lean body mass, 81.1 kg; RMR, 2,416 kcal/d; and V̇O2peak, 42.7 mL/kg/min. All values decreased from baseline at 4 weeks postoperatively, body mass was 85.2 kg (-10.5%); body fat, 10.9% (-6.0%); lean body mass, 73.1 kg (-9.9%); RMR 2,210 kcal/d (-8.5%) and V̇O2peak, 25.5 mL/kg/min (-40.3%). At 16 weeks postoperatively, most parameters were near their baseline levels (within 1%-7%); exceptions were V̇O2peak, which was 20.4% below baseline, and RMR, which increased to nearly 20% above baseline. After the patient had an IPAA surgery, his total and lean body masses, RMR, and aerobic capacity were markedly decreased. Daily physical activity decreased postoperatively and likely contributed to the decreased aerobic capacity, which may take longer to recover compared to body composition and RMR parameters.