Heart Rate Variability (HRV), the variation in time between each heartbeat, is a proxy for vagus nerve function and validated indicator of cardiovascular health. Lower HRV is associated with increased risk of cardiac events and greater vulnerability to psychological stress. Fatigue is a common, frustrating and persistent symptom for IBD patients, with multifaceted mechanisms including nutrient deficiencies, inflammation, and poor sleep. Lower HRV is associated with higher fatigue in patients with cancer and myalgic encephalomyelitis.