Lean body mass (LBM) deficits in youth with Inflammatory Bowel Disease (IBD) are well-established and persist despite achievement of remission and restoration of body mass. LBM deficits are associated with both short and long-term health outcomes including sarcopenia, metabolic dysregulation, and development of osteopenia/osteoporosis. LBM deficits are multifactorial though largely explained by inflammatory processes, inadequate dietary intake, and increased energy needs. Physical activity (PA) may also play a role in LBM deficits.