Provided is a composition containing isoleucine, leucine and valine as active ingredients for improving or suppressing side effects associated with a steroid treatment and a composition for suppressing muscular atrophy-related gene. The composition improves or suppresses side effects in a steroid treatment such as muscular atrophy, muscular pain, arthritic pain, impaired glucose tolerance, decreased bone metabolism, impaired immunity, loss of appetite, body weight loss, fatigability and the like, and further suppresses muscular atrophy associated with various diseases. In addition, the composition suppresses muscular atrophy associated with promoted expression of muscular atrophy-related gene associated with glucocorticoid excess or renal failure pathology and the like. Therefore, the composition is effective form improving the QOL of patients.