The nutritional impact of inflammatory bowel disease is notable, both in Crohn's disease and ulcerative colitis. The causes of malnutrition include decreased intake, maldigestion, malabsorption, accelerated nutrient losses, increased requirements, and drug-nutrient interactions. Inflammatory bowel disease causes alterations in body composition and, because of these changes, affects energy expenditure. Various approaches have been most effective in correcting malnutrition, supporting growth, and managing short-bowel syndrome, but the success of primary therapy has been limited.