Smoking, physical activity, nutrition and lifestyle: environmental factors and their impact on IBD.

Current smoking increases the risk of developing Crohn's disease and worsens its course, increasing the need for steroids, immunosuppressants, and re-operations. On the contrary, smoking protects against ulcerative colitis and after disease onset improves its course, decreasing the need for colectomy. Smoking cessation improves Crohn's disease and worsens ulcerative colitis. Achieving smoking cessation in Crohn's disease is thus an important goal of therapy, whereas patients with ulcerative colitis should not be discouraged to quit, because the beneficial effect of smoking for their disease is counterbalanced by the deleterious respiratory and cardiovascular effects of tobacco. Physical activity improves quality of life without detrimental effect on disease activity, and may contribute to increase muscle mass and to prevent osteoporosis. Regarding nutrition, a Western diet may be associated with an increased risk of IBD, and a case-control study revealed an increased consumption of linoleic acid before diagnosis of ulcerative colitis. Liquid diets may improve Crohn's disease flares and decrease the need for steroids; however, there are no defined diets able to improve the disease course, and in Crohn's disease, supplementation with omega-3 fatty acids did not show a significant benefit. Obesity is becoming more prevalent in IBD and may be associated with higher disease activity. In total, adhering to four simple lifestyle factors - never smoking, physical activity, prudent diet and body mass index <25 - may have a strong impact both on the prevention of major chronic diseases and on the course of IBD.