Various lifestyle factors including physical activity and obesity, stress, sleep, and smoking may modify the risk of developing inflammatory bowel diseases (IBDs). In patients with established IBD, these lifestyle factors may significantly impact the natural history and clinical outcomes. Recreational exercise decreases the risk of flare and fatigue in patients with IBD. In contrast, obesity increases the risk of relapse and is associated with higher anxiety, depression, fatigue, and pain and higher health care utilization. Obesity also modifies pharmacokinetics of biologic agents unfavorably and is associated with a higher risk of treatment failure. Sleep disturbance is highly prevalent in patients with IBD, independent of disease activity, and increases the risk of relapse and chronic fatigue. Similarly, stress, particularly perceived stress rather than major life events, may trigger symptomatic flare in patients with IBD, although its impact on inflammation is unclear. Cigarette smoking is associated with unfavorable outcomes including the risk of corticosteroid dependence, surgery, and disease progression in patients with Crohn's disease; in contrast, smoking does not significantly impact outcomes in patients with ulcerative colitis, although some studies suggest that it may be associated with a lower risk of flare. The effect of alcohol and cannabis use in patients with IBD is inconsistent, with some studies suggesting that cannabis may decrease chronic pain in patients with IBD, without a significant effect of biological remission. Although these lifestyle factors are potentially modifiable, only a few interventional studies have been conducted. Trials of structured exercise and psychological therapy including mindfulness-based therapies such as meditation and yoga and gut-directed hypnotherapy have not consistently demonstrated benefit in clinical and/or endoscopic disease activity in IBD, although may improve overall quality of life.