Multi-center trial results published in the American Journal of Gastroenterology suggested that patients with both inflammatory bowel disease (IBD) and obesity do not face an increased risk for hospitalization, IBD-related surgery, or serious infection after starting on new biologic therapies. "Our findings were a bit surprising since prior studies had suggested higher clinical disease activity and risk of flare and lower rates of endoscopic remission in obese patients treated with biologics," stated Dr. Siddharth Singh, MD, MS, director of the IBD Center at the University of California. 

Based on human physiology and body metabolism, it is believed that obesity, largely via visceral adiposity, has a negative impact on IBD owing to the increased production of adipokines, chemokines, and cytokines, such as tumor necrosis factor (TNF) alpha and interleukin-6. Thus, affecting treatment response as well as increasing the risk for complications and infections. In the study, World Health Organization definitions and standards were used to classify the patients into groups having normal BMI, overweight, or obesity. The groups were further analyzed for the risk factors such as all-cause hospitalization, IBD-related surgery, or serious infection. Based on the results, it was found that within 1 year of starting a new biologic therapy, 22.9% of patients required hospitalization, whereas 3.3% required surgery, and 5.8% were hospitalized with a serious infection. 

Cox proportional hazard analyses showed that obesity was not associated with an increased risk for hospitalization vs normal BMI (adjusted hazard ratio [aHR], 0.90), nor was it associated with IBD-related surgery (aHR, 0.62) or serious infection (aHR, 1.11). When analyzed as a continuous variable, BMI was associated with a lower risk for hospitalization but not with IBD-related surgery or serious infection. 

(Source: https://www.medscape.com/viewarticle/976532#vp_2 )