Review Article

The Relationship Between Obesity, Bariatric Surgery, and Inflammatory Bowel Disease

Fiorella Cañete; Míriam Mañosa; Ariadna Clos; Eduard Cabré; Eugeni Domènech


Aliment Pharmacol Ther. 2018;48(8):807-816. 

In This Article

Abstract and Introduction


Background: The convoluted relationship between obesity, bariatric surgery and inflammatory bowel disease (IBD) is of increasing interest.

Aim: To analyse evidence regarding the role of bariatric surgery in the development of de novo IBD and its impact on clinical outcomes and safety in patients with established IBD.

Methods: A PubMed/Medline search was performed to identify studies reporting the development of IBD after bariatric surgery and the outcomes of IBD patients after bariatric surgery.

Results: Eighty patients were reported to have developed de novo IBD after bariatric surgery (21% ulcerative colitis [UC], 75% Crohn's disease [CD]), mostly females. Roux-en-Y gastric bypass was the most frequent bariatric technique (80%). Symptoms related to IBD occurred within 1 month and 16 years after surgery. Regarding patients with known IBD undergoing bariatric surgery, 60 patients (35 CD, 24 UC, and 1 unclassified colitis) have been reported. Sleeve gastrectomy was the most frequent bariatric procedure, particularly in CD patients. Acute flares after surgery were observed in only four UC patients. In addition, two retrospective population-based studies described perioperative outcomes of bariatric surgery on IBD patients, demonstrating only a significant increase in small bowel obstruction in these patients.

Conclusions: Bariatric surgery in carefully selected patients with established IBD is technically feasible and probably safe. Development of de novo IBD should be taken into account in individuals with previous bariatric surgery who develop diarrhoea, anaemia or excessive weight loss.


Obesity is a chronic condition leading to deleterious health outcomes, prevalent in both developed and developing countries, affecting children as well as adults, and becoming a worldwide epidemic affecting approximately 650 million people.[1] Obesity is defined by the World Health Organization by means of a body mass index (BMI) ≥30 kg/m2, and this is further classified into three categories: Obesity type I, BMI 30–34.9 kg/m2; obesity type II (severe obesity), BMI 35–39.9 kg/m2; and obesity type III (morbid obesity), BMI >40 kg/m2. According to the World Health Organization, the worldwide prevalence of overweight or obese individuals is approximately 35%.[2]

In parallel with this obesity epidemic, the incidence and prevalence of inflammatory bowel disease (IBD) is rising globally.[3] Despite the trend towards an increasing incidence and prevalence of IBD worldwide (Europe, Asia, Middle East and North America) over recent years,[4] there is a relative paucity of population-level studies reporting the prevalence of obesity among individuals with IBD. Traditionally, IBD was associated with low body weight, and obese IBD patients were considered infrequent. However, the current prevalence of overweight and obesity among IBD patients is similar to that of the general population, at approximately 20%–30%[5] with no differences among CD and UC, and also in adult or paediatric patients.[6,7] Of note, the reported prevalence of severe or morbid obesity among IBD patients is around 2%–5%.[8–10] Furthermore, an increase in body weight, from a minimum mean BMI of 20.8 kg/m2 in 1992, to a maximum mean BMI of 27 kg/m2 in 2001, has been observed among the recruited Crohn's disease (CD) patients included in clinical trials over the past two decades.[11] This rise in the prevalence of obesity in patients with IBD seems to parallel the global obesity epidemic. Furthermore, as the prevalence of obesity increases worldwide, more obese IBD patients are usually seen in routine clinical practice.

Little is known on the influence of obesity on disease itself or the response to therapies. The impact of obesity on IBD phenotype and outcomes has been addressed in some retrospective studies and remains controversial, as stated in a recent review.[5] In relation to its impact on the efficacy of drugs, in spite of some studies addressing the relationship between clinical efficacy and BMI or body weight, scarce data are available using the established definition of obesity. Singh et al[12] recently reported the results of a pooled analysis including all the patients with CD or UC treated with infliximab in the setting of the randomised controlled trials SONIC, ACCENT-I, and ACT 1 and 2. Among 1205 patients, 14% were obese (as defined by a BMI ≥30 kg/m2). No differences in terms of clinical remission or mucosal healing, even when patients were stratified according to the disease type (CD or UC) or the trial design (induction or maintenance), confirming a preliminary observation in a small cohort in clinical practice.[13] No similar data are available for other anti-TNF or anti-integrin drugs. Regarding thiopurines, although BMI has been reported to have a reciprocal effect on efficacy in CD and UC,[14] and lower metabolite levels have been associated with higher BMI,[15] none of these studies assessed these correlation with the accepted criterion of obesity. When looking at surgery, in a retrospective analysis of prospectively collected data among 1494 patients with IBD (of whom 31.5% were obese), obesity was not associated with increased IBD-related surgeries.[16] Similarly, in a retrospective study including 626 IBD patients who underwent laparoscopic colorectal resections (of whom 13% were obese), obesity was an independent predictor of conversion, although it was not associated with a higher morbidity.[17]

Obesity treatment options include lifestyle modification, weight loss pharmacotherapy and a surgical approach. Bariatric surgery is an effective option for weight loss in severely obese individuals. The number of patients undergoing surgery for weight loss has increased dramatically over the last years. Indications for surgery include a BMI >40 or >35 kg/m2 together with at least one severe obesity-related comorbidity (type 2 diabetes, arterial hypertension, sleep apnoea) and the failure of previous conservative attempts to lose weight. Different bariatric surgery techniques have been described, including, the Roux-en-Y gastric bypass, sleeve gastrectomy, duodenal switch and the jejunoileal bypass, with Roux-en-Y gastric bypass as the most commonly performed procedure.[18] The two main mechanisms for weight loss with Roux-en-Y gastric bypass involve a combination of food restriction and bypass of the absorptive and secretory components of the digestive tract.

Late and long-term complications of bariatric surgery may occur, including nutritional deficiencies and gastrointestinal complications like nausea, vomiting, diarrhoea, constipation, abdominal pain and intestinal obstruction. Diarrhoea occurring after bariatric surgery has several potential causes, the most common being dumping syndrome, bile acid malabsorption, small bowel bacterial overgrowth (which may be a consequence of the change in anatomy), food intolerances and a physiological response to the procedure itself as a result of malabsortion.[19,20] These symptoms tend to decline over time with medical treatment and nutritional support. Persistent symptoms or symptoms accompanied by abdominal pain, excessive weight loss, or other alarm signals should raise suspicions of an underlying disease like IBD or a structural complication of surgery. On the other hand, evidence in the literature on the outcome of bariatric surgery among patients with IBD is sparse and mostly from small case series. Recently, two population-based studies evaluating the safety of bariatric surgery in IBD patients and its impact on clinical outcomes have been published.

Despite the increasing interest in the association between obesity, bariatric surgery and IBD, the relationship between them is poorly understood. The aim of this paper was to review evidence regarding the development of IBD after bariatric surgery and the clinical course of patients with IBD undergoing weight loss surgery. We also sought to describe the potential role of bariatric surgery in the pathogenesis of de novo IBD, its incidence and its impact on clinical outcomes and safety in patients with established IBD.