Bariatric Surgery and Irritable Bowel Syndrome

| February 1, 2019

by Joseph R. Giacolone, BS; Isabella Guajardo, BA; Samuel Torres Landa, MD; Octavia Picket Blakely, MD, MHS; Noel N. Williams, MD; and Kristoffel R. Dumon, MD

Mr. Giacolone and Ms. Guajardo are with Perelman School of Medicine, University of Pennsylvania in Philadelphia, Pennsylvania. Dr. Landa is from Oregon Health & Science in Portland, Oregon. Drs. Picket Blakely, Williams, and Dumon are from the Hospital of the University of Pennsylvania in Philadelphia, Pennsylvania.

Funding: No funding was provided.

Disclosures: The authors report no conflicts of interest relevant to the content of this article.

Bariatric Times. 2019;16(2):12–15.


Abstract

There is significant overlap between those who have obesity and those who have been diagnosed with irritable bowel syndrome as multiple studies have suggested that irritable bowel syndrome is more common in patients with obesity than in the general population. This has led bariatric surgeons, physicians who treat patients with irritable bowel syndrome, and many others to wonder if obesity itself might be an independent contributor to it. In this article, the authors review common symptoms, diagnostic criteria, and subtypes of irritable bowel syndrome. They discuss the relationship between irritable bowel syndrome and obesity, the pathophysiology of both diseases, and research linking surgical and medical weight loss to improved patient outcomes. Although the best available research indicates that there is likely a meaningful relationship between obesity and irritable bowel syndrome, even after correcting for a number of possible confounders, and there appear to be multiple biological differences in patients with obesity that may be predisposing them to manifest irritable bowel syndrome, further research is needed, especially comparative studies evaluating weight loss interventions and their effects on irritable bowel syndrome.

Introduction

The prevalence of obesity in American adults has increased dramatically over the past 20 years. The most recent population data from 2017 shows that a staggering 39.6 percent of Americans aged 20 or older have obesity, an increase of 20.2 percent from 1997.1,2 This considerable rise has coincided with the common observation that this population has a high incidence of functional gastrointestinal (GI) symptoms. As a result, there is significant overlap between those who have obesity and those who have been diagnosed with irritable bowel syndrome (IBS). IBS is a common disease that, according to a recent meta-analysis, affects roughly seven percent of Americans.3 Multiple studies have suggested that IBS is more common in patients with obesity than in the general population, with prevalence rates ranging from 8 to 31 percent.4–8 This association has led bariatric surgeons, physicians who treat patients with IBS, and many others to wonder if obesity itself might be an independent contributor to IBS. A significant amount of work has been done to characterize and clarify this relationship. There are good data which outline a direct connection between the two. Still, the opposing argument that the relationship between obesity and IBS is not as strong is also supported by several studies. The focus of this review is to present the relevant research and discuss its implications, as well as to outline future directions.

Irritable Bowel Syndrome Diagnosis

In order to discuss IBS and its relation to obesity it is beneficial to briefly define IBS, explain its diagnostic criteria, and explain how these factors relate to patients with obesity. Patients often present with vague and nonspecific symptoms, which poses a significant challenge to diagnosing IBS. For this reason, establishing clear diagnostic standards has been a major focus in gastroenterology. The ROME criteria, which are based on symptoms needed to meet the diagnosis of IBS, are now in their fourth iteration since being first introduced in 1992.9 According to ROME criteria, patients must have abdominal pain for at least one day per week for three consecutive months, as well as two of the following three symptoms: pain caused by defecation, change in stool frequency, or change in stool appearance. Patients who meet these criteria still have significant variation in their experience of diarrhea, constipation, or both as the primary complaint. These differences have led to the creation of IBS subtypes, which are defined by the predominant symptom and include IBS-C (constipation predominant), IBS-D (diarrhea predominant), IBS-M (mixed), or unsubtyped.9

Diagnostic certainty about IBS is hence limited by its exclusive reliance on patient-reported symptoms. This problem is compounded in patients with obesity in whom there could be functional GI complaints related to high-volume food intake or other behavioral practices. It is therefore important to be able to distinguish organic IBS from consumption-related symptoms in patients with obesity. Disentangling the confounding impact of high-volume-intake-related symptoms has been the focus of a few studies, which have attempted to accomplish this by studying binge eating disorder in patients with obesity. Levy et al studied a population of patients with obesity in a weight loss program and assessed the association between body mass index (BMI), binge eating status, and the presence of IBS and associated symptoms. While they did find a positive association between binge eating and abdominal pain, bloating, and constipation, they did not observe a statistically significant increase in IBS diagnoses among these patients.10 This suggests that IBS is a disease entity independent of post-prandial or intake-related GI symptoms. A similar study conducted by Italian researchers in 2013 corroborates this assertion. Santonicola et al11 examined the presence of nine different GI symptoms (epigastric pressure, belching, nausea, cough, noncardiac chest pain, dysphagia for liquids, dysphagia for solids, regurgitation, and heartburn) among a group of patients with obesity (n=100) compared to healthy control participants (n=100). Further comparing BE behaviors in the group with obesity, the researchers found that only nausea was significantly higher in those with BE compared to those without, and even this association was borderline (p=.05). These study results support the assumption that the relationship between IBS and obesity can be studied without being significantly confounded by obesity-related eating behaviors. 

Obesity and Irritable Bowel Syndrome

Initial attempts to clarify the relationship between IBS and obesity have looked at IBS prevalence, as well as associated symptoms, in the patient population with obesity. Using the then standard Rome II criteria, Levy et al showed in 2005 that 983 patients with obesity in a weight loss program met IBS diagnostic criteria, corresponding to an incidence of 13.3 percent of patients enrolled in the program.12 Further, a study by Breckan et al13 demonstrates an increased prevalence of IBS in patients with higher BMI when compared to normal weight controls (p<0.0001), and delineates that patients with morbid obesity experience GI symptoms (reflux, dyspepsia, bloating and increased intestinal gas production) with increased severity and intensity when compared to controls.13 A similar study assessed the prevalence of GI symptoms in patients with morbid obesity and control subjects using a previously validated 19-point questionnaire, and found that abdominal pain, gastroesophageal reflux disease (GERD), and reflux were all significantly higher in the patients with morbid obesity. The prevalence of IBS within the studied population was 23 percent.14

More recent studies also support this relationship. A large population-based study of 1,139 patients divided according to BMI and assessed for GI symptoms found that there was a significantly increased prevalence, severity, and intensity of symptoms in patients with higher BMIs compared to their normal weight counterparts.15 A meta-analysis from 2012 focusing on GI symptoms and obesity concluded that upper abdominal pain, GERD, and diarrhea were all significantly associated with obesity, but found no association for lower abdominal pain, bloating, constipation, or nausea. Further, a subgroup analysis of this study revealed that upper abdominal pain was nearly three times as likely to occur among individuals with obesity.16 Similarly, Delgado-Aros et al17 found that patients with BMI more than 30kg/m2 experienced both upper and lower abdominal pain, nausea, and constipation, with increased frequency as compared to controls. Also, functional bowel symptoms in patients with morbid obesity are highly prevalent even after excluding esophageal and intestinal motility disorders.5 Schneck et al further examined the association of GI symptoms and obesity. The findings of this study indicate that there was no difference in age, sex, or BMI between patients with obesity with or without IBS. However, they did find that patients with obesity with IBS reported significantly higher prevalence of GERD and dyspepsia, among other symptoms. Also, patients with obesity with IBS had significantly higher scores of fatigue, anxiety, depression, and poorer quality of life. Those with obesity, IBS, and GERD reported significantly higher IBS severity scores than those without GERD.4 Other studies have also found an association between anxiety and IBS.18,19 

There is also a noteworthy overlap between IBS and other GI disorders. Multiple studies have shown that GERD and IBS frequently overlap in the general population, with higher BMI, anxiety, and somatization as predictors of such overlap.20,21 In addition to the overlap, patients with obesity with IBS reported significantly higher prevalence of GERD and dyspepsia, and had significantly higher scores of fatigue, anxiety, depression, and poorer quality of life.4 Patients with both IBS and GERD reported significantly higher IBS severity scores than those without GERD.

Other studies have focused on IBS in patients awaiting bariatric surgery. A pre-operative cohort of 120 patients with a normal esophagogastroduodenoscopy (EGD) completed a Rome III questionnaire that indicated functional symptoms in 89 percent and IBS in 18 percent of patients, leading the researchers to conclude that functional bowel symptoms are highly prevalent in patients with obesity.5 The association between GI symptoms, IBS, and BMI is also described in the pediatric population, which suggests that these findings may be widely generalizable. A 2014 study found significant association between constipation in children with obesity and overweight compared to normal-weight controls,22 while another study outlined that there was a significantly higher prevalence of obesity in children with IBS than local and statewide control groups.23 There are, however, other studies which contradict these findings. A study from 2010 found that there was no association between IBS and BMI after logistic regression modeling in a cohort of 483 volunteers divided into IBS and non-IBS (control) groups.24 Another study looked at 1,023 patients referred for outpatient endoscopy in the Netherlands who completed a validated bowel symptom questionnaire. They found no demonstrated association between BMI and functional gastrointestinal disorder (FGID) symptoms after logistic regression analysis. The only significant association was between reflux and BMI.25

An interesting study from 2015 attempted to separate general adiposity into meaningful subgroups by investigating the association of visceral adipose tissue (VAT) and IBS.26 Three hundred thirty-six patients were divided into IBS and non-IBS control groups and evaluated for VAT, subcutaneous adipose tissue (SAT), VAT/SAT ratio, and waist circumference. They found that VAT, VAT/SAT, and waist circumference was significantly associated with an increased risk of IBS, especially of the subtype IBS-D. They did, however, specify that BMI itself was not associated with an increased risk of IBS.26 This argues that objective measurements, such as adipose tissue distribution, may be necessary to appropriately describe a relationship between IBS and obesity. The epidemiological data, to summarize, indicates that an association between GI symptoms and BMI has been repeatedly demonstrated, particularly for the specific symptoms of reflux, upper abdominal pain, and diarrhea. There are, however, conflicting reports that make this relationship more precarious, and any quick assumption about their correlation should be carefully considered.

IBS and Bariatric Surgery

These epidemiological associations have led many to wonder if IBS and its associated symptoms can be reversed with bariatric surgery or medical weight loss. It is well known that bariatric surgery leads to greater weight loss and reduction of obesity-associated comorbidities when compared to nonsurgical interventions;27,28 however, it was unclear if these differential benefits extended to patients with obesity suffering from IBS. A study from 2003 analyzed the GI complaints among 36 patients before and six months after laparoscopic Roux-en-Y gastric bypass according to a previously validated 19-point GI symptom questionnaire. Before surgery, abdominal pain, IBS, reflux, and GERD were all significantly worse than controls. After surgery, all of these symptoms had improved significantly and, most convincingly, were at the level of the control group at six months postoperative.29 Researchers went even further in characterizing postoperative symptomatic improvement by following patients with questionnaires every year for five years. A cohort of 763 patients used a 100-point Likert scale to characterize a range of GI symptoms. At one year, 99.5 patients reported significant improvement in these symptoms. This percentage declined to 84.2, 68.4, 57.9, and 47.4 percent, at years 2,3,4, and 5 years, respectively. These data suggest that the symptomatic improvement occurs most significantly in the first year, with progressive decline in subsequent years. The precipitous decrease in the later intervals may be influenced by a selection bias based on patients who chose to continue completing the survey each year.30 A recent study from 2017 included both laparoscopic sleeve gastrectomy (LSG) and RYGB patients before and after surgery. One hundred eighty-six patients were assessed using a GI quality of life index (GIQLI). Total GIQLI score and all sub-scores were significantly improved within 24 months after surgery, and these findings were more robust for those patients who underwent LSG. Possible sex influence on symptoms was analyzed and no difference was found in total GIQLI between male and female patients.31 These studies consistently show that bariatric surgery is effective in reversing functional GI symptoms.

Some have wondered if the impact on functional GI symptoms is unique to surgical intervention, or if this finding can be generalized to other means of achieving weight loss. Evidence has shown that weight loss is significantly associated with improved quality of life and psychological well-being. Recently, Aasbreen et al32 studied GI symptoms in patients with morbid obesity before and after a six-month medical weight management program. Eighty-eight patients, 81 percent of which were women, went from an average BMI of 42 to 38.7kg/m2 during the course of the program. IBS symptoms, evaluated using the IBS-severity scoring symptom demonstrated a statistically significant reduction at the end of the six-month interval, with 19 of 25 measured variables improving significantly.32 This suggests that that the symptomatic improvement from bariatric surgery is related to weight loss and is independent of the characteristics of the surgical intervention.

Pathophysiology of IBS in Obesity

The evidence discussed to this point argues that obesity is associated with both IBS and GI symptoms, and that these symptoms are significantly altered by weight loss and/or bariatric surgery. The reaffirmation of these findings led to further exploration as to what fundamental mechanisms define this process. Pathophysiological explanations of IBS in patients with obesity have proven to be challenging, but some interesting preliminary data have arisen. Studies report that IBS patients have different compositions of their microbiome, leading some to wonder if similar dysbiosis might be found in patients with obesity.33 A recent study evaluated dysbiosis in a cohort of patients separated into the those with morbid obesity with and without IBS, and IBS patients with and without morbid obesity.34 They found that dysbiosis was more prevalent in patients with morbid obesity with and without IBS than healthy controls. The presence of dysbiosis itself was not a significant correlate of an IBS diagnosis. The study, therefore, concluded that dysbiosis is significantly associated with morbid obesity but not with IBS itself.34 Other evidence indicates that different types of dietary fats can modify the gut microbiota in dramatic ways, leading to dysbiosis and inflammation.35 Others have studied intestinal endocrine cell distribution patterns and are evaluating differences that may exist in IBS patients. The density of intestinal endocrine cells in IBS patients is reduced,36 which has led to analysis of specific types, including ghrelin, cholecystokinin, peptide YY, enteroglucagon, and serotonin-secreting cells. Ghrelin is a hormone known to stimulate food intake and subsequent weight gain, and has been shown to be increased in patients with IBS-D, a patient population previously shown to have a significantly increased prevalence of obesity. The other four cell subtypes have all been found to be decreased in patients with IBS, a finding, together with increased ghrelin cell density, that would predict increased appetite and food intake in IBS patients.37

Others have focused on the relationship between BMI, gut motility, and IBS. A prospective trial led by Sadik et al38 used the Rome II criteria and examined the relationships between symptoms in IBS, GI transit as a measure of GI motility, and BMI. They found that high BMI seems to be associated with higher symptom severity for reflux, loose stools, and urgency. These findings were in agreement with recent population-based studies, leading the authors to conclude that IBS patients may be more sensitive to BMI changes and GI transit changes than individuals without obesity. Though much remains unclear, it is likely that the increased prevalence of IBS in the patient population with obesity has a biologic and pathophysiologic explanation. It is possible that eating behaviors in these patients, such as consuming high quantities of certain dietary fats, may alter their normal gut microbiome. This change could subsequently increase their risk of manifesting IBS.

Discussion and Future Directions

The best available research indicates that there is likely a meaningful relationship between obesity and IBS, even after correcting for a number of possible confounders. Statistically significant improvement in IBS and its related symptoms has been shown after bariatric surgery or weight-loss programs, and there appear to be multiple biological differences in patients with obesity that may be predisposing them to manifest IBS.

These results are promising, but there is still much work remaining. A prospective comparison of IBS resolution after bariatric surgery versus medical weight loss programs could evaluate the potential superiority of one intervention. Similarly, these results could be further clarified by comparing LSG to RYGB, which as previously mentioned, may yield different outcomes. This knowledge may help providers caring for patients with IBS patients before and after surgical intervention and/or weight loss programs. Studies examining the best strategies for IBS management in patients with obesity after bariatric surgery or other forms of weight loss may be extremely helpful. It is possible that the best treatments may differ from those used for patients without obesity with IBS. Still, a considerable amount of information is necessary to elucidate the biological differences that underlie IBS pathophysiology in patients with obesity. Discovering the ways in which this may differ from IBS in a normal BMI population might suggest different treatment approaches.

There are a few factors that complicate the study of IBS among patients after bariatric surgery. Bariatric procedures, such as RYGB, alter native anatomy and can modify different normal physiologic functions, such as motility and nutrient absorption. Known conditions associated with RYGB include dumping syndrome, fat malabsorption, and increased risk for bacterial overgrowth and marginal ulcers, among others. It is often difficult to evaluate IBS symptoms in bariatric surgery patients because of these associated confounders. Another point that merits further clarification is establishing whether study participants took medications or supplements, since these are known to contribute to GI upset and may also have an impact on bowel habits (e.g., iron or calcium supplements are associated with constipation). Controlling for medications and over-the-counter supplements in addition to comparing outcomes between surgical or medical weight loss interventions may further inform the improvement of treatment approaches in this population.

Conclusion

This review of the relationship between IBS and obesity outlines epidemiology, bariatric surgery outcomes, and pathophysiology, while suggesting the need for further research to clarify current areas of ambiguity. It is clear that this subject is one of significant importance when considering how incredibly common both obesity and IBS are in American adults. Population models have predicted that 51 percent of American adults will have obesity by 2030.38 This is a profound public health problem that will likely only worsen in the coming years. If these patients are at greater risk for IBS because of their obesity, better understanding the relationship between the two and how best to treat these patients will be critical in the years ahead.

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