Fructose malabsorption associated with functional abdominal bloating: Case-control study

Abstract

BACKGROUND

Abdominal bloating is a common symptom in patients with functional gastrointestinal disorders (FGIDs). The pathophysiology of bloating remains poorly understood. Fructose malabsorption (FM) has been implicated in the pathogenesis of various FGIDs. However, there is limited data on the role of FM in patients with functional abdominal bloating.

AIM

To investigate the prevalence and predictors of FM in patients with functional bloating.

METHODS

This case-control study included 70 patients with functional bloating who met the Rome III criteria and 35 healthy controls. All participants were initially tested for small intestinal bacterial overgrowth, and those who tested negative subsequently underwent a fructose hydrogen breath test (FHBT) to evaluate FM. Breath hydrogen and methane levels were measured at baseline and every 15 minutes for 3 hours. A rise in breath hydrogen or methane levels > 20 ppm above baseline was considered positive. Symptoms were recorded during the test.

RESULTS

FM was detected in 20/70 (29%) patients with functional bloating, compared with 1/35 (3%) in healthy controls (P = 0.01). 51/105 (48%) participants had symptoms during the test, and subjects with positive FHBT had a significantly higher prevalence of symptoms than those with negative FHBT (76% vs 42%; P < 0.01). A subset of patients with functional bloating who tested negative for FHBT had symptoms during FHBT, suggesting a mechanism beyond FM, such as visceral hypersensitivity, in the pathogenesis of functional bloating (80% vs 62%; P = 0.14). Female sex was an independent predictor of FM in the multivariate analysis (P = 0.02). Methane producers were present in 32/70 (46%) patients.

CONCLUSION

More than one-fourth of patients with functional bloating had FM. Future multicentre prospective studies should evaluate the role of fructose-restricted diets in managing functional bloating.

Key Words: Fructose malabsorption; Fructose intolerance; Functional bloating; Small intestinal bacterial overgrowth; Methane producer

Core Tip: Fructose malabsorption (FM) is increasingly recognised as a contributor to functional gastrointestinal symptoms. In this case-control study, FM was significantly more common in patients with functional abdominal bloating than in healthy controls (29% vs 3%). A subset of patients with functional bloating who tested negative for the fructose hydrogen breath test (FHBT) had symptoms during the FHBT, suggesting a mechanism beyond fructose malabsorption, such as visceral hypersensitivity, in the pathogenesis of functional bloating. Female sex was identified as an independent predictor. These findings suggest that FM may be an important, potentially modifiable factor in patients presenting with functional bloating.

INTRODUCTION

Abdominal bloating is one of the most common complaints in gastroenterology outpatient clinics. It affects 96% of patients with functional gastrointestinal disorders (FGIDs), and population studies estimate the prevalence of bloating to range between 16% and 30% in the general population[1,2]. Given its high prevalence, bloating significantly affects the quality of life, with affected individuals reporting a significant reduction in daily activities[1,3].

Bloating is most commonly associated with FGIDs, such as functional dyspepsia (FD), irritable bowel syndrome (IBS), celiac disease, and functional constipation[4]. When bloating is not part of another FGID, it is classified as an independent entity in the Rome IV criteria as functional abdominal bloating/distension (FABD). It is defined as recurrent bloating and/or visible distension occurring, on average, at least once a week, with symptom onset at least six months before diagnosis[5]. The pathophysiology is poorly understood, and theories regarding the cause of bloating range from gas accumulation and improper gas handling to impaired bowel propulsion and psychological factors, with no single mechanism adequately explaining all cases[6]. Several studies have demonstrated that sugar malabsorption or intolerance to sugars, including lactose, fructose, and sorbitol, is associated with symptoms such as bloating and flatulence in FGIDs, including IBS[7].

Fructose is naturally present and widely used as a sweetener in food. Fructose intolerance or malabsorption has been reported to range from 2.4% to 5.7% among healthy controls in various studies and from approximately 40% to 45% in patients with various FGIDs[8-12]. The role of fructose intolerance or malabsorption has been studied in FGIDs, especially IBS. However, the role of fructose malabsorption (FM) in patients with isolated functional abdominal bloating remains poorly understood. In this case-control study, we aimed to determine the frequency of FM and its clinical predictors in patients with functional abdominal bloating, compared with healthy controls, using the FHBT.

MATERIALS AND METHODS

This case-control study was conducted at the Department of Gastroenterology, Govind Ballabh Pant Institute of Post Graduate Medical Education and Research, New Delhi, from January 2015 to September 2016. The Institutional Ethics Committee of MAMC (F. No. 11/IEC/MAMC/2011/206) approved the study. Consecutive patients with functional bloating who attended the outpatient department and age- and sex-matched healthy controls were included in the study.

Inclusion and exclusion criteria

Patients aged 18-75 years who met the Rome III criteria for functional bloating were included. Age-and sex-matched healthy individuals without gastrointestinal or other disorders were recruited as controls. Participants were excluded if they had known or suspected hereditary fructose intolerance, abdominal pain, altered bowel habits (diarrhea or constipation), diabetes mellitus, hypothyroidism, hyperthyroidism, or connective tissue disorders. Individuals with a history of gastrointestinal surgery, alcohol or other substance abuse, severe systemic diseases, including cardiac, hepatic, renal, or respiratory failure, pregnancy or lactation, organic or other functional gastrointestinal diseases, human immunodeficiency virus infection, other immunodeficiency disorders, or malignancy were also excluded. Participants who received antibiotics, probiotics, pro- or anti-motility drugs, or bowel preparation for colonoscopy within four weeks prior to the study were excluded. Patients with alarm features, such as unintended significant weight loss, gastrointestinal bleeding, prolonged fever, or a family history of inflammatory bowel disease or colorectal cancer, were excluded. Participants who tested positive for small intestinal bacterial overgrowth on the glucose hydrogen breath test (GHBT) were also excluded.

Diagnosis of functional bloating and workup

The Rome III criteria were used to diagnose functional bloating, requiring both the following: (1) A recurrent feeling of bloating or visible distension at least three days per month in the last three months; and (2) Insufficient criteria for a diagnosis of FD, IBS, or other functional gastrointestinal (GI) disorders, with criteria fulfilled for the last three months and symptom onset at least six months before diagnosis[13]. All patients underwent the following baseline investigations: Complete hemogram, renal function tests, serum electrolytes, liver function tests, tissue transglutaminase immunoglobulin A (IgA), and routine microscopic examination of stool.

Breath hydrogen and methane levels were measured using an SC Microlyser (Quintron, United States). Both the case and control groups were initially evaluated for small intestinal bacterial overgrowth (SIBO) using the GHBT. Participants who tested positive for GHBT were excluded from the study. The remaining cases and control subjects underwent FHBT to evaluate FM.

Evaluation for SIBO

All patients and controls underwent GHBT after an overnight fast. Breath hydrogen and methane concentrations were measured at baseline, and the average of four values was used as the basal hydrogen/methane level. The participants then ingested 100 g of glucose dissolved in 200 mL of water, and breath hydrogen and methane values were measured every 15 minutes for 3 hours. A sustained rise in breath hydrogen or methane > 12 ppm above the baseline level for at least two readings was considered diagnostic of SIBO[14]. Participants with fasting methane concentrations ≥ 3 ppm were considered methane producers[15-17].

Evaluation of FM

FM was assessed using the FHBT following an overnight fast, and the patients were advised to avoid fructose-rich foods for 48 hours before the test. Breath hydrogen and methane concentrations were measured at baseline, and the average of four values was used as the basal hydrogen/methane levels. The participants then ingested 25 g of fructose dissolved in 250 mL of water, and breath hydrogen and methane values were measured every 15 minutes for the next 3 hours. A persistent rise in breath hydrogen or methane > 20 parts per million above the basal level for at least two readings was considered diagnostic of FM[12].

Statistical analysis

The sample size was calculated using the Epi-Info software (version 7.15; Centers for Disease Control and Prevention, Atlanta, GA, United States). The patient-to-control ratio was 2:1, and the study power was 80% with a 2-sided 95% confidence interval. No studies have specifically evaluated FM in functional bloating. Therefore, we calculated the sample size based on previous studies on FM in IBS. The average frequency of FM with 25 g of fructose among patients with functional bloating and healthy controls was estimated at 30% and 5%, respectively, yielding sample sizes of 68 and 34 for patients and controls[12,18]. We included 70 patients with functional bloating who met the Rome III criteria and 35 healthy controls in our study. Informed consent was obtained from all patients after explaining the nature and possible consequences of the study prior to their enrollment.

Data were analyzed using SPSS software (version 15.0). Categorical and continuous data are expressed as proportions, medians, and ranges, respectively. Categorical and continuous data were analyzed using the χ² and Mann-Whitney U tests, respectively. Statistical significance was set at P < 0.05. Univariate analysis, followed by multivariate logistic regression, was performed to identify independent clinical predictors of FM among patients with functional bloating.

RESULTS

During the study period, 71 patients who satisfied the Rome III criteria for functional bloating and 35 healthy controls were enrolled. One patient was positive for SIBO on GHBT and was subsequently excluded. None of the control subjects had positive GHBT results. A total of 105 participants, including 70 patients with functional bloating and 35 healthy controls, were included in the study and underwent FHBT (Figure 1). The age, sex, and body mass index (BMI) of the cases and controls were comparable across all parameters (Table 1). The dietary patterns of the patient and control groups were comparable (P = 0.52; Table 1). All patients had normal hemograms, and no abnormalities were detected on routine stool microscopy. None of the patients had a positive IgA-tTG result, excluding celiac disease as a contributing diagnosis.

Figure 1 Study protocol. FM: Fructose malabsorption; GHBT: Glucose hydrogen breath test; FHBT: Fructose hydrogen breath test.

Table 1 Baseline characteristics of cases and controls, n (%).

Characteristics	Cases (n = 70)	Controls (n = 35)	P value
Age (years), median (range)	32.5 (18-74)	32 (18-48)	0.81
Gender	Males: 36 (51)	Males: 19 (54)	0.78
BMI (kg/m2), median (range)	22.3 (12.5-31.2)	21.9 (17.9-31.6)	0.82
Dietary pattern	Mixed: 52 (74)	Mixed: 28 (80)	0.52

BMI: Body mass index.

FHBT outcomes

FM was significantly higher in cases compared to healthy controls [1/35 (3%) vs 20/70 (29 %); P = 0.01] (Figure 2). Overall, 51 of the 105 participants (49%) experienced gastrointestinal symptoms during the FHBT. A significantly higher proportion of patients with functional bloating (43/70; 67.14%) reported symptoms during testing than the controls (4/35; 11.4%) (P < 0.01). Patients with positive FHBT had a significantly higher prevalence of symptoms during the test than those with negative FHBT (76% vs 42%; P < 0.01) (Figure 3).

Figure 2 Comparison of fructose hydrogen breath test between cases and controls. FHBT: Fructose hydrogen breath test; OR: Odds ratio; CI: Confidence interval.

Figure 3 Comparison of symptoms generation between cases and controls, and fructose hydrogen breath test positive and fructose hydrogen breath test negative study subjects. FHBT: Fructose hydrogen breath test.

Characteristics of FHBT-positive vs FHBT-negative cases

FHBT parameters among cases: Baseline breath hydrogen and methane levels were similar between FHBT-positive and FHBT-negative cases. As expected, peak breath hydrogen and methane levels were significantly higher in the FHBT-positive group. The total number of patients who developed symptoms during FHBT did not differ significantly between the two groups (P = 0.14) (Table 2).

Table 2 Characteristics of the fructose hydrogen breath test among cases, n (%)/median (range).

S. No	Parameters	FHBT positive (n = 20)	FHBT negative (n = 50)	P value
1	FHBT - baseline H2	6 (0-14)	6 (0-12)	0.70
2	FHBT - peak H2	37 (22-124)	8 (0-27)	< 0.01
3	Methane - baseline	2 (1-9)	2 (1-16)	0.24
4	Methane - peak	4 (1-13)	3 (1-26)	< 0.01
5	Methane producers (CH4 ≥ 3)	8 (40)	24 (48)	0.54
6	Symptoms during FHBT	16 (80)	31 (62)	0.14

FHBT: Fructose hydrogen breath test.

Predictors of FM: In the univariate analysis, FHBT-positive patients were significantly younger, with a median age of 26.5 years, compared to 36 years in FHBT-negative patients (P = 0.01). FHBT-positive cases were predominantly female (15/20, 75%) compared to FHBT-negative cases (19/50, 38%) (P = 0.01). A baseline Bristol Stool Form Scale score > 4 was present in 5/20 (25%) FHBT-positive cases vs 3/50 (6%) FHBT-negative cases (P = 0.02). The severity of bloating was comparable between the two groups in this study. There were no statistically significant differences in symptom duration, dietary patterns, BMI distribution, or use of proton pump inhibitors or promotility drugs in the preceding four weeks between the two groups (Table 3).

Table 3 Univariate analysis of conditions and symptoms associated with the detection of fructose malabsorption by a fructose breath test, n (%)/median (range).

Characteristics	FHBT positive (n = 20)	FHBT negative (n = 50)	P value
Age (years)	26.5 (19-74)	36 (18-65)	0.01
Gender	Females: 15 (75)	Females: 19 (38)	0.01
Duration of symptoms (years)	2 (1-15)	2 (1-10)	0.69
BMI (kg/m2)	21.3 (12.5-26.6)	22.4 (15.6-31.2)	0.25
Dietary pattern	Mixed: 13 (65)	Mixed: 39 (78)	0.26
Bristol score (> 4)	5 (25)	3 (6)	0.26
Severity of bloating (severe)	9 (45)	12 (24)	0.20
PPI usage	16 (80)	47 (94)	0.07
Prokinetics	8 (40)	13 (26)	0.24
Abdominal distension	19 (95)	49 (98)	1.0
Belching	1 (5)	5 (10)	0.50
Flatulence	1 (5)	1 (2)	0.49
Nausea	3 (15)	3 (6)	0.22
Abdominal pain	2 (10)	5 (10)	1.0
Epigastric discomfort	9 (45)	8 (16)	0.01
Mucus in stools	5 (25)	4 (8)	< 0.05
Constipation	6 (30)	15 (30)	1.00
Loose stools	1 (5)	3 (6)	0.86

FHBT: Fructose hydrogen breath test; BMI: Body mass index; PPI: Proton pump inhibitor.

Among the baseline gastrointestinal symptoms, only epigastric discomfort (FHBT-positive: 9/20 vs FHBT-negative: 8/50; P = 0.01) and mucus in stools (FHBT-positive: 5/20 vs FHBT-negative: 4/50; P < 0.05) were significantly more prevalent in the FHBT-positive group. The incidence of abdominal distension, flatulence, belching, nausea, abdominal pain, constipation, and loose stools did not differ significantly between the two groups (Table 3). However, in the multivariate logistic regression analysis, female sex was the only independent predictor of FM (P = 0.02).

DISCUSSION

The pathophysiology of FABD is complex and poorly understood. Several factors, such as an altered gut-brain axis, impaired abdominal emptying, abnormal intraluminal content, altered intestinal gas handling, visceral hypersensitivity, and changes in the intestinal microbiome may contribute to abdominal bloating and distension[19-21]. Dietary factors, particularly those high in osmolarity and poorly absorbable, such as fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs), lactulose, and fructose, can exacerbate IBS symptoms[20]. In our case-control study, FM was present in approximately one-third of patients with functional bloating (29%), a significantly higher proportion than in healthy controls (3%). Female sex was the only independent predictor of FM in the multivariate analysis. Notably, a substantial proportion of study participants experienced symptoms during FHBT (35/84; 42%) without objective evidence of FM, highlighting fructose intolerance as a distinct entity from FM.

In our study, FM was detected in only 1 of the 35 healthy controls (3%). Sharma et al[12] also reported a similar FM prevalence (2.4%) among healthy controls in their study on FM in IBS, using a 25 g fructose load and a positivity threshold (> 20 ppm above baseline) in the Indian subpopulation. Notably, this is much lower than the reported prevalence of FM (22.9%) by Jung et al[8] in healthy Korean controls in their study on FM in IBS with 25 g fructose.

The prevalence of FM in our study (29%) among patients with functional bloating differed from that reported by Fernández-Bañares et al[18], the only previous study to examine sugar malabsorption in functional bloating. They found sugar malabsorption in 72.2% of patients, fructose and sorbitol malabsorption in 33% of patients, and both lactose and fructose-plus-sorbitol malabsorption in 22% of patients[18]. However, direct comparisons are limited because of key methodological differences. They used a combined fructose-plus-sorbitol load rather than fructose alone, enrolled only patients with concomitant gas-related symptoms, and did not exclude patients with SIBO prior to breath testing, all of which likely inflated the reported prevalence. Wilder-Smith et al[22] in a larger cohort of FGID patients (n = 1372), including those with functional bloating (n = 109), reported FM in 41.8% of patients with functional bloating[22]. The higher estimate than ours may be due to the larger fructose load of 35 g (vs 25 g) used in their study.

Studies have shown that healthy, asymptomatic individuals can typically absorb up to 25 g of fructose[23]. Increasing the fructose dose to 50 g often overwhelms the digestive capacity of healthy participants, leading to high false-positive rates, whereas doses lower than 25 g fructose will have high false-negative rates[8]. Previous studies have shown that 50 g of fructose causes symptoms in up to 50% of healthy participants, whereas a 25 g dose elicited positive results in only 10%-20% of asymptomatic participants[8,23]. Based on this rationale, the North American consensus conference recommended a 25 g dose for fructose breath tests rather than higher doses to improve diagnostic specificity[24]. The role of FM has mostly been studied in patients with IBS. Jung et al[8] used a methodology similar to ours, with prior SIBO exclusion and 25 g fructose load, and reported FM in 45.7% of IBS patients. Choi et al[25] reported FM in 38% (31/80) of patients with suspected IBS using the ROME II criteria. Sharma et al[12] reported FM in 14.4% of Indian patients with IBS, which is among the lowest reported rates globally. The authors attributed this to the low dietary fructose intake in the Indian subpopulation. Wilder-Smith et al[22] showed that FM prevalence was comparable across all FGID subgroups: 42.4% in IBS, 41.6% in FD, and 41.8% in functional bloating[22]. This suggests that FM is a transdiagnostic contributor to the FGID spectrum rather than being specific to individual diagnoses.

In our study, 42% of participants with negative FHBT results had symptoms during testing, suggesting fructose intolerance. This dissociation between malabsorption and intolerance has been previously reported. In the study by Wilder-Smith et al[22], clinical gastrointestinal symptoms were significantly correlated with symptoms produced during breath testing (P < 0.0001), but not with malabsorption. Moreover, adequate symptomatic relief with dietary adaptation has been observed, irrespective of the presence of malabsorption[22]. In a double-blind randomized crossover study, they showed that plasma fructose and fructose metabolite concentrations were similar between patients with and without fructose intolerance in FGID; symptoms did not correlate significantly with blood fructose concentration, suggesting that gut microbiota or visceral hypersensitivity may play a greater role in symptom generation than malabsorption[26]. Melchior et al[27] also showed that an abnormal fructose breath test is not a reliable predictor of symptomatic response to a low-fructose diet, calling into question the sole reliance on breath testing for clinical decision-making[27]. These findings suggest that FHBT is useful for detecting malabsorption but may underestimate the clinical burden of fructose-related symptoms, and that symptom provocation during the test may carry independent clinical value.

Methane significantly contributes to functional abdominal bloating by acting as a gaseous neurotransmitter that delays intestinal transit, leading to constipation and gas buildup[28]. High methane levels, usually generated by anaerobic archaea such as Methanobrevibacter smithii, are closely associated with constipation-predominant IBS and intestinal methanogen overgrowth[29,30]. Despite this pathophysiological mechanism, studies have shown that low methane producers have significantly increased bloating and cramping after ingesting sorbitol and fiber[31,32]. In our study, methane producers were not significantly different between the FHBT-positive and-negative groups (40% vs 48%) and between cases and controls, although their role in symptom modulation in functional bloating warrants further study.

In the univariate analysis, younger age, female sex, Bristol Stool Scale score > 4, and baseline symptoms of epigastric discomfort and stool mucus were significantly associated with FM. However, in the multivariate analysis, female sex was the only independent predictor of FM. In our cohort, FM was predominantly observed in women (15/20; 75%), suggesting a possible sex-related predisposition. Sex hormones play a central role in amplifying functional abdominal bloating in women. Previous studies have demonstrated that FGIDs are more common in women, possibly due to the influence of sex hormones on gastrointestinal motility, visceral sensitivity, and the gut-brain axis[33,34]. Estrogen and progesterone influence intestinal motility, visceral pain perception, and neuroimmune interactions within the gut-brain axis, which may contribute to the higher prevalence of functional gastrointestinal symptoms in females[35-37]. Progesterone-mediated smooth muscle relaxation delays intestinal transit and promotes gas retention, whereas estrogen alters serotonergic signalling, enhancing visceral hypersensitivity[38]. The diminished significance of younger age, Bristol Stool Scale score > 4, epigastric discomfort, and mucus in stools in the multivariate analysis likely reflects the small sample size of the FM-positive subgroup, which may have limited our ability to identify independent associations.

This study had several notable strengths. To our knowledge, this is the first study from India to systematically assess the pathophysiology of functional bloating, with a specific focus on fructose malabsorption. Furthermore, this is only the second study worldwide to examine FM in patients with functional bloating. Unlike an earlier study, our research used a case-control design that enhanced the validity of the results. The study also employed a rigorous methodological approach, including age- and sex-matched controls and a sufficient sample size, enabling a more reliable evaluation of the association between FM and functional bloating in patients with IBS. Additionally, SIBO was ruled out using a GHBT, thereby reducing the risk of false-positive FHBT results and improving the diagnostic accuracy for FM in the study population.

This study had a few limitations. This study used the Rome III criteria to diagnose functional bloating. The Rome IV criteria employ stricter diagnostic definitions and symptom frequency thresholds. Therefore, the use of the Rome III criteria may have resulted in the inclusion of a broader spectrum of patients, potentially affecting the generalizability of the findings to populations defined by the Rome IV criteria. FHBT was performed over three hours, whereas Melchior et al[10] used a five-hour testing period, allowing the detection of approximately 10% more cases of fructose malabsorption. Shorter protocols may miss delayed hydrogen peaks, leading to false-negative results and an underestimation of FM[39]. Similarly, Wilder-Smith et al[22] showed that 16% of fructose intolerance cases would have been missed with a 3-hour test duration. Additionally, fructose was administered alone during the breath test, which may not accurately reflect the typical dietary conditions in which fructose is usually consumed with glucose. Glucose aids in fructose absorption and may affect breath test outcomes. The sample size was modest, with only 20 patients positive for FHBT; therefore, the risk of overfitting in the multivariable analysis must be considered. Furthermore, bloating has a multifactorial etiology and is associated with many functional and organic GI conditions, which were not entirely ruled out. Patients with alarm symptoms should be thoroughly evaluated for organic causes of bloating, including GI malignancies. Among functional disorders, FM should be considered only after excluding more common causes of bloating, such as constipation, irritable bowel syndrome with visceral hypersensitivity, lactose intolerance, and SIBO. The most practical diagnostic approach is a careful dietary history, followed by a therapeutic trial of a low-FODMAP or fructose-restricted diet with symptom reassessment. The inherent limitations of the hydrogen breath test include variable diagnostic performance, low sensitivity and specificity, and false negatives in non-hydrogen producers, which can reduce reliability. Although SIBO has been excluded by the GHBT, evidence shows that SIBO is frequently associated with bloating[40]. In SIBO, excess bacteria metabolize carbohydrates before absorption, producing gases such as hydrogen, methane, and carbon dioxide. This leads to luminal gas accumulation, abdominal distension, borborygmi, flatulence, and discomfort. SIBO may cause bloating through altered intestinal motility, visceral hypersensitivity, low-grade inflammation, and disrupted gut-brain signalling, so symptoms can be disproportionate to the amount of gas. FM may be overdiagnosed if SIBO and intestinal methanogen overgrowth are not properly evaluated, as these disorders can present with overlapping symptoms. Finally, follow-up of patients diagnosed with FM after dietary interventions, such as a FODMAP-restricted diet, was not conducted in this study. Future research evaluating clinical outcomes after dietary modifications will help clarify the therapeutic importance of identifying FM in patients with functional bloating.

CONCLUSION

In this case-control study, FM was identified in approximately one-third of patients with functional abdominal bloating, which was significantly higher than that in healthy controls. A substantial proportion of patients without FM also developed gastrointestinal symptoms during fructose HBT, suggesting a clinically relevant association beyond FM and bloating. Female sex was an independent predictor of fructose malabsorption. These findings suggest that FM should be evaluated in patients with unexplained functional abdominal bloating, particularly in female patients. High fructose content in foods and FM may be important and potentially modifiable factors in patients presenting with functional abdominal bloating. Future studies are needed to define the role of FODMAP-restricted diets in the management of functional bloating.