Prevalence of Fructose Malabsorption in Patients With Irritable Bowel Syndrome After Excluding Small Intestinal Bacterial Overgrowth

Food Intolerances, Food Allergies and IBS: Lights and Shadows

This narrative review delves into the intricate relationship between irritable bowel syndrome (IBS) and food intolerances. IBS, a chronic functional gastrointestinal disorder, is characterized by symptoms like abdominal pain and altered bowel habits. The prevalence of IBS has increased globally, especially among young adults. Food and dietary habits play a crucial role in IBS management. About 85-90% of IBS patients report symptom exacerbation linked to specific food consumption, highlighting the strong connection between food intolerances and IBS. Food intolerances often exhibit a dose-dependent pattern, posing a challenge in identifying trigger foods. This issue is further complicated by the complex nature of gastrointestinal physiology and varying food compositions. This review discusses various dietary patterns and their impact on IBS, including the low-FODMAP diet, gluten-free diet, and Mediterranean diet. It highlights the importance of a personalized approach in dietary management, considering individual symptom variability and dietary history. In conclusion, this review emphasizes the need for accurate diagnosis and holistic management of IBS, considering the complex interplay between dietary factors and gastrointestinal pathophysiology. It underlines the importance of patient education and adherence to treatment plans, acknowledging the challenges posed by the variability in dietary triggers and the psychological impact of dietary restrictions.

Gene variants of the SLC2A5 gene encoding GLUT5, the major fructose transporter, do not contribute to clinical presentation of acquired fructose malabsorption

Background

While role of ALDOB-related gene variants for hereditary fructose intolerance is well established, contribution of gene variants for acquired fructose malabsorption (e.g. SLC2A5, GLUT5) is not well understood.

Methods

Patients referred to fructose breath test were further selected to identify those having acquired fructose malabsorption. Molecular analysis of genomic DNA included (I) exclusion of 3 main ALDOB gene variants causing hereditary fructose intolerance and (II) sequencing analysis of SLC2A5 gene comprising complete coding region, at least 20 bp of adjacent intronic regions and 700 bp of proximal promoter.

Results

Among 494 patients, 35 individuals with acquired fructose malabsorption were identified based on pathological fructose-breath test and normal lactose-breath test. Thirty four of them (97%) had negative tissue anti-transglutaminase and/or deamidated gliadin antibodies in their medical records. Molecular analysis of SLC2A5 gene of all 35 subjects identified 5 frequent and 5 singular gene variants mostly in noncoding regions (promoter and intron). Allele frequencies of gene variants were similar to those reported in public databases strongly implying that none of them was associated with acquired fructose malabsorption.

Conclusions

Gene variants of coding exons, adjacent intronic regions and proximal promoter region of SLC2A5 gene are unlikely to contribute to genetic predisposition of acquired fructose malabsorption.

A systematic review and meta-analysis on the prevalence of non-malignant, organic gastrointestinal disorders misdiagnosed as irritable bowel syndrome

Treatable gastrointestinal disorders in patients with symptoms typical for irritable bowel syndrome (IBS) may be overlooked. The prevalence of five gastrointestinal conditions—bile acid diarrhoea (BAD), carbohydrate malabsorption (CM), microscopic colitis (MC), pancreatic exocrine insufficiency (PEI) and small intestinal bacterial overgrowth (SIBO) was systematically assessed from studies including consecutive patients meeting diagnostic criteria for IBS. 4 databases were searched from 1978 to 2020. Studies were included if they evaluated the prevalence of these conditions in secondary healthcare setting. Estimated pooled rates were calculated and statistical heterogeneity between studies was evaluated using Q and I² statistics. Seven studies (n = 597) estimated the pooled prevalence for BAD as 41% (95% CI 29–54). 17 studies (n = 5068) estimated that of MC as 3% (95% CI 2–4%). Two studies (n = 478) suggested a rate of 4.6% (range: 1.8–6.1%) for PEI. Using breath testing, 26 studies (n = 6700) and 13 studies (n = 3415) estimated the prevalence of lactose and fructose malabsorption as 54% (95% CI 44–64%) and 43% (95% CI 23–62%); 36 studies (n = 4630) and 22 studies (n = 2149) estimated that of SIBO as 49% (95% CI 40–57%) with lactulose and 19% (95% CI 13–27%) with glucose. Rates of all conditions were significantly higher than in healthy controls. A significant proportion of patients presenting to secondary care with IBS have an organic condition which may account for their symptoms. Failure to exclude such conditions will deny patients effective treatment.

Expression of the fructose transporter GLUT5 in patients with fructose malabsorption

BACKGROUND

 Patients with abdominal symptoms are frequently diagnosed with fructose malabsorption (FM). Fructose is absorbed by monosaccharide transporters located in the brush border of the human small intestine. The aim of this study was to investigate the histoanatomical distribution of the main fructose transporter GLUT5.

MATERIALS AND METHODS

 We studied 223 patients diagnosed with FM by a hydrogen breath test and grouped according to their response to a fructose-free diet. The control group were 42 healthy individuals and 29 patients with celiac disease (CD). The fructose breath test was done with 50 g fructose. The expression of Glut5 in duodenal biopsy specimens was studied by immunohistochemistry. The Kruskal-Wallis-test and Mann-Whitney U-test were used to carry out the statistical analysis.

RESULTS

 The histoanatomical expression pattern of GLUT5 did not differ significantly between those patients with FM who responded completely to a fructose-free diet (n = 183) and healthy individuals (n = 42); nor did it correlate to H2 production measured in fructose breath testing. In patients with FM, the GLUT5 expression pattern did not differ between those individuals responding to a fructose-free diet and those who did not. However, GLUT5 expression pattern was significantly different in patients with CD (n = 29) compared to patients with FM and to healthy individuals (p = 0.009).

CONCLUSION

 GLUT5 expression patterns are not be related to adult patients with FM. However, in secondary malabsorption, a decreased GLUT5 expression was found. Further investigation is needed to understand the essential factors in FM and the influence on functional gastrointestinal disorders.

Fructose malabsorption: causes, diagnosis and treatment

This review intends to act as an overview of fructose malabsorption (FM) and its role in the aetiology of diseases including, but not limited to, irritable bowel syndrome (IBS) and infantile colic and the relationship between fructose absorption and the propagation of some cancers. IBS results in a variety of symptoms including stomach pains, cramps and bloating. Patients can be categorised into two groups, depending on whether the patients’ experiences either constipation (IBS-C) or diarrhoea (IBS-D). FM has been proposed as a potential cause of IBS-D and other diseases, such as infantile colic. However, our knowledge of FM is limited by our understanding of the biochemistry related to the absorption of fructose in the small intestine and FM’s relationship with small intestinal bacterial overgrowth. It is important to consider the dietary effects on FM and most importantly, the quantity of excess free fructose consumed. The diagnosis of FM is difficult and often requires indirect means that may result in false positives. Current treatments of FM include dietary intervention, such as low fermentable oligo-, di-, monosaccharides and polyols diets and enzymatic treatments, such as the use of xylose isomerase. More research is needed to accurately diagnose and effectively treat FM. This review is designed with the goal of providing a detailed outline of the issues regarding the causes, diagnosis and treatment of FM.

Fructose Malabsorption in Chilean Children Undergoing Fructose Breath Test at a Tertiary Hospital

Fructose is a highly abundant carbohydrate in western diet and may induce bowel symptoms in children as in adults. The main objective of this study is to describe the frequency of fructose malabsorption (FM) in symptomatic patients 18 years or younger undergoing fructose breath test in a single tertiary center between 2013 and 2018, and to evaluate whether certain symptoms are related to positivity of the test. Out of 273 tests 183 (67%) were compatible with FM. The most frequent pretest symptom in the overall study population was bloating (83%), followed by abdominal pain (73%). Patients with positive test were younger than those with a negative test (median 5 vs 8 years, P < 0.001). In multivariate analysis, which included age, sex, and symptoms (diarrhea, abdominal pain, bloating, nausea), only age <6 years (odds ratio 2.93, 95% confidence interval 1.64-5.23) and absence of nausea (odds ratio = 3.32, 95% confidence interval 1.56-7.05) were associated with FM.

Role of Diet in Diarrhea-predominant Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a chronic condition characterized by abdominal pain associated with altered bowel habits. Patients with IBS often complain of food-related gastrointestinal symptoms. Specifically, those with diarrhea-predominant IBS report a significantly higher effect on quality on life because of food avoidance compared with those with other IBS subtypes. Physicians and patients often use dietary therapies to mitigate IBS symptoms. In the last 10 years, several dietary interventions such as a gluten-free diet, a diet low in fermentable oligosaccharides, disaccharides, monosaccharides, and polyols diets have been studied in several studies. This review summarizes the current literature on the role of diets such as gluten-free diet, low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols diet, and other carbohydrate malabsorption in the pathophysiology and symptom management in patients with diarrhea-predominant IBS.

Diagnostic Utility of Carbohydrate Breath Tests for SIBO, Fructose, and Lactose Intolerance

BACKGROUND

Unexplained bloating, gas, and pain are common symptoms. If routine tests are negative, such patients are often labeled as irritable bowel syndrome.

AIMS

To determine the diagnostic utility of breath tests that assess for small intestinal bacterial overgrowth (SIBO), fructose or lactose intolerance, and the predictive value of symptoms.

METHODS

Patients with gas, bloating, diarrhea, abdominal pain (≥ 6 months), and negative endoscopy and radiology tests were assessed with symptom questionnaires, glucose (75 g), fructose (25 g), or lactose (25 g) breath tests. Breath tests were categorized as positive when H₂ (≥ 20 ppm) or CH₄ (≥ 15 ppm) increased above baseline values or as hypersensitive when symptoms changed significantly without rise in H₂/CH₄ or as negative.

RESULTS

1230 patients (females = 878) underwent 2236 breath tests. The prevalence of SIBO was 33% (294/883), fructose intolerance was 34% (262/763), and lactose intolerance was 44% (260/590). Hypersensitivity was found in 16% and 9%, respectively, during fructose and lactose breath tests. Although gas (89%), abdominal pain (82%), and bloating (82%) were highly prevalent, pretest symptoms or their severity did not predict an abnormal breath test, but symptoms during the breath test facilitated diagnosis of SIBO, fructose, and lactose intolerance and hypersensitivity.

CONCLUSIONS

Approximately 45% of patients with unexplained gas and bloating had SIBO, fructose, or lactose intolerance; another 9-16% had visceral hypersensitivity. Pretest symptoms were poor predictors, but symptoms during the breath tests were useful. Breath tests are safe, provide significant diagnostic yield, and could be useful in routine gastroenterology practice.

Fructose and irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic disorder characterised by recurrent abdominal pain or discomfort and transit disturbances with heterogeneous pathophysiological mechanisms. The link between food and gastrointestinal (GI) symptoms is often reported by patients with IBS and the role of fructose has recently been highlighted. Fructose malabsorption can easily be assessed by hydrogen and/or methane breath test in response to 25 g fructose; and its prevalence is about 22 % in patients with IBS. The mechanism of fructose-related symptoms is incompletely understood. Osmotic load, fermentation and visceral hypersensitivity are likely to participate in GI symptoms in the IBS population and may be triggered or worsened by fructose. A low-fructose diet could be integrated in the overall treatment strategy, but its role and implication in the improvement of IBS symptoms should be evaluated. In the present review, we discuss fructose malabsorption in adult patients with IBS and the interest of a low-fructose diet in order to underline the important role of fructose in IBS.

The Role of Brain-Derived Neurotrophic Factor in Irritable Bowel Syndrome

Several studies have implied a role of brain-derived neurotrophic factor (BDNF) in abdominal pain modulation in irritable bowel syndrome (IBS). The aim of this study was to establish BDNF protein expression in human colonic biopsies and to show variation in IBS compared to controls. BDNF protein and mRNA levels were correlated with IBS symptom severity based on the IBS-symptom severity score (IBS-SSS). Biopsies from the descending colon and IBS-SSS were obtained from 10 controls and 20 IBS patients. Total protein of biopsies was extracted and assessed by ELISA and Western Blot. Total mRNA was extracted and gene expression measured by nCounter analysis. In IBS patients, symptom severity scores ranged from 124 to 486 (mean ± sem: 314.2 ± 21.2, >300 represents severe IBS) while controls ranged from 0 to 72 (mean ± sem: 27.7 ± 9.0, <75 represents healthy subjects, p < 0.001). IBS patients reported significantly more food malabsorption, former abdominal surgery and psychiatric comorbidities. BDNF protein was present in all samples and did not differ between IBS and controls or sex. Subgroup analysis showed that female IBS patients expressed significantly more BDNF mRNA compared to male patients (p < 0.05) and male IBS-D patients had higher IBS symptom severity scores and lower BDNF mRNA and protein levels compared to male controls (p < 0.05). Scatter plot showed a significant negative correlation between IBS-SSS and BDNF mRNA levels in the cohort of male IBS-D patients and their male controls (p < 0.05). We detected a high proportion of gastrointestinal surgery in IBS patients and confirmed food intolerances and psychiatric diseases as common comorbidities. Although in a small sample, we demonstrated that BDNF is detectable in human descending colon, with higher BDNF mRNA levels in female IBS patients compared to males and lower mRNA and protein levels in male IBS-D patients compared to male controls. Further research should be directed toward subgroups of IBS since their etiologies might be different.

Sex-Gender Differences in Irritable Bowel Syndrome

Because of the sex-gender differences that are shown in a diversity of physiological and psychological factors, it can be speculated that the clinical presentation of symptoms as well as treatment strategies in women and men with irritable bowel syndrome (IBS) may differ. Studies have revealed that IBS is more common in women than men. As for the IBS subtype, IBS with constipation is significantly more prevalent among women than men. Sex hormones and gender differences may play important roles in the pathophysiology of IBS. However, its pathophysiologic mechanisms still remain largely unknown, and therapeutic implications are limited. Moreover, women IBS patients have been reported to feel more fatigue, depression, anxiety, and lower quality of life than men IBS patients. Furthermore, there has been evidence of differences in the appropriate treatment efficacy to IBS in men and women, although relatively few men are enrolled in most relevant clinical trials. A more sex-gender-oriented approach in the medical care setting could improve understanding of heterogeneous patients suffering from IBS. An individualized and multicomponent approach including sex and gender issues might help improve the treatment of IBS.