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Gut Microbial Metabolites and Biochemical Pathways Involved in Irritable Bowel Syndrome: Effects of Diet and Nutrition on the Microbiome.
James, SC, Fraser, K, Young, W, McNabb, WC, Roy, NC
The Journal of nutrition. 2020;(5):1012-1021
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Abstract
The food we consume and its interactions with the host and their gut microbiota affect normal gut function and health. Functional gut disorders (FGDs), including irritable bowel syndrome (IBS), can result from negative effects of these interactions, leading to a reduced quality of life. Certain foods exacerbate or reduce the severity and prevalence of FGD symptoms. IBS can be used as a model of perturbation from normal gut function with which to study the impact of foods and diets on the severity and symptoms of FGDs and understand how critical processes and biochemical mechanisms contribute to this impact. Analyzing the complex interactions between food, host, and microbial metabolites gives insights into the pathways and processes occurring in the gut which contribute to FGDs. The following review is a critical discussion of the literature regarding metabolic pathways and dietary interventions relevant to FGDs. Many metabolites, for example bile acids, SCFAs, vitamins, amino acids, and neurotransmitters, can be altered by dietary intake, and could be valuable for identifying perturbations in metabolic pathways that distinguish a "normal, healthy" gut from a "dysfunctional, unhealthy" gut. Dietary interventions for reducing symptoms of FGDs are becoming more prevalent, but studies investigating the underlying mechanisms linked to host, microbiome, and metabolite interactions are less common. Therefore, we aim to evaluate the recent literature to assist with further progression of research in this field.
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The role of bile acids in the pathogenesis of bowel diseases.
Panek-Jeziorna, M, Mulak, A
Postepy higieny i medycyny doswiadczalnej (Online). 2017;(1):737-746
Abstract
Bile acids not only play a cardinal role in the digestion and absorption of fat and fat-soluble vitamins, but also significantly affect gastrointestinal motor, sensory and secretory functions, intestinal barrier permeability and the regulation of the inflammatory response. The results of recent studies have revealed complex interactions between bile acids and the gut microbiota. In addition, bile acids also play a role of signaling molecules regulating the activity of lipid and glucose metabolic pathways, as well as a role of ligands for transcription factors. Genetic factors associated with the regulation of bile acid synthesis, transport and action may significantly influence gastrointestinal function and predispose to diarrhea resulting from bile acid malabsorption. Methods used in the diagnosis of bile acid malabsorption include 75selenium-homotaurocholic acid test, serum C4 and fibroblast growth factor 19 (FGF19), as well as fecal bile acid levels. The paper presents the latest data on the role of bile acid in the pathogenesis of irritable bowel syndrome, inflammatory bowel diseases and colorectal cancer. Advances in the treatment of disturbances in bile acids absorption and synthesis are also presented. A better understanding of molecular mechanisms regulating bile acid action may have implication for colorectal cancer prevention.
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Irritable bowel syndrome and diet: where are we in 2018?
Dimidi, E, Rossi, M, Whelan, K
Current opinion in clinical nutrition and metabolic care. 2017;(6):456-463
Abstract
PURPOSE OF REVIEW The aim is to review the most recent advances in the evidence supporting the use of various dietary interventions for the management of irritable bowel syndrome (IBS). RECENT FINDINGS There is insufficient evidence of the effect of fibres other than psyllium in IBS, whereas the recent studies on prebiotics suggest a limited effect in IBS. Recent probiotic trials continue to provide varying results, with some probiotic strains exhibiting beneficial effects, whereas others show no effect. Recent trials have also confirmed the clinical effectiveness of a diet low in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (i.e. low FODMAP diet) in IBS. Although gluten sensitivity has also been recently investigated, its presence cannot be confirmed yet because of the presence of other potential contributing compounds in wheat. Studies also suggest a potential beneficial effect of peppermint oil, which warrants further research. SUMMARY It is clear that a low FODMAP diet has a beneficial effect in a majority of patients with IBS. Probiotics also have great potential in the management of IBS; however, it is still unclear which strains and doses are the most beneficial. Further research is needed on the effect of different fibres, or combinations of fibres, in IBS.
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Serotonergic reinforcement of intestinal barrier function is impaired in irritable bowel syndrome.
Keszthelyi, D, Troost, FJ, Jonkers, DM, van Eijk, HM, Lindsey, PJ, Dekker, J, Buurman, WA, Masclee, AA
Alimentary pharmacology & therapeutics. 2014;(4):392-402
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Abstract
BACKGROUND Alterations in serotonergic (5-HT) metabolism and/or intestinal integrity have been associated with irritable bowel syndrome (IBS). AIMS To assess the effects of the precursor of 5-HT, 5-hydroxytryptophan (5-HTP), on mucosal 5-HT availability and intestinal integrity, and to assess potential differences between healthy controls and IBS patients. METHODS Fifteen IBS patients and 15 healthy volunteers participated in this randomised double-blind placebo-controlled study. Intestinal integrity was assessed by dual-sugar test and by determining the mucosal expression of tight junction proteins after ingestion of an oral bolus of 100 mg 5-HTP or placebo. Mucosal serotonergic metabolism was assessed in duodenal biopsy samples. RESULTS 5-HTP administration significantly increased mucosal levels of 5-HIAA, the main metabolite of 5-HT, in both healthy controls (7.1 ± 1.7 vs. 2.5 ± 0.7 pmol/mg, 5-HTP vs. placebo, P = 0.02) and IBS patients (20.0 ± 4.8 vs. 8.1 ± 1.3 pmol/mg, 5-HTP vs. placebo, P = 0.02), with the latter group showing a significantly larger increase. Lactulose/L-rhamnose ratios were significantly lower after administration of 5-HTP (P < 0.05) in healthy controls and were accompanied by redistribution of zonula occludens-1 (ZO-1), pointing to reinforcement of the barrier. In IBS, expression of the tight junction proteins was significantly lower compared to healthy controls, and 5-HTP resulted in a further decrease in occludin expression. CONCLUSIONS Oral 5-HTP induced alterations in mucosal 5-HT metabolism. In healthy controls, a reinforcement of the intestinal barrier was seen whereas such reaction was absent in IBS patients. This could indicate the presence of a serotonin-mediated mechanism aimed to reinforce intestinal barrier function, which seems to dysfunction in IBS patients.
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The role of FODMAPs in irritable bowel syndrome.
Shepherd, SJ, Halmos, E, Glance, S
Current opinion in clinical nutrition and metabolic care. 2014;(6):605-9
Abstract
PURPOSE OF REVIEW Irritable bowel syndrome (IBS) is a condition affecting approximately 10-15% of Western populations. The Rome III criteria are applied to many studies to validate the diagnosis of IBS. The low fermentable oligo, di, monosaccharides and polyol (FODMAP) diet has been the subject of many robust clinical trials and is now used as the primary dietary therapy internationally. This review examines the current evidence for the role of the low FODMAP diet in IBS. RECENT FINDINGS Detailed commentary on original research involving FODMAPs and IBS symptoms from 2013 to 2014 is provided. SUMMARY The low FODMAP diet has been shown to be an efficacious therapy for reduction of functional gastrointestinal symptoms seen in IBS. Recent publications provide randomized controlled trial and prospective observational evidence in support of the diet for symptom management. The low FODMAP diet appears to be superior to a gluten-free diet in people with self-reported nonceliac gluten sensitivity. Although the low FODMAP diet has not been shown to reduce the prebiotic effect in the colon, total colonic bacterial load was reduced. Further research investigating the potential health implications of both this and the nutritional adequacy of the liberalized low FODMAP diet is required.