Effects of fiber intake on intestinal pH, transit, and predicted oral mesalamine delivery in patients with ulcerative colitis

Letter: Light in the lumen-The expanding role of intestinal ultrasound for functional symptoms in inflammatory bowel disease

This article is linked to Aliu et al papers. To view these articles, visit https://doi.org/10.1111/apt.17988 and https://doi.org/10.1111/apt.18196

Revolution in diet therapy for inflammatory bowel disease

Until recently, diet as a therapeutic tool to treat inflammatory bowel disease (IBD) has not been proven effective. Nearly a century in the making we are in the grips of a revolution in diet therapies for IBD, driven by emerging data revealing diet as a key environmental factor associated with IBD susceptibility, and observational studies suggesting that dietary intake may play a role in the disease course of established IBD. This review summarizes the current evidence for diets trialed as induction and maintenance therapy for IBD. For Crohn's disease, exclusive enteral nutrition and the Crohn's disease exclusion diet with partial enteral nutrition are supported by emerging high-quality evidence as induction therapy, but are short-term approaches that are not feasible for prolonged use. Data on diet as maintenance therapy for Crohn's disease are conflicting, with some studies supporting fortification, and others suppression, of certain food components. For ulcerative colitis, data are not as robust for diet as induction and maintenance therapy; however, consistent themes are emerging, suggesting benefits for diets that are plant-based, high in fiber and low in animal protein. Further studies for both Crohn's disease and ulcerative colitis are eagerly awaited, which will allow specific recommendations to be made. Until this time, recommendations default to population based healthy eating guidelines.

Meta-analysis: Intestinal ultrasound to evaluate colonic contents and constipation

BACKGROUND

Constipation can be diagnosed clinically using the Rome criteria. Ultrasound (US), which lacks the radiation exposure of conventional X-ray, holds promise as a non-invasive tool to evaluate colonic contents and constipation.

AIM

To examine the role of US in the assessment of constipation.

METHODS

We performed a systematic search of Embase (OVID, 1984), Medline (Ovid, 1946), Cochrane Central, ClinicalTrials.gov and Australia New Zealand Clinical Trials Registry from database inception to 26 January 2024 according to PRISMA guidelines and prospectively registered with PROSPERO. All studies using US to assess constipation or colonic contents in either adults or children were included. Rectal diameter measurements were pooled in meta-analysis. Risk of bias was assessed using the Newcastle Ottawa Scales and Joanna Briggs Institute checklists.

RESULTS

Of 12,232 studies screened, 51 articles (6084 patients; 3422 children) describing US to assess symptoms in patients with constipation were included. Most studies used Rome criteria to diagnose constipation. Rectal diameter was associated with clinical constipation in 29 paediatric studies (3331 patients). Meta-analysis showed the mean rectal diameter of constipated patients was significantly higher than controls (mean difference 12 mm, 95% confidence intervals (CI): 6.48, 17.93, p < 0.0001, n = 16 studies). Other features of constipation on US included posterior acoustic shadowing and echogenicity of luminal contents.

CONCLUSION

US is an appealing imaging modality to assess luminal contents and constipation. Further well-designed studies are required to validate US metrics that accurately identify constipation.

Bicarbonate secretion and acid/base sensing by the intestine

The transport of bicarbonate across the enterocyte cell membrane regulates the intracellular as well as the luminal pH and is an essential part of directional fluid movement in the gut. Since the first description of "active" transport of HCO3- ions against a concentration gradient in the 1970s, the fundamental role of HCO3- transport for multiple intestinal functions has been recognized. The ion transport proteins have been identified and molecularly characterized, and knockout mouse models have given insight into their individual role in a variety of functions. This review describes the progress made in the last decade regarding novel techniques and new findings in the molecular regulation of intestinal HCO3- transport in the different segments of the gut. We discuss human diseases with defects in intestinal HCO3- secretion and potential treatment strategies to increase luminal alkalinity. In the last part of the review, the cellular and organismal mechanisms for acid/base sensing in the intestinal tract are highlighted.

Single-strain behavior predicts responses to environmental pH and osmolality in the gut microbiota

Changes to gut environmental factors such as pH and osmolality due to disease or drugs correlate with major shifts in microbiome composition; however, we currently cannot predict which species can tolerate such changes or how the community will be affected. Here, we assessed the growth of 92 representative human gut bacterial strains spanning 28 families across multiple pH values and osmolalities in vitro. The ability to grow in extreme pH or osmolality conditions correlated with the availability of known stress response genes in many cases, but not all, indicating that novel pathways may participate in protecting against acid or osmotic stresses. Machine learning analysis uncovered genes or subsystems that are predictive of differential tolerance in either acid or osmotic stress. For osmotic stress, we corroborated the increased abundance of these genes in vivo during osmotic perturbation. The growth of specific taxa in limiting conditions in isolation in vitro correlated with survival in complex communities in vitro and in an in vivo mouse model of diet-induced intestinal acidification. Our data show that in vitro stress tolerance results are generalizable and that physical parameters may supersede interspecies interactions in determining the relative abundance of community members. This study provides insight into the ability of the microbiota to respond to common perturbations that may be encountered in the gut and provides a list of genes that correlate with increased ability to survive in these conditions. IMPORTANCE To achieve greater predictability in microbiota studies, it is crucial to consider physical environmental factors such as pH and particle concentration, as they play a pivotal role in influencing bacterial function and survival. For example, pH is significantly altered in various diseases, including cancers, inflammatory bowel disease, as well in the case of over-the-counter drug use. Additionally, conditions like malabsorption can affect particle concentration. In our study, we investigate how changes in environmental pH and osmolality can serve as predictive indicators of bacterial growth and abundance. Our research provides a comprehensive resource for anticipating shifts in microbial composition and gene abundance during complex perturbations. Moreover, our findings underscore the significance of the physical environment as a major driver of bacterial composition. Finally, this work emphasizes the necessity of incorporating physical measurements into animal and clinical studies to better understand the factors influencing shifts in microbiota abundance.

Gaseous metabolites as therapeutic targets in ulcerative colitis

Diet therapies are currently under-utilised in optimising clinical outcomes for patients with active ulcerative colitis (UC). Furthermore, existing dietary therapies are framed by poorly defined mechanistic targets to warrant its success. There is good evidence to suggest that microbial production of gaseous metabolites, hydrogen sulfide (H₂S) and nitric oxide (NO) are implicated in the development of mucosal inflammation in UC. On a cellular level, exposure of the colonic epithelium to excessive concentrations of these gases are shown to promote functional defects described in UC. Hence, targeting bacterial production of these gases could provide an opportunity to formulate new dietary therapies in UC. Despite the paucity of evidence, there is epidemiological and clinical data to support the concept of reducing mucosal inflammation in UC via dietary strategies that reduce H₂S. Several dietary components, namely sulphur-containing amino acids and inorganic sulphur have been shown to be influential in enhancing colonic H₂S production. More recent data suggests increasing the supply of readily fermentable fibre as an effective strategy for H₂S reduction. Conversely, very little is known regarding how diet alters microbial production of NO. Hence, the current evidence suggest that a whole diet approach is needed. Finally, biomarkers for assessing changes in microbial gaseous metabolites in response to dietary interventions are very much required. In conclusion, this review identifies a great need for high quality randomised-controlled trials to demonstrate the efficacy of a sulphide-reducing dietary therapy for patients with active UC.

Acute effect of Melon Manis Terengganu peel powder on glycemic response, perceived satiety, and food intake: a randomized, placebo-controlled crossover trial in adults at risk of type 2 diabetes

BACKGROUND

Melon Manis Terengganu (MMT) peel has a high dietary fiber content, but there is no data examining its health benefits in adults at risk of type 2 diabetes. The objective of the study was to evaluate whether consumption of MMT peel powder improves glycemic response, satiety, and food intake in adults at risk of type 2 diabetes.

METHODS

An open-label, randomized, placebo-controlled, crossover design trial was conducted among adults (n = 30, ages 18-59 y) at risk of type 2 diabetes. They consumed Formulation 3 (formulated MMT peel powder) [A] and control (glucose) [B] with study breakfast based on randomly assigned treatment sequences (AB, BA) established by Research Randomizer ( www.randomizer.org ). Capillary blood glucose and perceived satiety were determined at baseline (0 min), 30, 60, 90 and 120 min, followed by a post-intervention food intake measurement.

RESULTS

The repeated measures analysis of variance (ANOVA) revealed significant time (F = 84.37, p <  0.001, η_p² = 0.744), condition (F = 22.89, p <  0.001, η_p² = 0.441), and time*condition effects (F = 24.40, p <  0.001, η_p² = 0.457) in blood glucose levels. Respondents (n = 30) who consumed Formulation 3 also had a significantly lower blood glucose 2-hour incremental area under the curve (iAUC) of 134.65 ± 44.51 mmol/L*min and maximum concentration (CMax) of 7.20 (7.10, 8.20) mmol/L with relative reduction of 26.8 and 13.3% respectively, when compared with control (p <  0.001). Besides, significantly greater perceived satiety, lower energy and fat intake as well as higher dietary fiber intake were also observed in the intervention group compared with the placebo group (p <  0.05). There were no marked side effects associated with the ingestion of the test products.

CONCLUSIONS

Short-term consumption of formulated MMT peel powder may improve glycemic response, increase perceived satiety and reduce food intake in adults at risk of type 2 diabetes with the potential to be utilized as a functional beverage. Medium-to long-term clinical trial is warranted to determine whether taking this formulated MMT peel powder on a daily basis has an influence on health outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT05298111. Registered 28/03/2022.

Effects of a low FODMAP diet on the colonic microbiome in irritable bowel syndrome: a systematic review with meta-analysis

BACKGROUND

A low fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAP) diet is increasingly used to manage symptoms in irritable bowel syndrome (IBS). Although this approach may alter the colonic microbiome, the nature of these changes has not been comprehensively synthesized.

OBJECTIVES

The aim of this study was to conduct a systematic review with meta-analysis of randomized controlled trials examining the impact of a low FODMAP diet on the composition and function of the microbiome in patients with IBS.

METHODS

A systematic search was conducted for randomized controlled trials evaluating the effects of a low FODMAP diet on the colonic microbiome in patients with IBS in MEDLINE, EMBASE, CENTRAL, and Web of Science from inception to April 2022. Outcomes included diversity of the microbiome, specific bacterial abundances, fecal SCFA concentration, and fecal pH. For fecal SCFA concentrations and pH, meta-analyses were performed via a random-effects model.

RESULTS

Nine trials involving 403 patients were included. There were no clear effects of the low FODMAP diet on diversity of the microbiome. A low FODMAP diet consistently led to lower abundance of Bifidobacteria, but there were no clear effects on diversity of the microbiome or abundances of other specific taxa. There were no differences in total fecal SCFA concentration between the low FODMAP diet and control diets (standardized mean difference: -0.25; 95% CI: -0.63, 0.13; P = 0.20), nor were there differences for fecal concentrations of specific SCFAs or fecal pH.

CONCLUSIONS

In patients with IBS, the effects of a low FODMAP diet on the colonic microbiome appear to be specific to Bifidobacteria with no consistent impacts on other microbiome metrics, including diversity, fecal SCFA concentrations, and fecal pH. Further, adequately powered trials are needed to confirm these findings.This review was registered at https://www.crd.york.ac.uk/prospero/ as CRD42020192243.