Effects of a wheat bran extract containing arabinoxylan oligosaccharides on gastrointestinal health parameters in healthy adult human volunteers : a double-blind, randomised, placebo-controlled, cross-over trial

Wheat bran extract (WBE) is a food-grade soluble fibre preparation that is highly enriched in arabinoxylan oligosaccharides. In this placebo-controlled cross-over human intervention trial, tolerance and effects on colonic protein and carbohydrate fermentation were studied. After a 1-week run-in period, sixty-three healthy adult volunteers consumed 3, 10 and 0 g WBE/d for 3 weeks in a random order, with 2 weeks' washout between each treatment period. Fasting blood samples were collected at the end of the run-in period and at the end of each treatment period for analysis of haematological and clinical chemistry parameters. Additionally, subjects collected a stool sample for analysis of microbiota, SCFA and pH. A urine sample, collected over 48 h, was used for analysis of p-cresol and phenol content. Finally, the subjects completed questionnaires scoring occurrence frequency and distress severity of eighteen gastrointestinal symptoms. Urinary p-cresol excretion was significantly decreased after WBE consumption at 10 g/d. Faecal bifidobacteria levels were significantly increased after daily intake of 10 g WBE. Additionally, WBE intake at 10 g/d increased faecal SCFA concentrations and lowered faecal pH, indicating increased colonic fermentation of WBE into desired metabolites. At 10 g/d, WBE caused a mild increase in flatulence occurrence frequency and distress severity and a tendency for a mild decrease in constipation occurrence frequency. In conclusion, WBE is well tolerated at doses up to 10 g/d in healthy adults volunteers. Intake of 10 g WBE/d exerts beneficial effects on gut health parameters

Impact van proteine fermentatie op de darmgezondheid

Dietary and endogenous protein that escape digestion and absorption in the small intestine are fermented by the colonic bacteria to a wide range of metabolites including BCFA, SCFA, ammonia, sulfides, phenolic and indolic compounds. Some of those compounds have been shown to have a toxic capacity in in vitro studies and animal studies. Therefore, protein fermentation is often considered as a risk factor for the development of CRC. However, evidence in humans is currently lacking. Considering the increasing popularity of high protein weight loss diet and the high protein intake associated with our Western-style diet , the aim of this PhD-project was to investigate the role of protein fermentation in gut health. Several randomized controlled studies, with a cross-over or parallel design, were conducted, in which protein fermentation was modulated by changing dietary protein intake or by administering prebiotics. Colonic protein fermentation was evaluated using urinary and fecal markers of protein fermentation, urinary p-cresol concentration and fecal BCFA and p-cresol concentrations. The biomarker lactose-[15N,15N]-ureide was used to study the colonic ammonia metabolism, denaturating gradient gel electrophoresis was applied to study changes in the predominant bacteria and real time PCR to quantify selected bacteria. Fecal metabolite patterns were measured using GC-MS to investigate total colonic fermentation. Fecal water genotoxicity was evaluated using the Comet Assay and fecal water cytotoxicity using the WST-1 assay. The relation between colonic fermentation and gut health was investigated by performing cluster analysis on the fecal metabolite patterns based on fecal water cytotoxicity and genotoxicity. In Chapter 2, we reviewed the literature on the evidence implicating protein fermentation in gut health. Indications on the toxic character of protein fermentation can be found in in vitro and animal studies. However, the available evidence in humans is insufficient to decide on the relevance of protein fermentation in gut health. In Chapter 3 and 4, protein fermentation was modified by changing dietary protein intake. In Chapter 3, normal-weight healthy subjects consumed a high (27%) and low (12%) protein diet isocaloric to their normal protein diet (15%) , while in Chapter 4, a high (30% protein) and standard (15% protein) protein calorie restricted weight loss diet were consumed by overweight subjects. The isocaloric high protein diet successfully stimulated protein fermentation as urinary p-cresol excretion was significantly increased. After the high protein weight loss diet, protein fermentation remained similar to baseline but was higher than after the standard protein weight loss diet. Fecal water genotoxicity and cytotoxicity were not significantly affected by the isocaloric diets or the weight loss diets. In both Chapters 3 and 4, fecal sulfide levels were associated with high genotoxicity. As colonic sulfide-production depends on the presence of sulfate-reducing bacteria, the relation between the number of these bacteria in the colon and the change in fecal water genotoxicity after a high protein diet was further explored in Chapter 5. Increased numbers of sulfate-reducing bacteria correlated with an increase in fecal water genotoxicity after an isocaloric high protein diet, but not after a high protein weight loss diet, suggesting that the combination of sufficient protein intake and high numbers of sulfate-reducing bacteria increase the risk on colonic toxicity. Therefore, high protein diets with high absolute amounts of protein should be discouraged in subjects carrying high numbers of sulfate-reducing bacteria. In Chapters 6 and 7, prebiotics were administered as a strategy to reduce colonic protein fermentation. In Chapter 6, a moderate dose of AXOS (10g/day) was administered, while in Chapter 7, a high dose (30g/day) of AXOS-containing WBE and FOS were compared. In both studies, protein fermentation was reduced after intake of AXOS. The impact of FOS on protein fermentation was less pronounced. In Chapter 6, intake of AXOS induced a decreased urinary ammonia excretion and an increased fecal ammonia excretion, suggesting a reduced exposure of the colonocytes to toxic ammonia, which can be explained by a stimulation of colonic bacterial growth or activity. This functional change was supported by a change in the microbial composition as evidenced by an increase in the numbers of Bifidobacterium adolescentis after AXOS-intake.A high dose of WBE reduced fecal water cytotoxicity, while a moderate dose of AXOS and a high dose of FOS were less effective. None of the prebiotics affected fecal water genotoxicity. Consistent in these two chapters was the finding that prebiotic intake was associated with higher fecal concentrations of cycloalkanes and cycloalkenes. These metabolites were also associated with low cytotoxicity in Chapters 3, 6 and 7. Finally, in Chapter 8, metabolite patterns generated from 4 different sample matrices (urine, feces, fecal water and lyophilized feces) were compared. Metabolite patterns in urine samples were clearly distinct from metabolite patterns in samples originating from feces, which can be attributed to the more important contribution of the host metabolism to the urine metabolome. Also the different fecal sample types displayed distinct metabolite patterns. The impact of prebiotic intake was most pronounced in the fecal metabolome.In conclusion, the results obtained in this PhD-project did not provide evidence for a role of protein fermentation in gut toxicity in healthy human subjects. Although it is without doubt that protein fermentation yields intrinsically toxic luminal compounds that affect epithelial cell metabolism and barrier function, we hypothize that the impact of protein fermentation is overshadowed by other dietary or lifestyle factors.status: publishe

Contribution of Colonic Fermentation and Fecal Water Toxicity to the Pathophysiology of Lactose-Intolerance

Whether or not abdominal symptoms occur in subjects with small intestinal lactose malabsorption might depend on differences in colonic fermentation. To evaluate this hypothesis, we collected fecal samples from subjects with lactose malabsorption with abdominal complaints (LM-IT, n = 11) and without abdominal complaints (LM-T, n = 8) and subjects with normal lactose digestion (NLD, n = 15). Lactose malabsorption was diagnosed using a (13)C-lactose breath test. Colonic fermentation was characterized in fecal samples at baseline and after incubation with lactose for 3 h, 6 h and 24 h through a metabolomics approach using gas chromatography-mass spectrometry (GC-MS). Fecal water cytotoxicity was analyzed using a colorimetric assay. Fecal water cytotoxicity was not different between the three groups (Kruskall-Wallis p = 0.164). Cluster analysis of the metabolite patterns revealed separate clusters for NLD, LM-T and LM-IT samples at baseline and after 24 h incubation with lactose. Levels of 5-methyl-2-furancarboxaldehyde were significantly higher in LM-IT and LM-T compared to NLD whereas those of an unidentified aldehyde were significantly higher in LM-IT compared to LM-T and NLD. Incubation with lactose increased short chain fatty acid (SCFA) concentrations more in LM-IT and LM-T compared to NLD. In conclusion, fermentation patterns were clearly different in NLD, LM-IT and LM-T, but not related to differences in fecal water cytotoxicity.status: publishe

Tolerance and the effect of high doses of wheat bran extract, containing arabinoxylan-oligosaccharides, and oligofructose on faecal output: a double- blind, randomised, placebo-controlled, cross-over trial

Wheat bran extract (WBE) is a food-grade soluble fibre preparation that is highly enriched in arabinoxylan-oligosaccharides. In this placebo-controlled cross-over human intervention trial, tolerance to WBE as well as the effects of WBE on faecal parameters, including faecal output and bowel habits, were studied. After a 2-week run-in period, twenty healthy volunteers consumed WBE (15 g/d in the first week, 30 g/d in the second week), oligofructose (15 g/d in the first week, 30 g/d in the second week) and placebo (for 2 weeks) in a random order, with 2-week washout periods between each treatment period. Subjects collected a 72 h stool sample for analysis of faecal output, stool pH and stool moisture concentration. Additionally, the volunteers completed questionnaires scoring occurrence frequency and distress severity of eighteen gastrointestinal (GI) symptoms. An overall GI symptom measure was calculated to analyse the overall effect of WBE and oligofructose on GI symptoms. Intake of both 30 g/d WBE and 30 g/d oligofructose lowered stool pH, indicative of increased colonic fermentation, and increased stool moisture concentration as compared with placebo intake. Intake of 30 g/d oligofructose increased the overall GI symptom measure by 1·9-fold as compared with placebo intake. Intake of WBE at doses up to 30 g/d did not affect the overall GI symptom measure. WBE exerts beneficial effects on stool characteristics and is well tolerated at up to 30 g/d. Oligofructose exerts comparable beneficial effects on stool characteristics. However, intake of 30 g/d oligofructose appears to cause GI discomfort to some extent.status: publishe