Lieselotte Cloetens

Tolerance of arabinoxylan-oligosaccharides and their prebiotic activity in healthy subjects: a randomised, placebo-controlled cross-over study.

The tolerance and prebiotic effect following oral intake by healthy human subjects of arabinoxylan-oligosaccharides (AXOS), produced by partial enzymic hydrolysis of the wheat fibre arabinoxlyan, were studied. A total of twenty healthy subjects participated in the present randomised, placebo-controlled cross-over study. They consumed 10 g AXOS or placebo per d each for 3 weeks with a 4-week wash-out period in between. Before and immediately after each intake period, blood samples were taken to measure haematological and clinical chemistry parameters and the subjects completed a questionnaire about gastrointestinal symptoms. Additionally, urine was collected over 48 h for analysis of p-cresol and phenol content by GC-MS, and faeces were collected over 72 h for analysis of microbiota using real-time PCR. Of the subjects, ten also performed a urine and faeces collection 2 weeks after the start of intake (during intervention). A limited number of tested blood parameters were influenced in a statistically significantly way by either AXOS or placebo intake, but these changes remained within the normal range. Blood lipids remained unchanged. AXOS had no statistically significant effect on the range of gastrointestinal symptoms, except for a mild increase in flatulence. Urinary p-cresol excretion, an indicator of protein fermentation, was significantly decreased after 2 weeks of AXOS intake. The levels of bifidobacteria were significantly increased after 2 and 3 weeks of AXOS intake as well as after 3 weeks of placebo. However, the effect of AXOS on bifidobacteria was more pronounced than that of placebo. In conclusion, AXOS are a well-tolerated prebiotic at the dose of 10 g/d. AXOS intake increases faecal bifidobacteria and reduces urinary p-cresol excretion.

Dose-Response Effect of Arabinoxylooligosaccharides on Gastrointestinal Motility and on Colonic Bacterial Metabolism in Healthy Volunteers

Objective: Arabinoxylooligosaccharides (AXOS) are non-digestible in the upper gastrointestinal tract and have been shown to exert prebiotic effects in animals. The aim of this study was to characterize the influence of AXOS with an average degree of polymerization of 15 and an average degree of arabinose substitution of 0.26 (AXOS-15-0.26) on gastrointestinal motility and colonic bacterial metabolism in healthy human volunteers. Methods: Twelve healthy volunteers received five test meals, containing different amounts of AXOS-15-0.26, with one week intervals between each test meal. Breath tests were used to measure gastric emptying rate, oro-cecal transit time (OCTT) and hydrogen excretion. Colonic bacterial metabolism was estimated using the biomarkers lactose-[15N, 15N′]-ureide (15N-LU) and p-cresol. Results: Gastric emptying and OCTT were not influenced by addition of varying amounts of AXOS-15-0.26. Administration of 2.2g or 4.9g AXOS-15-0.26 significantly decreased the urinary 15N-excretion (respectively p = 0.008 and p = 0.035) as compared to the baseline, whereas fecal 15N-excretion was significantly increased (respectively p = 0.034 and p = 0.019). This shift from urinary to fecal 15N-excretion suggests a higher uptake or incorporation by bacteria due to the stimulation of colonic bacterial growth and/or metabolic activity. Furthermore, a significant increase in hydrogen excretion after administration of 2.2g (p = 0.002) and 4.9g (p = 0.004) AXOS-15-0.26 was observed. No influence on urinary p-cresol excretion was observed. Conclusion: These findings suggest that a minimal dose of 2.2g AXOS-15-0.26 favorably modulates the colonic bacterial metabolism in healthy humans. However, long term studies are required to confirm a possible prebiotic effect.

Consumption of Breads Containing In Situ–Produced Arabinoxylan Oligosaccharides Alters Gastrointestinal Effects in Healthy Volunteers

Arabinoxylan oligosaccharides (AXOS) are studied as food compounds with prebiotic potential. Here, the impact of consumption of breads with in situ-produced AXOS on intestinal fermentation and overall gastrointestinal characteristics was evaluated in a completely randomized, double-blind, controlled, cross-over study. Twenty-seven healthy volunteers consumed 180 g of wheat/rye bread with or without in situ-produced AXOS (WR(+) and WR(-), respectively) daily for 3 wk. Consumption of WR(+) corresponded to an AXOS intake of ~2.14 g/d. Refined wheat flour bread without AXOS (W(-)) (180 g/d) was provided during the 3-wk run-in and wash-out periods. At the end of each treatment period, participants collected urine for 48 h as well as a feces sample. Additionally, all participants completed a questionnaire about stool characteristics and gastrointestinal symptoms during the last week of each period. Urinary phenol and p-cresol excretions were significantly lower after WR(+) intake compared to WR(-). Consumption of WR(+) significantly increased fecal total SCFA concentrations compared to intake of W(-). The effect of WR(+) intake was most pronounced on butyrate, with levels 70% higher than after consumption of W(-) in the run-in or wash-out period. Consumption of WR(+) tended to selectively increase the fecal levels of bifidobacteria (P = 0.06) relative to consumption of W(-). Stool frequency increased significantly after intake of WR(+) compared to WR(-). In conclusion, consumption of breads with in situ-produced AXOS may favorably modulate intestinal fermentation and overall gastrointestinal properties in healthy humans.

Influence of resistant starch alone or combined with wheat bran on gastric emptying and protein digestion in healthy volunteers

Objective. Resistant starch (RS) is not absorbed in the small intestine, but is partly fermented in the colon and may positively influence putative risk factors for colon cancer. The purpose of the study was to investigate the influence of RS type 3 (retrograded amylose) alone or combined with wheat bran on gastric emptying (GE) and protein assimilation. Material andmethods. GE and protein assimilation were investigated by means of breath-test technology in 20 healthy volunteers who were randomly divided into two groups, each subject performing two tests. In each test, the volunteers received a labelled test meal either as such or in combination with, respectively, 15 g RS3 or 15 g RS3 combined with 6 g wheat bran (WB). Breath samples were collected during the 6 h after administration of a test meal containing egg proteins, intrinsically labelled with 13C-leucine, to measure protein digestion and sodium-14C-octanoate for measurement of GE. Results. Intake of RS3 +WB did not influence GE time compared to baseline values, whereas intake of RS3 seemed to hasten GE: from 93±32 min to 55±15 min (p=0.012). The overall protein assimilation parameters at baseline were not significantly different from those obtained after simultaneous intake of RS3 +WB, whereas RS3 significantly shortened the time of maximum excretion compared to baseline, but the extent of protein digestion after RS3 intake was not affected (12.54±3.60% versus 13.43±3.40%). Conclusions. The presence of RS3 alone or in combination with wheat bran demonstrates that there are no adverse effects on protein digestion and no influence on the nitrogen supply to the colon.

W1383 The Effect of Two Different Doses of Arabinoxylo-Oligosaccharides and Oligofructose Enriched Inulin On the Colonic Ammonia Metabolism in Healthy Volunteers

Introduction: Previous studies using the biomarker lactose-[15N,15N]-ureide (15N-LU), a precursor molecule that introduces a known amount of NH3 in the colon, have shown that prebiotics beneficially influence the colonic ammonia metabolism. They increase the faecal 15N-excretion while reducing the urinary 15N-excretion, which indicates a lower colonic generation of ammonia and/or a higher bacterial uptake due to stimulation of bacterial growth and/or activity. In this study, the influence of arabino-oligosaccharides (AXOS, degree of polymerisation = 9, degree of arabinose substitution = 0.25) on the colonic ammonia metabolism was compared to that of oligofructose-enriched inulin (OF-IN). Materials and methods: Two cross-over studies with different doses of AXOS and OF-IN were performed. In the first study, 13 healthy volunteers were administered 5.0g/day AXOS or OF-IN during two weeks with a 3-weeks wash-out period in between. In the second study, 11 healthy volunteers were administered 2.25g/day AXOS and OF-IN. Before, at the start (short term) and immediately after (long term) each intake period, a test meal labelled with 15N-LU and 3H-PEG, as an inert marker to measure total gastrointestinal transit, was consumed. After each test meal, a fractionated urine collection (48h) and faeces collection (72h) were performed. 15N-enrichment in urine and faeces was measured by combustion-IRMS. Results are expressed as % of the administered dose. Urinary data were corrected for creatinine content. Faecal data were corrected for total transit. Results: After short term intake of 5.0g/ day AXOS or OF-IN, urinary 15N-excretion was significantly decreased (p= 0.01 and p= 0.03, respectively) as compared to baseline, whereas a significant increase in faecal 15Nexcretion was observed after intake of AXOS (p<0.01) and OF-IN (p<0.01). After long term intake of AXOS, there was a significant decrease in urinary 15N-excretion (p=0.03). However, urinary 15N-excretion after long term intake of OF-IN was not influenced. Faecal 15Nexcretion trended to an increase after long term intake of AXOS but remained unchanged after OF-IN treatment. On the other hand, the intake of 2.25g AXOS and OF-IN did not influence urinary and faecal 15N-excretion after short term intake as well as long term intake. Conclusion: At a dose of 5.0g/day, AXOS beneficially influence the colonic ammonia metabolism in a similar way of OF-IN.

T2026 A Dietary Intervention With Arabinoxylan Oligosaccharides Reduces Colonic Protein Fermentation in Healthy Subjects: Results From Faecal Metabolite Fingerprint Analysis

Background The addition of prebiotics to the diet may improve host health by modulation of the colonicmetabolism. The effect of a new candidate prebiotic, arabinoxylan oligosaccharides (AXOS), on the colonic metabolism was evaluated by characterization of the metabolite profile in faeces. Methods AXOS was administered for 3 weeks at 10 g/day to 20 healthy volunteers (30% male; age 23(20-45); BMI 21(18-26)). Faecal samples were collected before and after the intervention with AXOS. To determine a broad range of fermentation metabolites, metabolic fingerprinting was applied using a purge-and-trap system coupled on-line to a gas chromatograph time-of-flight mass spectrometer (GC-TOF-MS). Cluster analysis, based on relative indices of all identified volatile organic compounds (VOCs) versus 2ethylbutyric acid as internal standard, was used to compare the metabolite profiles. Results A total of 179 different VOCs were identified in the faecal samples, 24 VOCs were present in more than 70% of the samples. The compounds acetaldehyde, butanoic acid, dimethyl disulfide, dimethyl trisulphide and limonene were present in all samples. Cluster analysis of the VOC fingerprints allowed to discriminate baseline samples from the samples after the intervention with AXOS, suggesting that the impact of the intervention exceeded the interindividual variability (Figure). This discrimination was mainly due to protein fermentation metabolites such as p-cresol, branched-chain fatty acids (4-methyl pentanoic acid, 2-methyl propanoic acid and 3methyl butanoic acid) and sulphur containing compounds (hydrogen sulphide, carbon disulfide, dimethyl tetrasulfide). Faecal short-chain fatty acids did not contribute to discrimination between both groups, although this does not preclude an increased SCFA production in the proximal colon. Conclusion Dietary intervention with AXOS has a considerable impact on the colonic metabolism mainly by decreasing proteolytic activity.