Alternative pathways for hydrogen disposal during fermentation in the human colon

Modeling 13C breath curves to determine site and extent of starch digestion and fermentation in infants

BACKGROUND

The colon salvages energy from starch, especially when the capacity of the small intestine to digest it is limited. The aim of this study was to determine the site and relative extent of starch digestion and fermentation in infants.

METHODS

Thirteen infants (10 male and 3 female infants), median age 11.8 months (range, 7.6-22.7 months), were fed a starchy breakfast containing 13C-labeled wheat flour after an overnight fast. Duplicate breath samples were obtained before breakfast and every 30 minutes for 12 hours. Breath 13CO2 enrichment was measured using isotope ratio mass spectrometry, and results were expressed as percentage dose recovered (PDR) for each 30 minutes. The PDR data were analyzed and mathematically modeled assuming either a constant estimate of CO2 production rate or adjusted for physical activity.

RESULTS

Mean +/- SD cumulative 13C PDR (cPDR) at 12 hours was 21.3% +/- 8.4% for unadjusted data and 26.5% +/- 11.6% for adjusted data. A composite model of two curves fit significantly better than a single curve. Modeling allowed estimation of cPDRs of small intestine (17.5% +/- 6.5% and 22.7% +/- 9.3% for unadjusted and adjusted data, respectively) and colon (4.6% +/- 2.9% and 6.3% +/- 5.4%).

CONCLUSIONS

Modeling of 13CO2 enrichment curves after ingestion of 13C-enriched wheat flour is an attractive means to estimate the contribution of the upper and lower gut to starch digestion and fermentation.

Nutritional supplements used in weight-reduction programs increase intestinal gas in persons who malabsorb lactose

OBJECTIVE

To determine if ingestion of 2 doses of milk-based dietary supplements produce gaseous symptoms in subjects who malabsorb lactose.

DESIGN

Randomized, controlled, crossover trial.

SUBJECTS/SETTING

Ten community-based subjects who malabsorb lactose.

INTERVENTION

Ingestion of 2 standard servings of milk-based supplements (a powder reconstituted in fat-free milk or a ready-to-drink preparation) or low-lactose control preparations.

MAIN OUTCOME MEASURES

Frequency of flatus passage and subjective impression of bloating, flatulence, and abdominal discomfort.

STATISTICAL ANALYSIS

Wilcoxon signed-rank test.

RESULTS

The high lactose content (27 g) of 2 servings of the powder-based supplement ingested without other food resulted in a marked increase in daily flatus passages from the basal level of 9.7+/-8.2 to 30+/-14 (mean+/-SD), and a significant increase in the subjects' perception of gas. In contrast, the lower lactose content (18.4 g) of 2 servings of a ready-to-drink supplement resulted in a flatus frequency of 17+/-10 (P=.14 vs baseline) and no significant increase in the perception of increased gas. Neither supplement resulted in a significant increase in bloating, abdominal pain, or diarrhea. The lactose content of the liquid supplement was reduced by 80% following overnight incubation with an over-the-counter lactase preparation.

APPLICATIONS/CONCLUSIONS

Persons who malabsorb lactose should be aware that sizable increases in rectal gas commonly occur when milk-based powders reconstituted in milk are used as meal replacements. In contrast, gas problems probably will be minor following ingestion of 2 doses of a ready-to-drink, milk-based supplement. The lactose content of these supplements can be markedly reduced by overnight incubation with over-the-counter lactase preparations, and this manipulation should be beneficial for subjects troubled by the increased gas caused by the consumption of lactose-containing supplements.

Hydrogen sulfide and colonic epithelial metabolism: implications for ulcerative colitis

Hydrogen sulfide (HS-) impairs the oxidation of butyrate in colonocytes and is found in excess in feces of patients with ulcerative colitis. The possible pathogenic role of HS- in ulcerative colitis was further investigated. To investigate the metabolic effect of free and bound fecal HS-, isolated rat colonocytes were incubated in the presence of butyrate without and with the addition of (1) HS- in water, (2) sterile filtrates of fecal homogenates supplemented and incubated with HS- and known sources of fecal HS- production, and (3) HS- incubated with fecal agents known to bind HS-. Oxidation rates were obtained by quantifying the production of CO2. Total and free HS-, as well as the fecal ability to bind HS-, were determined in health and ulcerative colitis. Compared to the production of CO2 by colonocytes incubated with 2 mmol/liter of butyrate, the further addition of 1.25 and 2.5 mmol/liter of HS- in water reduced the production of CO2 by 57.6+/-10.0 and 98.9+/-1.4%, respectively. However, when adding fecal filtrate of homogenate supplemented with HS- corresponding to 1.25 and 2.5 mmol/liter of HS- in water, the reduction of CO2 production was only 30.7+/-12.0 and 53.2+/-14.0%, respectively. Neither the fecal level of total or free HS- nor the remarkable fecal ability to bind HS- differed in health or quiescent and active ulcerative colitis. Bound HS- had no or little effect on CO2 production. Addition of fecal filtrate of nonsupplemented homogenate to colonocytes significantly reduced the oxidation of butyrate to CO2 about 25%, which could not be ascribed to fecal HS-. In conclusion, fecal HS- has little effect on butyrate oxidation in colonocytes and does not seem to play a pathogenic role for UC by impairing colonic epithelial metabolism. Other fecal agents seem to be more potent metabolic inhibitors than fecal HS-. The role of colonic contents in the pathogenesis of ulcerative colitis remains circumstantial.

Measurement of fecal sulfide using gas chromatography and a sulfur chemiluminescence detector

We describe a simple technique to measure sulfide in fecal homogenates (or any other liquid milieu), which involves acidification followed by the G.C. measurement of H2S in a gas space equilibrated with a small quantity of homogenate. An internal standard of Zn35S added to the homogenate permits correction for incomplete recovery of H2S in the gas space. The use of a sulfur chemiluminescence detector, which specifically and sensitively responds to sulfur-containing compounds, greatly facilitates this measurement.

Screening of sulfate-reducing bacteria in colonoscopy samples from healthy and colitic human gut mucosa

A PCR-based approach combined with microbiological cultivation methods was employed to determine the occurrence of sulfate-reducing bacteria (SRB) in colon biopsy samples from ulcerative colitis patients and from non-colitic controls. The detection of mucosa-associated SRB was carried out by digoxigenin-dUTP-labelled PCR amplification, in liquid Postgate medium B and in a new liquid medium, termed VM medium I. Using Postgate medium B, the growth of SRB was confirmed in 92% of the colitic specimens and in 52% of non-colitic samples. However, PCR analysis and incubation in VM medium I detected SRB in 100% of biopsy material indicating ubiquitous presence of SRB in human colon mucosa.

Contribution of dietary protein to sulfide production in the large intestine: an in vitro and a controlled feeding study in humans

BACKGROUND

Hydrogen sulfide is a luminally acting, bacterially derived cell poison that has been implicated in ulcerative colitis. Sulfide generation in the colon is probably driven by dietary components such as sulfur-containing amino acids (SAAs) and inorganic sulfur (eg, sulfite).

OBJECTIVE

We assessed the contribution of SAAs from meat to sulfide production by intestinal bacteria with use of both a model culture system in vitro and an in vivo human feeding study.

DESIGN

Five healthy men were housed in a metabolic suite and fed a sequence of 5 diets for 10 d each. Meat intake ranged from 0 g/d with a vegetarian diet to 600 g/d with a high-meat diet. Fecal sulfide and urinary sulfate were measured in samples collected on days 9 and 10 of each diet period. Additionally, 5 or 10 g bovine serum albumin or casein/L was added to batch cultures inoculated with feces from 4 healthy volunteers. Concentrations of sulfide, ammonia, and Lowry-reactive substances were measured over 48 h.

RESULTS

Mean (+/-SEM) fecal sulfide concentrations ranged from 0.22 +/- 0.02 mmol/kg with the 0-g/d diet to 3.38 +/- 0.31 mmol/kg with the 600-g/d diet and were significantly related to meat intake (P: < 0.001). Sulfide formation in fecal batch cultures supplemented with both bovine serum albumin and casein correlated with protein digestion, as measured by the disappearance of Lowry-reactive substances and the appearance of ammonia.

CONCLUSION

Dietary protein from meat is an important substrate for sulfide generation by bacteria in the human large intestine.

The contribution of sulphate reducing bacteria and 5-aminosalicylic acid to faecal sulphide in patients with ulcerative colitis

BACKGROUND

Butyrate oxidation within the colonocyte is selectively inhibited by hydrogen sulphide, reproducing the metabolic lesion observed in active ulcerative colitis.

AIMS

To study generation of hydrogen sulphide by sulphate reducing bacteria (SRB) and the effects of 5-aminosalicylic acid (5-ASA) in patients with ulcerative colitis in order to identify a role of this noxious agent in pathogenesis.

PATIENTS

Fresh faeces were obtained from 37 patients with ulcerative colitis (23 with active disease) and 16 healthy controls.

METHODS

SRB were enumerated from fresh faecal slurries and measurements made of sulphate reducing activity, and sulphate and hydrogen sulphide concentrations. The effect of 5-ASA on hydrogen sulphide production was studied in vitro.

RESULTS

All controls and patients with active ulcerative colitis carried SRB and total viable counts were significantly related to the clinical severity grade. SRB were of two distinct types: rapidly growing strains (desulfovibrios) which showed high sulphate reduction rates, present in 30% of patients with ulcerative colitis and 44% of controls; and slow growing strains which had little activity. In vitro, 5-ASA inhibited sulphide production in a dose dependent manner; in patients with ulcerative colitis not on these drugs faecal sulphide was significantly higher than in controls (0.55 versus 0.25 mM, p=0.027).

CONCLUSIONS

Counts and carriage rates of SRB in faeces of patients with ulcerative colitis are not significantly different from those in controls. SRB metabolism is not uniform between strains and alternative sources of hydrogen sulphide production exist in the colonic lumen which may be similarly inhibited by 5-ASA. The evidence for hydrogen sulphide as a metabolic toxin in ulcerative colitis remains circumstantial.

Importance of colonic bacterial fermentation in short bowel patients: small intestinal malabsorption of easily digestible carbohydrate

The small intestine's large capacity for glucose absorption and for adaptation seems to contradict the reported importance of carbohydrate malabsorption in short bowel (SB) patients. The aim of the present study was to investigate the occurrence of malabsorption in these patients ingesting realistic amounts of carbohydrates. We performed a dose-response study [ingestion of increasing amounts of glucose and complex carbohydrates (boiled rice and wheat bread), and the nonabsorbable disaccharide lactulose] in SB patients with an intact colon. The hydrogen (H2) -breath test and changes in serum acetate were used to evaluate colonic fermentation and, thus, indirectly, the lack of small intestinal carbohydrate assimilation. Blood glucose and plasma insulin were measured to evaluate absorption. Plasma concentrations of the ileal brake hormones--glucagon-like peptide-1 (GLP-1) and peptide tyrosine tyrosine (PYY)--were measured to test whether release of these hormones was related to colonic fermentation. Significant amounts of 25 g and 50 g glucose, and of the bread and rice meals were fermented rather than absorbed, as judged by the increases in end-expiratory H2. Serum acetate concentrations were significantly higher in SB patients than in healthy controls. The orocecal transit times of all test meals ranged from 15 to 120 min. GLP-1 and PYY releases in SB patients were significantly higher than in healthy volunteers. They were mutually parallel and paralleled the increase in insulin. They were not related to ongoing fermentation or to intraluminal carbohydrate content per se, but most probably to absorption of glucose in the distal bowel. In conclusion, well-adapted SB patients had pronounced small intestinal malabsorption of carbohydrate, even after ingestion of small amounts of easily absorbable carbohydrates. A fast small intestinal spreading of carbohydrates, once in the small intestine, and a spill-over to the colon seem to explain the data best.

Low trehalase activity is associated with abdominal symptoms caused by edible mushrooms

BACKGROUND

The purpose of the study was to evaluate whether maldigestion of trehalose causes abdominal symptoms and which available diagnostic method best distinguishes intolerant from tolerant subjects.

METHODS

A 25-g oral trehalose load test was performed in 64 subjects. The 19 experiencing clear symptoms constituted the trehalose-intolerant subjects. Changes from base-line levels of blood glucose, breath hydrogen, and methane and symptoms were recorded after the test. Trehalase activity was determined in serum and on a duodenal biopsy specimen obtained by endoscopy.

RESULTS

Intolerant subjects were best differentiated from tolerant subjects by changes in breath gases (hydrogen and methane) and duodenal trehalase to sucrase ratio. The change in breath gases correlated inversely with duodenal trehalase activity, duodenal trehalase to sucrase ratio, and plasma trehalase activity. The correlation between serum and duodenal trehalase activities was on the order of 0.6. Two subjects were found to have trehalase deficiency.

CONCLUSIONS

It is obvious that trehalose maldigestion can cause symptoms similar to those of lactose maldigestion and intolerance. Three factors control the genesis of symptoms: 1) the activity of small-bowel trehalase: if it is low, trehalose is maldigested and more trehalose is passed into the colon; 2) the maldigested trehalose, which causes osmotic water flow into the colon, resulting in loose stools and diarrhea; and 3) most importantly, the microflora of the colon, from which symptoms will arise if there are bacteria capable of producing gases from maldigested trehalose. If colonic bacteria cannot produce gases, then distention of the abdomen and intestinal gas expulsion as eructations and flatus will not occur.

Breath hydrogen and methane responses of men and women to breads made with white flour or whole wheat flours of different particle sizes

OBJECTIVE

While it is well known that consumption of whole grain foods results in beneficial health effects, the great majority of Americans prefer bread made with white flour. Consumption of whole grain foods in high fiber menus may cause undesirable intestinal responses. The purpose of this study was to determine whether consumption of bread made with ultra fine ground whole wheat flour retained beneficial effects while reducing undesirable effects.

METHODS

Twenty-six men and women (31 to 55 years of age) consumed glucose solutions or bread made with white, whole wheat or fine ground whole wheat flour (1 g carbohydrate/kg body weight) in a Latin square design after two days of controlled diet. Breath methane and hydrogen were determined over the 24 hours after consumption of test foods.

RESULTS

Hydrogen and methane responses of men and women were similar. There were no significant differences in methane responses to the different treatments, but hydrogen response was increased by all breads (p<0.0001). Although the overall mean response values were similar for all three breads, the patterns of hydrogen response differed (treatment*time, p<0.003). Gastrointestinal symptoms were not associated with fiber content or particle size of bread; however, subjects reporting symptoms tended to have higher methane responses (0.05<p<0.10).

CONCLUSION

Neither fiber content of bread nor particle size of whole wheat flour substantially affected breath hydrogen or methane responses or gastrointestinal symptoms. Fine ground whole wheat breads may provide a more acceptable food choice than standard whole wheat bread without sacrificing the beneficial health effects of higher fiber.

Gas production in human ingesting a soybean flour derived from beans naturally low in oligosaccharides

BACKGROUND

Ingestion of soy products may cause excessive intestinal gas. This gas results from colonic bacterial fermentation of the indigestible oligosaccharides raffinose and stachyose, which are present in high concentrations in legumes.

OBJECTIVE

The objective of the study was to compare gas production and gaseous symptoms in healthy volunteers after ingestion of 34 and 80 g soy flour made from either conventional soybeans or soybeans naturally low in indigestible oligosaccharides.

DESIGN

In a double-blind, randomized, crossover protocol, breath hydrogen (an indicator of carbohydrate malabsorption), flatus frequency, and abdominal symptoms were assessed after subjects ingested the soy products and after 2 control meals (rice or lactose-hydrolyzed milk).

RESULTS

The sum of breath-hydrogen concentrations for 8 h was significantly greater (P < 0.005) after 34 g conventional soy (60.4+/-9.4 ppm) than after low-oligosaccharide soy (34.3+/-8.1 ppm). Greater differences were observed with 80-g doses: 157.9+/-19.4 ppm after conventional soy and 50.8+/-6.8 ppm after low-oligosaccharide soy (P < 0.001). Flatus frequency (7.5+/-1.9 times/12 h) was significantly greater (P = 0.039) after ingestion of 80 g conventional soy than after the control, rice meal (3.2+/-0.8 times/12 h), whereas flatus frequency after the low-oligosaccharide soy meal (3.9+/-0.7 times/12 h) was comparable with that after the rice meal. There were no significant differences in the severity of other abdominal symptoms.

CONCLUSION

Soy flour derived from low-oligosaccharide soybeans resulted in less gas production than that derived from conventional soybeans.

Evaluation of an extremely flatulent patient: case report and proposed diagnostic and therapeutic approach

We recently encountered a patient with severe flatulence who previously had been subjected to innumerable diagnostic tests and ineffective therapies based on the belief that his rectal gas was produced in the colon. Analysis of three flatus samples demonstrated that nitrogen (N2) was the predominant flatus gas whereas the three gases produced in the gut (CO2, H2 [hydrogen], and CH4 [methane]) comprised <16% of rectal gas. This result plus a series of other diagnostic tests clearly indicated that the patient's flatus was derived almost entirely from swallowed air. Based on this case, the present report summarizes available data on excessive flatulence and suggests a rational approach to the patient complaining of this problem. Particular emphasis is placed upon a sequential strategy consisting of: 1) a count of flatus passages to determine if the subject truly is abnormal (normal: <20 passages/day); 2) an analysis of flatus to determine if the flatus originates from swallowed air (predominantly nitrogen) or intraluminal production (predominantly CO2, H2, and CH4); and 3) treatment based upon the origin of the rectal gas.

Consumption of exogenous bifidobacteria does not alter fecal bifidobacteria and breath hydrogen excretion in humans

The hypothesis that consumption of bifidobacteria by humans would increase colonic bifidobacteria and decrease breath hydrogen excretion was examined. A commercially available strain of bifidobacteria was tracked through the gastrointestinal tract. We determined that a 12-d feeding period of 10(10) cells of exogenous bifidobacteria daily was adequate to achieve a stable number of exogenous bifidobacteria in the colon. A 12-d washout period was chosen because the exogenous bifidobacteria could no longer be detected at that time. A double-blind crossover study used both male and female subjects. The order of treatment with skim milk alone or skim milk + bifidobacteria was randomized. Breath hydrogen excretion (micromol/L) and fecal counts of total bifidobacteria [log colony forming units (CFU)/g feces] were not significantly different between males and females and were not affected by consumption of exogenous bifidobacteria. Calculations based on the numbers of exogenous bifidobacteria consumed and the fecal numbers of exogenous bifidobacteria excreted suggested that numbers of the exogenous strain increased within the gastrointestinal tract. These data suggest that it is difficult to permanently alter total colonic bifidobacteria and affect physiologic function (net hydrogen in the colon as reflected by breath hydrogen) by feeding bifidobacteria, although the percentage of the total bifidobacteria represented by the exogenous strain can be affected.

Contributions of microbes in vertebrate gastrointestinal tract to production and conservation of nutrients

The vertebrate gastrointestinal tract is populated by bacteria and, in some species, protozoa and fungi that can convert dietary and endogenous substrates into absorbable nutrients. Because of a neutral pH and longer digesta retention time, the largest bacterial populations are found in the hindgut or large intestine of mammals, birds, reptiles, and adult amphibians and in the foregut of a few mammals and at least one species of bird. Bacteria ferment carbohydrates into short-chain fatty acids (SCFA), convert dietary and endogenous nitrogenous compounds into ammonia and microbial protein, and synthesize B vitamins. Absorption of SCFA provides energy for the gut epithelial cells and plays an important role in the absorption of Na and water. Ammonia absorption aids in the conservation of nitrogen and water. A larger gut capacity and longer digesta retention time provide herbivores with additional SCFA for maintenance energy and foregut-fermenting and copoprophagic hindgut-fermenting species with access to microbially synthesized protein and B vitamins. Protozoa and fungi also contribute nutrients to the host. This review discusses the contributions of gut microorganisms common to all vertebrates, the numerous digestive strategies that allow herbivores to maximize these contributions, and the effects of low-fiber diets and discontinuous feeding schedules on these microbial digestive processes.

Fecal hydrogen sulfide production in ulcerative colitis

OBJECTIVE

Sulfide, a product of sulfate-reducing bacteria, has been proposed to play an etiologic role in ulcerative colitis. Ulcerative colitis feces have increased numbers and activity of sulfate-reducing bacteria, but only modestly increased sulfide. However, fecal sulfide exists largely in the volatile, highly toxic H2S form that moves rapidly from feces to surrounding gas. Our aim was to quantify the fecal release of H2S and other volatiles (CO2, H2, CH4, methanethiol, and dimethylsulfide).

METHODS

Fecal samples from 25 subjects with ulcerative colitis and 17 controls were incubated in 4-L containers, and gas release was assessed at intervals over 24 h.

RESULTS

H2S release by ulcerative colitis feces was elevated 3-4-fold at every measurement point compared with normal feces (p < 0.003 at 24 h). The only other significant difference was increased CO2 release by ulcerative colitis feces at 1 h. Supplementation of fecal homogenates with sulfur-containing substrates showed that organic compounds (mucin, cysteine, taurocholate) provided more readily utilizable substrate for H2S production than did sulfate.

CONCLUSIONS

Increased H2S release is a relatively localized metabolic aberration of ulcerative colitis feces. This increased H2S may reflect abnormalities of the fecal bacteria and/or substrate availability.

Colonic sulfide in pathogenesis and treatment of ulcerative colitis

A role for colonic sulfide in the pathogenesis and treatment of ulcerative colitis (UC) has emerged based on biochemical, microbiological, nutritional, toxicological, epidemiological, and therapeutic evidence. Metabolism of isolated colonic epithelial cells has indicated that the bacterial short-chain fatty acid n-butyrate maintains the epithelial barrier and that sulfides can inhibit oxidation of n-butyrate analogous to that observed in active UC. Sulfur for fermentation in the colon is essential for n-butyrate formation and sulfidogenesis aids disposal of colonic hydrogen produced by bacteria. The numbers of sulfate-reducing bacteria and sulfidogenesis is greater in UC than control cases. Sulfide is mainly detoxified by methylation in colonic epithelial cells and circulating red blood cells. The enzyme activity of sulfide methylation is higher in red blood cells of UC patients than control cases. Patients with UC ingest more protein and thereby sulfur amino acids than control subjects. Removing foods rich in sulfur amino acids (milk, eggs, cheese) has proven therapeutic benefits in UC. 5-Amino salicylic acid reduces fermentative production of hydrogen sulfide by colonic bacteria, and aminoglycosides, which inhibit sulfate-reducing bacteria, are of therapeutic benefit in active UC. Methyl-donating agents are a category of drugs of potential therapeutic use in UC. A correlation between sulfide production and mucosal immune responses in UC needs to be undertaken. Control of sulfidogenesis and sulfide detoxification may be important in the disease process of UC, although whether their roles is in an initiating or promoting capacity has yet to be determined.

Colonic sulfide in pathogenesis and treatment of ulcerative colitis

A role for colonic sulfide in the pathogenesis and treatment of ulcerative colitis (UC) has emerged based on biochemical, microbiological, nutritional, toxicological, epidemiological, and therapeutic evidence. Metabolism of isolated colonic epithelial cells has indicated that the bacterial short-chain fatty acid n-butyrate maintains the epithelial barrier and that sulfides can inhibit oxidation of n-butyrate analogous to that observed in active UC. Sulfur for fermentation in the colon is essential for n-butyrate formation and sulfidogenesis aids disposal of colonic hydrogen produced by bacteria. The numbers of sulfate-reducing bacteria and sulfidogenesis is greater in UC than control cases. Sulfide is mainly detoxified by methylation in colonic epithelial cells and circulating red blood cells. The enzyme activity of sulfide methylation is higher in red blood cells of UC patients than control cases. Patients with UC ingest more protein and thereby sulfur amino acids than control subjects. Removing foods rich in sulfur amino acids (milk, eggs, cheese) has proven therapeutic benefits in UC. 5-Amino salicylic acid reduces fermentative production of hydrogen sulfide by colonic bacteria, and aminoglycosides, which inhibit sulfate-reducing bacteria, are of therapeutic benefit in active UC. Methyl-donating agents are a category of drugs of potential therapeutic use in UC. A correlation between sulfide production and mucosal immune responses in UC needs to be undertaken. Control of sulfidogenesis and sulfide detoxification may be important in the disease process of UC, although whether their roles is in an initiating or promoting capacity has yet to be determined.

Fecal hydrogen production and consumption measurements. Response to daily lactose ingestion by lactose maldigesters

The alteration of hydrogen (H2) metabolism, which accounts for the large decrease in breath H2 excretion following prolonged ingestion of malabsorbed carbohydrate (lactulose, lactose in lactose maldigesters) was studied in six lactose-maldigesting adults. Metabolic inhibitors of the three main H2-consuming reactions (methanogenesis, sulfate reduction, and acetogenesis) were used to independently measure H2 production and consumption in fecal samples obtained after 10 days of either dextrose or lactose feeding. Absolute fecal H2 production (net of production minus consumption) after 3 hr of incubation with lactose was approximately threefold lower after lactose adaptation (242 +/- 54 microliters) compared to dextrose adaptation (680 +/- 79 microliters, P = 0.006). Fecal H2 consumption was not affected by either feeding period. We conclude that decreased absolute H2 production, rather than increased H2 consumption, is responsible for the decrease in breath H2 observed with lactose feeding.

Effect of 2-bromoethanesulfonic acid and Peptostreptococcus productus ATCC 35244 addition on stimulation of reductive acetogenesis in the ruminal ecosystem by selective inhibition of methanogenesis

Evidence is provided that reductive acetogenesis can be stimulated in ruminal samples during short-term (24-h) incubations when methanogenesis is inhibited selectively. While addition of the reductive acetogen Peptostreptococcus productus ATCC 35244 alone had no significant influence on CH4 and volatile fatty acid (VFA) production in ruminal samples, the addition of this strain together with 2-bromoethanesulfonic acid (BES) (final concentration, 0.01 or 0.03 mM) resulted in stimulation of acetic acid production and H2 consumption. Since acetate production exceeded amounts that could be attributed to reductive acetogenesis, as measured by H2 consumption, it was found that P. productus also fermented C6 units (glucose and fructose) heterotrophically to mainly acetate (> 99% of the total VFA). Using 14CH3COOH, we concluded that addition of BES and BES plus P. productus did not alter the consumption of acetate in ruminal samples. The addition of P. productus to BES-treated ruminal samples caused supplemental inhibition of CH4 production and stimulation of VFA production, representing a possible energy gain of about 13 to 15%.

Antagonistic effects of sulfide and butyrate on proliferation of colonic mucosa: a potential role for these agents in the pathogenesis of ulcerative colitis

It has been shown that feces of patients with ulcerative colitis uniformly contain sulfate reducing bacteria. Sulfide produced by these bacteria interferes with butyrate-dependent energy metabolism of cultured colonocytes and may be involved in the pathogenesis of ulcerative colitis. Mucosal biopsies from the sigmoid rectum of 10 patients (no caner, polyps, inflammatory bowel disease) were incubated with either NaCl, sodium hydrogen sulfide (1 mmol/L), a combination of both sodium hydrogen sulfide and butyrate (10 mmol/L), or butyrate. Mucosal proliferation was assessed by bromodeoxyuridine labeling of cells in S-phase. Compared to NaCl, sulfide increased the labeling of the entire crypt significantly, by 19% (p < 0.05). This effect was due to an expansion of the proliferative zone to the upper crypt (compartments 3-5), where the increase in proliferation was 54%. Sulfide-induced hyperproliferation was reversed when samples were coincubated with sulfide and butyrate. The study shows that sodium hydrogen sulfide induces mucosal hyperproliferation. Our data support a possible role of sulfide in the pathogenesis of UC and confirm the role of butyrate in the regulation of colonic proliferation and in the treatment of UC.

Gastro-enteric methane versus sulphate and volatile fatty acid production

The breakdown of low digestible components present in food during passage through the human and animal gastro-intestinal (GI) tract is performed by the highly diverse microbial community present in this ecosystem. Fermentation of these substances yields, besides CO2 and volatile fatty acids, H2, which is used as a substrate by three different H2-consuming bacteria. Sulphate-reducing bacteria (SRB) use H2 to reduce SO inf4 (sup2-) to H2S, hydrogenotrophic methane-producing bacteria (MPB) use H2 to reduce CO2 to CH4 and reductive acetogens (RAC) use H2 to reduce CO2 to CH3COOH. A competition between these three bacterial groups exists for the common H2 substrate. This results generally in the dominance of one group above the other two.

The rumen and hindgut as source of ruminant methanogenesis

The advantage of ruminants is their ability to convert fibrous biomass to high quality protein for human nutrition purposes. Rumen fermentation, however, is always associated with the formation of methane - a very effective greenhouse gas. Hindgut fermentation differs from rumen fermentation by a substantially lower methane production and the presence of reductive acetogenesis or dissimilatory sulfate reduction. Sulfate reduction and methanogenesis seem to be mutually exclusive, while methanogenesis and reductive acetogenesis may occur simultaneously in the hindgut. Although acetogenic bacteria have been isolated from the bovine rumen, methanogenesis prevails in the forestomachs. The substitution of acetate for methane as a hydrogen sink in the rumen should increase energy yield for the animal and decrease methane emissions into the environment. Differences in the major hydrogen sinks in both microbial ecosystems are discussed and mainly related to differences in substrate availability and to the absence of protozoa in the hindgut.

Methanogenesis in monogastric animals

Studies of methanogenic bacteria present in monogastric animals are still scarce. Methanogens have been isolated from faeces of rat, horse, pig, monkey, baboon, rhinoceros, hippopotamus, giant panda, goose, turkey and chicken. The predominant methanogen in all except the chicken and turkey is species of Methanobrevibacterium. The chicken and turkey harbour species of Methanogenium. In pig the population of methanogenic bacteria is more than 30 times as dense in the distal colon as in the caecum. This finding is in agreement with the finding that the rate of methane production is much higher in the colon than in the ceacum. The amount of methane excreted clearly seems to depend on the amount of non-starch polysaccharide intake.The directly measured methane production rate in pigs is from 3.3 to 3.8 times lower than the amount expected from stoichiometric estimates. These data, together with data showing that only small net amounts of hydrogen and small amounts of methane are produced in the ceacum and proximal colon where the microbial activity is high, clearly indicate that hydrogen sinks other than methane production are involved in hydrogen removal in the hindgut of pigs and probably also in other monogastric animals.Methane production by monogastric animals is lower than methane production by ruminants. However, methane production by large herbivorous monogastric animals such as horses, mules and asses is substantial (up to 80 l per animal per day). Methane production by rodents and avians is low. In general, methane production by wild animals is lower than methane production by domestic animals. It is concluded that the contribution of monogastric animals to the global methane emission is negligible, as it only represent about 5% of the total methane emission by domestic and wild animals of 80 Tg per year.

Ashkenazi Jews, sulfur gases, and ulcerative colitis

Fecal pathogens have been suspected to cause ulcerative colitis, yet none have been identified. Meanwhile, the 400 species comprising normal colonic flora have received little attention as potential pathogens. Sulfate-reducing bacteria (SRB), a frequent colonic commensal, have been identified in greater numbers in people with ulcerative colitis. The bacteria produce hydrogen sulfide, a toxic compound with the potential to cause colonic injury and possibly ulcerative colitis. If these bacteria are pathogenic, high-risk populations may harbor greater numbers of these organisms in their colons. We compared a group with a high incidence of ulcerative colitis, Ashkenazi Jews, to a control population to assess carriage rates for SRB. Breath samples were collected to indirectly determine colonic conditions. No difference was found between the two groups studied.

Relations between transit time, fermentation products, and hydrogen consuming flora in healthy humans

BACKGROUND/AIMS

To investigate whether transit time could influence H2 consuming flora and certain indices of colonic bacterial fermentation.

METHODS

Eight healthy volunteers (four methane excretors and four non-methane excretors) were studied for three, three week periods during which they received a controlled diet alone (control period), and then the same diet with cisapride or loperamide. At the end of each period, mean transit time (MTT) was estimated, an H2 lactulose breath test was performed, and stools were analysed.

RESULTS

In the control period, transit time was inversely related to faecal weight, sulphate reducing bacteria counts, concentrations of total short chain fatty acids (SCFAs), propionic and butyric acids, and H2 excreted in breath after lactulose ingestion. Conversely, transit time was positively related to faecal pH and tended to be related to methanogen counts. Methanogenic bacteria counts were inversely related to those of sulphate reducing bacteria and methane excretors had slower MTT and lower sulphate reducing bacteria counts than non-methane excretors. Compared with the control period, MTT was significantly shortened (p < 0.05) by cisapride and prolonged (p < 0.05) by loperamide (73 (11) hours, 47 (5) hours and 147 (12) hours for control, cisapride, and loperamide, respectively, mean (SD)). Cisapride reduced transit time was associated with (a) a significant rise in faecal weight, sulphate reducing bacteria, concentrations of total SCFAs, and propionic and butyric acids and breath H2 as well as (b) a significant fall in faecal pH and breath CH4 excretion, and (c) a non-significant decrease in the counts of methanogenic bacteria. Reverse relations were roughly the same during the loperamide period including a significant rise in the counts of methanogenic bacteria and a significant fall in those of sulphate reducing bacteria.

CONCLUSIONS

Transit time differences between healthy volunteers are associated with differences in H2 consuming flora and certain indices of colonic fermentation. Considering the effects of some fermentation products on intestinal morphology and function, these variations may be relevant to the pathogenesis of colorectal diseases.

Gastrointestinal gas formation and infantile colic

Gastrointestinal gas causes distress in many patients and their parents. Most often, patients do not have an actual increase in gastrointestinal gas volume, but rather their complaints derive from a misunderstanding of normal physiology, a misinterpretation of symptoms (colic), or an increase in intestinal sensitivity (irritable bowel syndrome). Symptoms from actual increases in intestinal gas volume are seen most frequently in children who swallow excessive amounts of air, have a dysmotility syndrome, or consume foods containing poorly absorbed carbohydrates. Although many therapies are used in the treatment of gas-related symptoms, under close scrutiny, the commonly recommended agents (e.g. simethicone) do not have proven efficacy. An understanding of the physiology of gas production and disposal is of practical use to pediatricians in determining the appropriate method of intervention for patients with these complaints.

Effect of two levels of transgalactosylated oligosaccharide intake in rats associated with human faecal microflora on bacterial glycolytic activity, end-products of fermentation and bacterial steroid transformation

The effects of two levels of transgalactosylated oligosaccharide (TOS) intake on bacterial glycolytic activity, end products of fermentation and bacterial steroid transformation were studied in rats associated with a human faecal flora. Rats were fed a human-type diet containing 0, 5 or 10% TOS. Caecal pH decrease correlated with the amount of TOS in the diet. Intake of the TOS diet induced a decrease in blood cholesterol and a strong increase in beta-galactosidase activity in the hindgut. TOS fermentation led to production of hydrogen and short chain fatty acids, whereas ammonia and branched-chain fatty acids were decreased. A diet containing 10% TOS increased caecal lactic acid concentrations and reduced beta-glucuronidase activities and steroid transformation.

Colonic fermentation of complex dietary carbohydrates in short-bowel patients. No association with hydrogen excretion and fecal and plasma short-chain fatty acids

BACKGROUND

The colonic degradation of carbohydrates (fermentation) to short-chain fatty acids (SCFAs) appears to have major impacts on colonocyte function, sodium and water absorption, and large-bowel energy salvation, but how to quantify the in vivo fermentation in man is still debatable.

METHODS

Indicators of colonic fermentation, fecal and plasma SCFAs and breath hydrogen (H2), were measured in 10 short-bowel patients (mean +/- SE; 106 +/- 21 cm) with totally preserved large bowels who were on a 60% high-carbohydrate, 20% low-fat diet, compared with the reversed isocaloric 20% low-carbohydrate, 60% high-fat diet. This human model showed large differences in large-bowel fermentation, as excretions of calories were reduced (40%; 485 +/- 151 kcal/day) and excretions of carbohydrates were unchanged and low with the high-carbohydrate diet as compared with the low-carbohydrate diet, in contrast to unchanged calorie excretion in short-bowel patients with no colonic function.

RESULTS

Fecal concentrations of SCFAs did not change when the diet was changed from the high content to the low content of carbohydrates (82 +/- 11 mmol/l and 79 +/- 9 mmol/l, respectively). The ratio of acetate in feces increased (from 48 +/- 4% to 54 +/- 3%; p = 0.01) on the high-carbohydrate diet, whereas the percentage of the other SCFAs decreased proportionally. Plasma SCFAs 2 h and 6 h after breakfast were also identical when comparing the two dietary regimens. Nor were the peak H2 breath excretion and the area under the H2 excretion-versus-time curve increased by the threefold increase in the intake of dietary carbohydrates.

CONCLUSIONS

Fecal and plasma SCFAs and breath H2 excretion are of limited value in the evaluation of even large differences in colonic fermentation of complex dietary carbohydrates.

Echo-planar magnetic resonance imaging to assess water volume in the distal small bowel

PURPOSE

Assessment of fluid volumes and flow through the small intestine has in the past only been possible by means of invasive intubation studies on human volunteers. Intubation very likely disturbs gut motility and stimulates secretion.

METHODS

The aim of this study was to utilise the new technique of echo-planar magnetic resonance imaging in order to non-invasively visualise the changing volume of water in the small intestinal lumen. 200 mls of test solution was ingested and water volume assessed using a multi-slice scanning technique on 3 separate days. The solutions were pure water, pure water plus 2.264 or 10 g of mannitol. These were taken on separate days by 8 healthy male volunteers. Regions of interest were constructed in the area of the lower pelvis excluding retroperitoneal structure.

RESULTS

The water content of the lower small intestine did not change significantly over the 4 hours after the control solution. By contrast after both mannitol solutions there was an increase in the amount of water in the distal intestine as assessed by the area under the curve of the volume time profile (Control 51 ml.h (SD +/- 47); mannitol 2.264 g/200 ml 72 ml.h (SD +/- 57); 10 g/200 ml mannitol 115 ml.h (SD +/- 56)). Page's L Trend test showed that the trend for the volume to increase with increasing mannitol concentration to be statistically significant at the 1% level (L = 108).

CONCLUSIONS

The study highlights the potential of echo-planar magnetic resonance imaging to visualise changes in gastrointestinal physiology in a noninvasive manner.

A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance

BACKGROUND

Ingestion of a large dose of the milk sugar lactose--for example, the 50-g load in 1 liter of milk--causes symptoms such as abdominal pain, diarrhea, bloating, and flatulence in the majority of people with lactose malabsorption. It is uncertain whether the ingestion of more common doses of lactose, such as the amount in 240 ml (8 oz) of milk, causes symptoms. Some people insist that even smaller quantities of milk, such as the amount used with cereal or coffee, cause severe gastrointestinal distress.

METHODS

In a randomized, double-blind, crossover trial, we evaluated gastrointestinal symptoms in 30 people (mean age, 29.4 years; range, 18 to 50) who reported severe lactose intolerance and said they consistently had symptoms after ingesting less than 240 ml of milk. The ability to digest lactose was assessed by measuring the subjects' end-alveolar hydrogen concentration after they ingested 15 g of lactose in 250 ml of water. Subjects then received either 240 ml of lactose-hydrolyzed milk containing 2 percent fat or 240 ml of milk containing 2 percent fat and sweetened with aspartame to approximate the taste of lactose-hydrolyzed milk; each type of milk was administered daily with breakfast for a one-week period. Using a standardized scale, subjects rated the occurrence and severity of bloating, abdominal pain, diarrhea, and flatus and recorded each passage of flatus.

RESULTS

Twenty-one participants were classified as having lactose malabsorption and nine as being able to absorb lactose. During the study periods, gastrointestinal symptoms were minimal (mean symptom-severity scores for bloating, abdominal pain, diarrhea, and flatus between 0.1 and 1.2 [1 indicated trivial symptoms; and 2, mild symptoms]). When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms. For the lactose-malabsorption group, the mean (+/- SEM) difference in episodes of flatus per day was 2.5 +/- 1.1 (95 percent confidence interval, 0.2 to 4.8). Daily dietary records indicated a high degree of compliance, with no additional sources of lactose reported.

CONCLUSIONS

People who identify themselves as severely lactose-intolerant may mistakenly attribute a variety of abdominal symptoms to lactose intolerance. When lactose intake is limited to the equivalent of 240 ml of milk or less a day, symptoms are likely to be negligible and the use of lactose-digestive aids unnecessary.

Pneumatosis cystoides intestinalis and high breath H2 excretion: insights into the role of H2 in this condition

Patients with pneumatosis cystoides intestinalis have been reported to excrete excessive H2 because of a lack of H2-consuming intestinal bacteria. This study describes a patient with bacterial overgrowth and pneumatosis of the small intestine whose colonic flora avidly consumed H2 but whose small bowel flora produced but did not consume H2. There is no commonly accepted mechanism whereby excessive luminal H2 causes intramural gas. An explanation is proposed in which an initial, transitory source of intramural gas is distinguished from the mechanism that results in the persistence of the gas. Independent of the initial source of gas, rapid diffusion of H2 from the lumen into an intramural gas bubble would cause N2, O2, and CO2 to diffuse from the blood into the bubble. As a result, the bubble would expand and then persist indefinitely as long as H2 continued to diffuse from the lumen to the intramural gas collection.

Validation of weighed records and other methods of dietary assessment using the 24 h urine nitrogen technique and other biological markers

Results from analysis of 24 h urine collections, verified for completeness with para-amino benzoic acid, and blood samples collected over 1 year were compared with 16 d weighed records of all food consumed collected over the year, and with results from 24 h recalls, food-frequency questionnaires and estimated food records in 160 women. Using the weighed records, individuals were sorted into quintiles of the distribution of the urine N excretion:dietary N intake ratio (UN:DN). UN exceeded DN in the top quintile of this ratio; mean ratio UN:DN = 1.13. Individuals in this top quintile were heavier, had significantly greater body mass indices, were reportedly more restrained eaters, had significantly lower energy intake:basal metabolic rate ratios (EI:BMR), and had correlated ratios of UN:DN and EI:BMR (r -0.62). Those in the top quintile reported lower intakes of energy and energy-yielding nutrients, Ca, fats, cakes, breakfast cereals, milk and sugars than individuals in the other quintiles but not lower intakes of non-starch polysaccharides, vitamin C, vegetables, potatoes or meat. Correlations between dietary intake from weighed records and 24 h urine K were 0.74 and 0.82, and between dietary vitamin C and beta-carotene and plasma vitamin C and beta-carotene 0.86 and 0.48. Correlations between dietary N intake from weighed records and 24 h urine excretion were high (0.78-0.87). Those between N from estimated food records and urine N were r 0.60-0.70. Correlations between urine N and 24 h recalls and food-frequency questionnaires were in the order of 0.01 to 0.5. Despite problems of underreporting in overweight individuals in 20% of this sample, weighed records remained the most accurate method of dietary assessment, and only an estimated 7 d diary was able to approach this accuracy.

Replacement of digestible by resistant starch lowers diet-induced thermogenesis in healthy men

The present study describes the effect of replacement of digestible starch by resistant starch (RS) on diet-induced thermogenesis (DIT), postprandial glucose and insulin responses, and colonic fermentation. Ten healthy males consumed three test meals, consisting of diluted, artificially-sweetened fruit syrup and either 50 g raw potato starch (550 g RS/kg), or 50 g pregelatinized potato starch (0 g RS/kg) or 30 g pregelatinized potato starch plus 20 g lactulose (670 g indigestible disaccharide/kg). The meals were served in the morning after an overnight fast. Each volunteer consumed each meal twice on six separate days in random order. Metabolic rate was measured by indirect calorimetry in the fasting state for 15 min and postprandially for 5 h. Shortly before and hourly up to 7 h after consumption of the test meal, end-expiratory breath samples were obtained for H2 and CH4 analysis. Shortly before the meal and 30, 60, 180, and 300 min postprandially, blood samples were taken for glucose and insulin analyses. Postprandial increases in glucose and insulin levels were proportional to the amount of digestible carbohydrate in the meal. Breath H2 and CH4 concentrations indicated that the pregelatinized starch was not fermented and that lactulose was fermented rapidly. Fermentation of the raw starch started only 6 to 7 h after consumption, resulting in a rise in breath H2 but not in CH4. The replacement of 27 g digestible starch by RS in a single meal lowered DIT by on average 90 kJ/5 h, as could also be calculated by assuming that RS does not contribute to DIT. The ingestion of lactulose resulted in a substantial rise in DIT which was most probably caused by its fermentation.

Malnutrition in the developing and developed world: is small intestinal bacterial colonization important?

Malnutrition is a major problem on a global basis and will continue if current world population trends persist. Small intestinal bacterial colonization may contribute to malnutrition in populations whose dietary intake is marginal, such as those in developing countries and many elderly in the developed world. This review focuses on the evidence for small intestinal bacterial colonization in these subjects and briefly revises current thinking on the pathogenesis and diagnosis of this condition.

Methanogens outcompete sulphate reducing bacteria for H2 in the human colon

Methanogens and sulphate reducing bacteria compete for H2 in the human colon, and, as a result, faeces usually contain high concentrations of just one of these two organisms. There is controversy over which of these organisms wins the competition for H2, although theoretical data suggest that sulphate reducing bacteria should predominate. To elucidate this question experiments were undertaken in which sulphate enriched homogenates of human sulphate reducing faeces and methane producing faeces were incubated separately or mixed together. Co-incubation of sulphate reducing faeces with methanogenic faeces resulted in a sixfold reduction in the activity of the sulphate reducing bacteria (measured as sulphide production), whereas methane production was not inhibited by co-incubation with sulphate reducing bacteria. Methanogenic faeces also consumed H2 more rapidly and reduced the H2 tension of the homogenate to a lower value than did sulphate reducing faecal samples. In these experiments, methanogens seem to outcompete sulphate reducing bacteria for H2.

Intracellular Campylobacter-like organism from ferrets and hamsters with proliferative bowel disease is a Desulfovibrio sp

Proliferative bowel disease is an intestinal disorder of a variety of domestic animals associated with the presence of an intracellular Campylobacter-like organism (ICLO). We have identified the ICLO obtained from a ferret with proliferative colitis by 16S rRNA sequence analysis. In this ferret, proliferative bowel tissue containing the ICLO had translocated to the mesenteric lymph nodes, omentum, and liver. The 16S rRNA genes of the ICLO were amplified from an infected fragment of extraintestinal tissue by using universal prokaryotic primers. Approximately 1,480 bases of the amplified 16S rRNA gene were sequenced by cycle sequencing. Comparison of the sequence of the ICLO with those of over 400 bacteria in our data base indicated that the sequence of the ICLO was most closely related to that of Desulfovibrio desulfuricans (87.5% similarity). Phylogenetic analysis with 12 Desulfovibrio species and 20 species from related genera placed the ICLO in a subcluster within the genus Desulfovibrio with D. desulfuricans and 5 other Desulfovibrio species. We will refer to this organism as the intracellular Desulfovibrio organism (IDO). Specific primers were produced for PCR amplification of a 550-base fragment of the 16S rRNA gene of the IDO in proliferative intestinal tissue samples. This unique 550-base segment was amplified from samples of frozen intestinal tissue from nine ferrets and three hamsters with ICLO-associated disease but not in four intestinal tissue samples from animals without the ICLO-associated disease. The 550-base amplified products from the bowel tissues of one hamster and one ferret were fully sequenced. The ferret IDO partial sequence was identical to the previously determined 16S rRNA sequence over its length, and the hamster IDO sequence differed by a single base. The same intracellular organism has been identified in proliferative intestinal tissues of swine and that the organism has been successfully maintained in tissue culture. The availability of specific primers for PCR-based detection of this intracellular Desulfovibrio organism will aid in the determination of its role in the pathogenesis of proliferative bowel disease in a variety of infected hosts.

Study of constancy of hydrogen-consuming flora of human colon

The constancy of the hydrogen consuming flora of the human colon was studied in 15 healthy subjects via two measurements obtained 18 to 36 months apart. Hydrogen disappearance rate and the major products of H2-consuming bacteria, methane and sulfide, were measured during incubation of fecal homogenates with excess hydrogen and sulfate. In 11/15, the hydrogen consumption rate and the predominant hydrogen-consuming pathway (methanogenesis, sulfate reduction, or neither) remained constant. However, major shifts in these pathways were observed in four subjects, with two losing and two gaining the ability to produce methane. Methanogenesis was associated with the highest hydrogen consumption rate. This study demonstrates that clinically unrecognizable, major alterations of the colonic flora occur in healthy subjects. Understanding of the factors responsible for these alterations might allow for therapeutic manipulation of the colonic flora.

A possible role for bile acid in the control of methanogenesis and the accumulation of hydrogen gas in the human colon

This study investigated a possible role for primary bile acid in the control of methanogenesis in the human colon. Production of hydrogen and methane was measured in anaerobic faecal cultures derived from faeces of six 'non-methanogenic' and three methanogenic healthy humans. Using a sensitive technique for gas measurement, methane was detected in all faecal cultures, including those from 'non-methanogenic' humans. Bile acid inhibited methanogenesis in a dose-response fashion in the in vitro 'non-methanogenic' and methanogenic faecal cultures. Inhibition was significant at bile acid concentrations > 0.05%. Methanogenesis correlated with methanogen (methanogenic bacteria) numbers. If this inhibition occurs in vivo, then it would explain much of the epidemiology of non-methanogenesis in humans. From an analysis of net hydrogen production by the faecal cultures, it is inferred that bile acid inhibits other hydrogen-consuming bacteria in addition to methanogens. These in vitro data suggest a major role for bile acid in the accumulation of hydrogen gas in the colon. Possible links between bile acid induced accumulation of gas and irritable bowel syndrome are discussed.

Prevalence and consistency of low breath H2 excretion following lactulose ingestion. Possible implications for the clinical use of the H2 breath test

The clinical use of the H2 breath test is limited by the finding that a variable fraction of the population fails to excrete appreciable H2 during colonic carbohydrate fermentation. Therefore, we assessed the ability to increase breath H2 excretion in 371 patients (224 female, 147 male) by administering the nonabsorbable sugar lactulose. Following 12g of lactulose, 27% of 94 patients did not increase their breath H2 concentration over 20 ppm and were considered low H2 excretors. Ingestion of 20 g of lactulose in 277 patients yielded a frequency of low H2 excretors of 14%. Six of 10 patients that were low H2 excretors after 12g of lactulose increased their breath H2 levels over 20 ppm when tested with 20g. In 35 patients tested with the same amount of lactulose on two separate occasions, the subject frequently altered his or her H2 producing status over a period of a few weeks. Low H2 excretors had a significantly higher breath CH4 concentration, both fasting (22 +/- 34 ppm) and after lactulose (51 +/- 58 ppm) compared to the remaining patients (5 +/- 13 ppm and 16 +/- 40 ppm, respectively). While the mean age of low excretors (54 +/- 17 years) was significantly higher than the others (44 +/- 17 years), no difference was found for sex prevalence and stool pH. This study demonstrates that respiratory H2 excretion following lactulose ingestion is not consistent and suggests that the application of too restrictive criteria could lead to improper interpretation of the H2 breath test.

Pyxigraphic sampling to enumerate methanogens and anaerobes in the right colon of healthy humans

BACKGROUND

A major limitation in studying the proximal human colonic flora is the lack of suitable sampling methods. The aim of this study was (1) to describe a prototype technique, pyxigraphy, which uses swallowed capsules containing a mechanism allowing the remote control of sampling the gastrointestinal tract contents, and (2) to use this sampling method to examine the distribution of methanogens in the colon of methane (CH4) excretors and non-CH4 excretors.

METHODS

In six CH4 excretors and four non-CH4 excretors, samples of the right colonic contents were obtained by means of the pyxigraphic sampling method. Methanogens and total anaerobes were enumerated in both the right colonic and fecal contents.

RESULTS

In CH4 excretors, the concentration of methanogens was higher in the feces than in the right colonic contents, representing 12% and 0.003%, respectively, of the total anacrobes (P < 0.02). In non-CH4 excretors, no difference was observed, methanogens representing < 0.003% of the total anaerobes in both the right colonic and fecal contents.

CONCLUSIONS

Pyxigraphy is a noninvasive, simple, and safe sampling method that allows to study the microbial populations of the proximal colon. The results obtained showed that methanogens preferentially colonize the distal part of the colon in CH4 excretors.

Gastrointestinal responses to oats consumption in young adult and elderly rats: digestion, large bowel fermentation and crypt cell proliferation rates

The present experiment was designed to test the hypothesis that ageing modifies the gastrointestinal responses to a change in diet composition. Rats of the Wag/Rij strain, either young adult (4 months of age) or elderly (27 months of age), were given a basal semi-purified diet or a diet of similar major nutrient composition containing 500 g oatmeal/kg for 17-18 d. Elderly rats digested the dry matter (DM) and organic matter (OM) of both diets less well than did their young adult counterparts, with more of this digestion occurring in the distal intestine. The greater flow of OM to the caecum of oats-fed animals was accompanied by significant reductions in caecal pH and increases in caecal total short-chain fatty acids (SCFA) concentration which appeared to be independent of age. However, young adults responded to feeding on oats by showing a much larger increase in the molar proportion of butyrate (332%) than did elderly animals (79%). Elderly rats had longer duodenal villi than did young adults but effects of age or diet were not detectable at other sites. With both age-groups oats consumption was associated with significant stimulation of crypt cell proliferation rate (CCPR) in the small intestine and caecum, but for the colon there was a significant reduction in CCPR with oats feeding. A reduced ability of the aged large bowel (LB) to produce butyrate may contribute to the prevalence of LB disorders in the elderly.

Colonic hydrogen absorption: quantification of its effect on hydrogen accumulation caused by bacterial fermentation of carbohydrates

The aim of the study was to assess (quantitatively) colonic hydrogen absorption. Hydrogen volumes in flatus and breath were measured over periods of six hours in normal subjects during fasting and after ingestion of the non-absorbable carbohydrate lactulose to simulate the effect of fermentable dietary fibres. If less than 76 ml/6 h of hydrogen accumulated in the colon then all of it was absorbed, as suggested by the intercept of the regression line of the correlation between hydrogen volumes in flatus and breath after ingestion of lactulose. As total flatus volume increased, efficiency of colonic hydrogen absorption decreased from 90% to 20%. The positive correlation between hydrogen volumes of flatus and breath showed that the eightfold interindividual differences in flatus volume after ingestion of 12.5 g of lactulose were caused by differences in bacterial net gas production, not gas absorption. Differences in colonic gas emptying rate are the consequence rather than the cause of interindividual differences in flatus volume.

IN CONCLUSION

(1) colonic hydrogen absorption is highly effective at low colonic hydrogen accumulation rates, but not at higher accumulation rates; (2) ineffective colonic gas absorption is the consequence and not the cause of high colonic gas accumulation rate after ingestion of non-absorbable carbohydrates; and (3) future therapeutic approaches to the large interindividual variability in colonic gas accumulation after ingestion of poorly absorbable fermentable carbohydrates, such as some kinds of dietary fibres, should be directed towards altering colonic bacterial metabolism.

Relationship between methane production and breath hydrogen excretion in lactose-malabsorbing individuals

Recent studies have shown reduced breath hydrogen (H2) excretion in methane (CH4)-producing healthy individuals following ingestion of lactulose. This questions the reliability of the breath hydrogen test (BHT) in CH4 excretors, but the relationship between CH4 and H2 excretion in other clinical applications of the BHT is not known. We reviewed BHT results in two groups of subjects: (1) 385 children tested for lactose malabsorption in a hospital setting, and (2) 109 lactose-malabsorbing patients tested with a home kit. The percentage of lactose malabsorbers in group 1 (51%) was the same regardless of CH4-producing status (P = 0.97). The BHT data from group 2 showed a positive correlation (r = 0.6, P < 0.000001) between the magnitude of the rise in CH4 and H2 concentrations, and the H2 excretion curves were significantly higher in the CH4-producing individuals. We conclude that attention to CH4-producing status is not necessary in the interpretation of the lactose BHT.