Influence of a Methanogenic Flora on the Breath H2 and Symptom Response to Ingestion of Sorbitol or Oat Fiber

Background and Objectives: We investigated the possibility that a variant of the normal colonic flora, a high concentration of methanogeas, influences the host's response to ingestion of nonabsorbable, fermentable materials. Methods: To better evaluate symptomatic and breath H₂ and methane (CH₄) responses, subjects were placed on a basal diet (primarily rice and hamburger) that contained minimal amounts of nonabsorbable, fermentable substrate. A breath CH₄/H₂ ratio of greater or less than 1 on the second day of the basal diet was used to categorize subjects as high (N = 9) or low (N = 25) CH₄ producers. After stabilization of the breath gas excretion (day 3 or 4 on the basal diet), the subjects ingested either sorbitol (8.8 g) or oat fiber (10.2 g). Results: The low CH₄ producers had a signficantly higher ( p < 0.05) breath H₂ concentration than the high producers on the basal diet and after ingestion of sorbitol (27.1 ± 2.7 ppm vs 15.8 ± 3.6 ppm) or oat fiber (13.1 ± 0.08 ppm vs 9.6 ± 1.2 ppm). Low producers of methane reported significantly increased bloating and cramping after sorbitol ingestion and increased bloating after fiber ingestion, whereas high CH₄ producers reported no signficant increase in these symptoms. Conclusion: The presence of a methanogenic flora is associated with a reduced symptomatic response to ingestion of nonabsorbable, fermentable material in healthy subjects. Manipulation of the normal flora could be of therapeutic value in nonmethanogenic patients with irritable bowel syndrome.     

Incidence of Predominant Methanogenic Flora in Irritable Bowel Syndrome Patients and Apparently Healthy Controls from North India

Background Flatulence is a common symptom in patients with irritable bowel syndrome (IBS). This may be due to production of hydrogen by intestinal flora. With the presence of methanogenic flora, 4 mol of hydrogen (H₂) are used with 1 mol of carbon dioxide (CO₂) to produce 1 mol of methane (CH₄), a process greatly reducing the volume of gas in the colon. However, the prevalence of methanogenic flora has not yet been reported in healthy and IBS patients from North India. Therefore, this study was planned. Methods This study was conducted prospectively and included 345 patients with irritable bowel syndrome (fulfilling Rome II criteria) and 254 age- and gender-matched apparently healthy controls. Each subject underwent a hydrogen breath test using 10 g lactulose after an overnight fast. An SC Microlyser from Quintron, USA, was used to measure methane and hydrogen at baseline and at every 30 min for 4 h. Subjects with fasting methane concentration <10 p.p.m. were labeled as low methane producers (LMPs) and > 10 p.p.m. as predominant methane producers (PMPs). Results The IBS and control groups included 66.78% and 67.53% men, respectively. Mean age in the two groups was 48.52 ± 30.54 years (range 15–68 years) and 45.67 ± 30.54 years (range 15–78 years), respectively. Prevalence of predominant methanogenic flora in IBS and control groups was 14.5% (50/345) and 34.6% (88/254), respectively (P < 0.001). Fifty-two out of 254 (20.6 %) were PMPs and 36 out of 254 (14.0%) were LMPs in controls. In contrast to this, IBS patients had 17 out of 354 (4.9%) that were PMPs and 33 out of 345 (9.6%) that were LMPs. Conclusion Methanogenic flora was significantly lower in IBS patients from North India than in apparently healthy subjects. This may be one of the causes of flatulence in IBS patients.     

Effect of Predominant Methanogenic Flora on Outcome of Lactose Hydrogen Breath Test in Controls and Irritable Bowel Syndrome Patients of North India

The relationship between methanogenic flora and hydrogen (H₂) production is considered to be a possible confounding factor in the interpretation of hydrogen breath tests (H₂BT). Therefore, the present study was conducted prospectively and included 154 IBS patients (fulfilling Rome II criteria) and 286 age-and-sex-matched apparently healthy controls. Each subject underwent H₂BT after overnight fasting using 25 g lactose. Methane and H₂ were measured using an SC Microlyser from Quintron, USA, at baseline and every 30 min for a total of 4 h. Subjects with fasting methane concentration <10 ppm were labeled as low methane producers (LMP) and >10 ppm as predominant methane producers (PMP). A rise >20 ppm over base line in hydrogen concentration was taken as +ve hydrogen breath test. IBS and control groups included 66.78% and 67.53% males, respectively. Mean age in the two groups were 48.52 ± 30.54 years (range 15–68 years) and 45.67 ± 30.54 years (range 15–78 years), respectively. Hydrogen breath test was +ve in 77/154 (50%) IBS patients and in 142/286 (49.65%) in controls (P > 0.05). It was also observed that the hydrogen breath test was −ve due to PMP in 5/77 (6.49%) of IBS patients and in 29/154 (20.14%) in controls. PMP affected lactose hydrogen breath tests in 6.49–20.14% subjects. This effect is more apparent in apparently healthy subjects as compared to patients with IBS.     

Breath methane associated with slow colonic transit time in children with chronic constipation

OBJECTIVE: This study analyzed the relationship between methane production and colonic transit time in children with chronic constipation. METHODOLOGY: Forty children, from 3 to 13 years of age, suffering from chronic constipation were included. Methane production was defined when the breath methane concentration was greater than 3 ppm. The total and segmental colonic transit times were measured with radio-opaque markers. RESULTS: Soiling was present in 34 (85.0%) of 40 patients with constipation. Methane production was present in 25 of 34 (73.5%) patients with constipation and soiling and only in 1 (16.7%) of 6 with constipation but without soiling (P = 0.014). The medians of total colonic transit time were 80.5 and 61.0 hours, respectively (P = 0.04), in methane and nonmethane producers. Segmental colonic transit times were 17.5 and 10.5 hours, respectively (P = 0.580), in right colon, 29.5 and 10.5 hours (P = 0.001), respectively, in left colon, and 31.5 and 27.0 hours (P = 0.202), respectively, in the rectosigmoid. By the sixth week of treatment, the reduction in the total colonic transit time was greater in patients who had become nonmethane producers. CONCLUSION: The presence of breath methane in children with chronic constipation may suggest the possibility of prolonged colonic transit time.     

Breath methane in children with chronic constipation

RATIONAL: Methane is an intestinal gas which may be excreted in the expired air of about 10% of children. OBJECTIVE: The aims of this study were to investigate methane production by children with functional chronic constipation and methane concentration in the expired air before and after a bowel movement induced by a phosphate enema. METHODS: Seventy-five patients with functional chronic constipation aged from 3 to 13 years were studied. Methane concentration in the expired air was determined using a gas chromatograph (Quintron, model 12i). Methane production was considered present if the breath methane concentration was equal or greater than 3 ppm. RESULTS: Methane production was present in 44 (86.3%) of 51 patients with constipation and fecal soiling versus only 7 (29.2%) of 24 patients with constipation without fecal soiling. After six weeks of therapy for constipation, the number of methane producers decreased by 65.2%. None of the 10 children with normal intestinal habit produced methane. Expired air methane concentration was determined before and after a bowel movement induced by a phosphate enema in 20 patients with impacted stool. From these 20 patients, 12 were methane producers. The median (percentiles 25 and 75 between parenthesis) of methane concentration decreased from 21.5 (15.0-25.5) ppm before to 11.0 (4.0-12.5) ppm after the bowel movement. CONCLUSION: Methane production was associated with chronic constipation with soiling and decreased when impacted stool decreased.     

Carbohydrate Malabsorption: Quantification by Methane and Hydrogen Breath Tests

Rumessen JJ, Nordgaard-Andersen I, Gudmand-Høyer E. Carbohydrate malabsorption: quantification by methane and hydrogen breath tests. Scand J Gastroenterol 1994;29:826-832.

Background: Previous studies in small series of healthy adults have suggested that parallel measurement of hydrogen and methane resulting from gut fermentation may improve the precision of quantitative estimates of carbohydrate malabsorption. Systematic, controlled studies of the role of simultaneous hydrogen and methane measurements using end-expiratory breath test techniques are not available. Methods: We studied seven healthy, adult methane and hydrogen producers and seven methane non-producers by means of end-expiratory breath test techniques. Breath gas concentrations and gastrointestinal symptoms were recorded at intervals for 12 h after ingestion of 10,20, and 30 g lactulose. Results: In the seven methane producers the excretion pattern was highly variable; the integrated methane responses were disproportional and not reliably reproducible. However, quantitative estimates of carbohydrate malabsorption on the basis of individual areas under the methane and hydrogen excretion curves (AUCs) tended to improve in methane producers after ingestion of 20 g lactulose by simple addition of AUCs of methane to the AUCs of the hydrogen curves. Estimates were no more precise in methane producers than similar estimates in non-producers. Gastrointestinal symptoms increased significantly with increasing lactulose dose; correlation with total hydrogen and methane excretion was weak. Conclusions: Our study suggests that in methane producers, simple addition of methane and hydrogen excretion improves the precision of semiquantitative measurements of carbohydrate malabsorption. The status of methane production should, therefore, be known to interpret breath tests semiquantitatively. The weak correlation between hydrogen and methane excretion and gas-related abdominal complaints suggests that other factors than net production of these gases may be responsible for the symptoms.     

Respiratory methane excretion in children with lactose intolerance

Two evaluate the relationship between colonic methane production and carbohydrate malabsorption, we measured end-expiratory methane levels in 70 normal and 40 lactose-intolerant children. Time-dependent excretion of hydrogen and methane was determined every 30 min for 120 min following a fasting oral lactose challenge (2 g/kg). Mean breath hydrogen levels in normals (lactose-tolerant) equaled 3.7 parts per million (ppm) throughout the study, but increased to >10 ppm by 60 min and remained elevated in lactose-intolerant subjects. Breath methane in normal children averaged 1.6 ppm from 0 to 120 min. In contrast, CH₄ excretion by lactose-intolerant children averaged 5.1 ppm at 90 min; and, by 120 min levels increased significantly compared with control. Breath methane levels in lactose-intolerant subjects following a lactose load continued to increase, however, despite the coingestion of exogenous lactase in amounts calculated to result in complete hydrolysis of the disaccharide. These data demonstrate that lactase-deficient children manifest significant increases in breath methane excretion following lactose ingestion and that enhanced methane production may be a consequence of several factors, including altered fecal pH and increased methanogenic substrates provided by colonic lactose fermentation. Further studies are required to determine the clinical significance of elevated methane production in lactose intolerance.     

Breath Methane Excretion and Intestinal Methanogenesis in Children and Adults in Rural Nigeria

Breath methane excretion was measured in 274 healthy subjects from 2 rural communities in northern Nigeria. Studies in 24 adults showed a normal faecal flora with no enteric pathogens. Breath methane was detected in 122 (77%) of 159 adults, 19 (40%) of 47 older children (2-6 years), and 4 (8%) of 68 young children (<2 years). Women were slightly more commonly breath methane-positive than men (82% versus 75%, respectively). Hyperventilation did not influence the specificity of the breath methane assay, although levels were circa 30% lower after deliberate hyperventilation. Methanogens were estimated by enrichment culture of faeces from 49 subjects. Of the subjects 76% had faecal methanogens estimated at ≥10²/g, 45% at ≥10⁴/g, and 16% at ≥10⁶/g. There was no significant difference in distribution of methanogenic cultures between different age or tribal groups, and there were no obvious correlations between breath methane excretion and either the faecal carriage of methanogens per se or numbers present.     

Effect of Guar, Pectin, Psyllium, Soy Polysaccharide, and Cellulose on Breath Hydrogen and Methane in Healthy Subjects

Different types of dietary fiber are fermented to various extents in vitro, but little is known about the effects of fiber on breath hydrogen and methane levels in vivo. Therefore, we studied the effects on breath hydrogen and methane of 15 g of guar, pectin, psyllium, soy polysaccharide, or cellulose in eight healthy subjects over a 12-h period. None of the fibers had a significant effect on breath hydrogen or methane concentrations, compared with the control (fasting). The four methane producers had lower breath hydrogen levels than the nonproducers 1 h after 15 g of lactulose (3 +/- 1 vs. 42 +/- 9, p less than 0.005) and 5-12 h after the different fibers (3.3 vs. 4.8 ppm; pooled SEM = 0.8; p less than 0.025). When the methane responses of the methane producers were expressed as increments relative to the control, there were small differences between treatments, with guar producing a larger response, 8.2 +/- 3.3 ppm, than cellulose, -2.9 +/- 2.3 ppm (p less than 0.05). The incremental methane responses of the different fibers in vivo were related to the previously reported production of propionic acid (r = 0.94, n = 5, p less than 0.02) and methane (r = 0.93, n = 4, NS) from in vitro fermentation of the same fibers. We conclude that methane producers have lower breath hydrogen levels than nonproducers. Purified fermentable and nonfermentable dietary fibers have no effect on breath hydrogen levels over 12 h in subjects previously consuming a normal diet. However, fermentable fibers may produce small increases in breath methane in methane-producing subjects.     

Contributions of the microbial hydrogen economy to colonic homeostasis

Colonic gases are among the most tangible features of digestion, yet physicians are typically unable to offer long-term relief from clinical complaints of excessive gas. Studies characterizing colonic gases have linked changes in volume or composition with bowel disorders and shown hydrogen gas (H(2)), methane, hydrogen sulphide, and carbon dioxide to be by-products of the interplay between H(2)-producing fermentative bacteria and H(2) consumers (reductive acetogens, methanogenic archaea and sulphate-reducing bacteria [SRB]). Clinically, H(2) and methane measured in breath can indicate lactose and glucose intolerance, small intestinal bacterial overgrowth and IBS. Methane levels are increased in patients with constipation or IBS. Hydrogen sulphide is a by-product of H(2) metabolism by SRB, which are ubiquitous in the colonic mucosa. Although higher hydrogen sulphide and SRB levels have been detected in patients with IBD, and to a lesser extent in colorectal cancer, this colonic gas might have beneficial effects. Moreover, H(2) has been shown to have antioxidant properties and, in the healthy colon, physiological H(2) concentrations might protect the mucosa from oxidative insults, whereas an impaired H(2) economy might facilitate inflammation or carcinogenesis. Therefore, standardized breath gas measurements combined with ever-improving molecular methodologies could provide novel strategies to prevent, diagnose or manage numerous colonic disorders.     

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.     

Breath methane and large bowel cancer risk in contrasting African populations.

Breath methane has been measured in 1016 people from four populations resident in Southern Africa which experience widely different risks of bowel cancer and other colonic diseases. Highly significant differences in the proportion of subjects with detectable methane in breath were found; % producers--rural black 84, urban black 72, white 52, Indian 41 (chi 2 121 p less than 0.001 3 df). There was a slight preponderance of female producers over male (female producers 63%, males 57%) and an age trend with fewer producers in the older age groups in the urban blacks and Indians, these comparisons being significant when tested by stepwise logistic regression analysis. Bowel cancer risk, determined from a variety of sources, was lowest in rural blacks, greatest in whites, with intermediate rates for urban blacks and Indians. Methane production in the human colon shows significant interethnic differences but which bear no relation to bowel cancer risk in these populations.     

Role of colonic fermentation in the perception of colonic distention in irritable bowel syndrome and functional bloating.

BACKGROUND & AIMS: Bloating represents a frequent gastrointestinal symptom, but the pathophysiologic mechanism responsible for its onset is still largely unknown. Patients very frequently attribute the sensation of bloating to the presence of excessive bowel gas, but not all patients with gas-related symptoms exhibit increased intestinal production of gas. It is therefore possible that other still unrecognized mechanisms might contribute to its pathophysiology. Our aim was to evaluate whether a subgroup of patients affected by functional abdominal bloating presents hypersensitivity to colonic fermentation. METHODS: Sixty patients affected by functional gastrointestinal disorders (11 functional bloating, 36 constipation-predominant, and 13 diarrhea-predominant irritable bowel syndrome) and moderate to severe bloating took part in the study. Twenty sex- and age-matched healthy volunteers were enrolled as a control group. All the subjects underwent a preliminary evaluation of breath hydrogen excretion after oral lactulose. Then, on a separate day, an evaluation of sensitivity thresholds at rectal level was performed with a barostat before and after the induction of colonic fermentation with oral lactulose. A control test with electrolyte solution was also performed. RESULTS: Both breath hydrogen excretion and mouth-to-cecum transit time did not differ between the 4 groups studied. Neither electrolyte solution nor lactulose modified sensitivity thresholds in healthy volunteers. In low hydrogen producers, basal perception and discomfort thresholds were similar to high hydrogen producers, but after lactulose both perception and discomfort thresholds were significantly reduced only in low hydrogen producers. CONCLUSIONS: A subgroup of patients with functional gastrointestinal disorders and moderate to severe bloating might have hypersensitivity to products of colonic fermentation.     

Breath hydrogen response to lactulose in healthy subjects: relationship to methane producing status.

In order to assess the relationship between methane (CH4) producing status and the breath excretion of hydrogen (H2) in healthy subjects, breath CH4 and H2 were simultaneously measured for 14 hours after oral ingestion of 10 g lactulose in 65 young volunteers. Forty were breath CH4 producers and 25 were not. Statistically significant differences were observed between both groups, with lower values for CH4 producers recorded for the following parameters: fasting basal value of breath H2 (8.1 (4.9) v 5.2 (3.7) ppm, p less than 0.05), mouth-to-caecum transit time (68 (24) v 111 (52) min, p less than 0.005), and breath H2 production measured as area under the curve 13.1 (6.9) v 8.8 (3.8) 10(3) ppm/min, p less than 0.02). There was no significant correlation between individual production of breath H2 and CH4. These results indicate that the response to lactulose depends on breath CH4 producing status. In clinical practice, defining normal values of mouth-to-caecum transit time without knowledge of breath CH4 producing status may lead to misinterpretation of the H2 breath test.     

Breath hydrogen and methane levels in a patient with volvulus of the sigmoid colon

Volvulus of the large bowel is the third most common cause of colonic obstruction. A patient with colonic obstruction or delayed small intestinal transit may frequently have bacterial overgrowth and increased breath hydrogen (H(2)) and/or methane (CH(4)) excretion because the bacterium can contact with food residues for a longer time. A 39 year old woman attended our hospital with complaints of abdominal pain and distension. This patient's abdominal radiograph showed an inverted U-shaped shadow. The fasting breath CH(4) level was 26 ppm. An endoscopic procedure was immediately carried out with suspected sigmoid colon volvulus, and detorsion was achieved. There was resolution of the sigmoid volvulus after colonoscopy, and breath CH(4) concentration in the next morning decreased to 10 ppm. A liquid meal was supplied at noon on the second hospital day. The breath CH(4) concentration increased markedly to 38 ppm at 18:00 although she had no abdominal symptoms. This value peaked at 42 ppm at 18:00 on the third hospital day and was gradually reduced to 20 ppm the next day. The breath H(2) concentration value kept a low level during fasting and increased markedly to 51 ppm the next day after a liquid meal was supplied. The next morning, fasting breath H(2) concentration rapidly decreased to 6 ppm. This suggests that changes in breath H(2) levels may reflect transient malabsorption after a liquid test meal is supplied. In conclusion, breath H(2) and CH(4) analysis may be another tool for evaluating the intestinal circumstances.     

Starch malabsorption and breath gas excretion in healthy humans consuming low- and high-starch diets

Dietary starch delivery to the colon and excretion in stools and the ability of unabsorbed carbohydrates to promote hydrogen and methane release in breath were evaluated in 6 volunteers during two 8-day periods on starch diets of 100 and 300 g, respectively. Significantly less starch was recovered from the terminal ileum by aspiration per 24 h during the low-starch period (4.1 +/- 0.3 vs. 9.5 +/- 1.1 g, mean +/- SEM, p less than 0.01). Unabsorbed glucose tended to rise during the high-starch period (2.7 +/- 0.8 vs. 1.1 +/- 0.3 g). Fecal outputs of starch, glucose, volatile fatty acids, and lactic acid were not significantly different during the two periods. Daily breath hydrogen excretion was unchanged (181.2 +/- 22.7 vs. 193.7 +/- 19.8 ml for the low- and high-starch periods, respectively), whereas breath methane excretion increased markedly in the three methane producers during the high-starch period (217.2 +/- 80.9 vs. 32.4 +/- 7.3 ml). Starch malabsorption in the healthy small intestine was moderate even with a high-starch diet and less than that previously estimated by indirect methods. Unabsorbed starch catabolism by the colonic flora does not seem to explain most of the breath hydrogen excretion.     

Alteration of sulfate and hydrogen metabolism in the human colon by changing intestinal transit rate

OBJECTIVES: Changes in intestinal transit rate are also implicated in the etiology of many colonic diseases and strongly influence many metabolic processes in the colon. We set out to investigate whether intestinal transit time could influence the activity of the hydrogen-consuming bacterial flora and sulfate metabolism. METHODS: Normal volunteers underwent four interventions while taking a low-sulfate diet: placebo, sulfate supplements, or sulfate supplements with either senna or loperamide. Stools were cultured and analyzed for sulfate, sulfide, methionine, sulfate reduction rates, methionine reduction rates, acetic acid production rates, methane production rates, short-chain fatty acids, and bile acids. Urine was analyzed for sulfate. RESULTS: The addition of sulfate alone increased fecal and urinary excretion of sulfate, fecal sulfide, sulfate reduction rates, and acetic acid production rates; it reduced fecal methanogenic bacterial concentrations. Faster intestinal transit increased fecal sulfate, sulfide, bile acids, the reduction rates of sulfate, and methionine and the production rates of acetic acid. Reduction in fecal methanogens and methane production was seen. The reverse effects were seen with loperamide. CONCLUSIONS: Both sulfate supplements and changes in intestinal transit rate markedly alter the activity of the colonic bacterial flora with respect to sulfate metabolism and hydrogen disposal. Dietary influences on intestinal transit and sulfate consumption may influence disease processes. While a variety of processes govern sulfate metabolism and hydrogen disposal, our knowledge is far from complete. How far the observed changes in sulfate metabolism seen in certain diseases are relevant to the pathogenesis of the disease or secondary to the disease itself is unclear.     

Studies on breath methane: the effect of ethnic origins and lactulose.

The prevalence of methane production in an adult population of 256 subjects was 41%, but it was significantly higher in females (49%), than males (33%). When the population was subdivided into ethnic groups. Caucasians (48%) and Black (45%) had significantly more methane producers than Orientals (24%) and Indians (32%). when the ethnic groups were analysed by sex, female Caucasians had the highers prevalence (58%), significantly more than Caucasian males, Oriental males, and females and Indian males. In contrast with previous studies, a single dose of lactulose was found to significantly increase breath methane concentrations in six out of 12 methane producers, but not in 25 non-methane producers from the population study. In conclusion, any studies on breath methane must take into consideration the ethnic origin of the subjects and, contrary to previous advice, substrate intake, especially undigestible carbohydrates. Furthermore, a single breath sample may miss up to one-fifth of methane producers.     

Inhibition of methanogenesis by human bile.

The factors that regulate methanogenesis in humans have not been established. The presence of bile acid, which is lost into the colon from the small intestine, may be an important regulatory factor of methanogenesis. To examine this possibility, the effect of human bile on methane production by faecal cultures, and the in vivo effect of biliary diversion on breath methane excretion in a methanogenic choledochostomy patient, were investigated. Faecal suspensions (0.1%) from five methanogenic humans were incubated anaerobically with bile (0.3-30%) from three choledochostomy patients, and headspace methane measured by gas chromatography. All biles inhibited headspace methane. Inhibition of methanogenesis was dose dependent, plateaued at 10-30% bile concentration, and was abolished by 0.6% cholestyramine. The maximum inhibition by bile, median (range), was 38 (0.9-56)% of control methane values. Reversal of the bile fistula in the fourth choledochostomy patient converted that subject from methanogenic to 'non-methanogenic' status, It is concluded that inhibition of methanogens in the caecum by bile acid could significantly reduce the number of methanogens in the colon. This and the effect of transit time could explain much of the known epidemiology of 'non-methanogenesis', which has been related to obesity, (comparatively) fast colonic transit in healthy persons, and to small intestinal Crohn's disease.     

Fermentation of the Carbohydrate of Banana (Paradisiaca sapientum) in the Human Large Intestine.

Fermentation of dietary fiber and resistant starch is one of the major physiological functions of the human large intestine. The major substrate for fermentation is probably starch. This study assessed the effect of bananas—a carbohydrate with a highly resistant starch content—on breath hydrogen and methane production in methane and nonmethane-producing subjects. The results showed that both groups produced significant quantities of hydrogen after a banana meal, compared with a sucrose control test meal, measured as area under the curve (28 ± 5.6 vs. 8.1 ± 1.4 10³ pm/min, p = 0.008 in methane producers and 39 ± 15.2 vs. 10.5 ± 4.1 10³ ppm/min, p = 0.01 in methane nonproducers). The rise in breath hydrogen started a half hour after the banana meal and peaked at 31/2 h in methane nonproducers, whereas in methane producers, the rise began after 2 h and peaked at 5 h. Methane production was not significantly stimulated by the test meals. This study shows that bananas stimulate fermentation mainly through the production of hydrogen, with minimal effect on methane production. The possible mechanisms for this process are discussed.