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.     

Alterations of the colonic flora and their effect on the hydrogen breath test

The hydrogen breath test was performed by ingestion of 20 g lactulose and analysis of end-expiratory air. Eighteen patients undergoing colonoscopy, 17 receiving antibiotics, 12 prepared for colon surgery, and 15 controls were examined. The test was repeated under control conditions in the treated patients. Eleven of 55 subjects failed to produce significant amounts of hydrogen under control conditions. This 20% proportion of non-hydrogen producers is much higher than that reported by other investigators. The hydrogen production was very markedly depressed after preparation for colonscopy and antibiotic therapy. The effect of neomycin and enemata as used in preparation for colon surgery was less marked. Hydrogen production by the colonic flora is thus subject to individual variations and may be affected by various therapeutic regimens. All these may cause false negative results when using the hydrogen breath test to evaluate carbohydrate absorption. The test should therefore not be performed for a considerable time after therapeutic manipulation of the colonic flora.     

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.     

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.     

Breath hydrogen analysis in patients with ileoanal pouch anastomosis.

The possible influence on functional outcomes of hydrogen production in the ileoanal pouch after restorative proctocolectomy was investigated by means of lactulose H2 breath tests. Eight of 15 patients had significant increases in breath hydrogen after 10 g lactulose. One patient declined to participate in further investigations, the remaining seven responders had no evidence of small bowel bacterial overgrowth after glucose H2 breath tests. The ability to produce hydrogen by anaerobic fermentation of lactulose in the pouch was unrelated to the age of the patients or of the pouch. Seven of eight responders had successive breath tests after ingestion of lactulose 20 g and wheat starch 100 g. Five of seven had significant increases after lactulose but none after wheat starch. The overall function of the pouch continence, spontaneity of defecation, and 24 hour stool frequency was significantly better in responders than in non-responders. The absence of H2 production of 100 g wheat starch may indicate either increased absorption or defective fermentation.     

Assessment of lactose absorption by measurement of urinary galactose

Individuals with sufficient intestinal lactase hydrolyze ingested lactose to galactose and glucose and these monosaccharides are absorbed. Lactose is not digested completely when intestinal lactase activity is low and the disaccharide is malabsorbed. Breath hydrogen excretion after lactose ingestion is used commonly to diagnose lactose malabsorption. However, no direct tests are currently used to assess lactose absorption. We tested a new method of assessing lactose absorption in 26 healthy individuals. Each subject ingested 50 g of lactose. Participants were evaluated for lactose malabsorption using a standard 3-h breath hydrogen test. In addition, the urinary excretions of galactose, lactose, and creatinine were quantitated for 3-5 h after lactose ingestion. On the basis of breath hydrogen analysis after lactose ingestion, 12 individuals were lactose malabsorbers (defined as a rise in the breath hydrogen concentration of greater than 20 parts per million above the baseline value). The 14 subjects who did not malabsorb lactose by breath hydrogen testing (defined as a rise in the breath hydrogen concentration of less than or equal to 20 parts per million above the baseline value), had significantly more galactose in their urine 1, 2, and 3 h after lactose ingestion than lactose malabsorbers. The ratio of excreted lactose to excreted galactose was significantly decreased in lactose absorbers compared with lactose malabsorbers (p less than 0.001). Determination of the ratio of urinary galactose to urinary creatinine separated lactose absorbers from lactose malabsorbers completely (p less than 0.001). We conclude from this study that the determination of urinary galactose, urinary lactose/galactose ratio, and urinary galactose/creatinine ratio may be used to assess lactose digestion and absorption in healthy adults.     

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.     

Evaluation of the hydrogen breath test in man: definition and elimination of the early hydrogen peak.

After ingestion of a non-absorbable carbohydrate breath hydrogen excretion increases early at about 10 minutes, and again later when the ingested carbohydrate enters the caecum. The late rise has been used as a marker of mouth to caecum transit time, but the source of the early rise has not been satisfactorily explained. We studied in 60 healthy volunteers the source and frequency of the early rise in breath hydrogen after ingestion of a non-absorbable carbohydrate. After ingestion of either lactulose solution (10 g in 150 ml water), lentil soup (46 g carbohydrate) or solid meal containing baked beans (15 g carbohydrate), breath hydrogen was significantly raised above basal concentrations within 10 minutes (81 +/- 27, 395 +/- 138 and 110 +/- 52% above basal respectively). A significant rise in breath hydrogen (75 +/- 21%) occurred 10 minutes after sham lactulose feeding (lactulose applied to oral cavity but not swallowed), but no early peak occurred after sham saccharin feeding (non-fermentable carbohydrate), intragastric or intraduodenal administration of lactulose. Ten of the 12 subjects given lactulose sham feeding were restudied after oral hygiene with chlorhexidine mouthwash. In these the early hydrogen peak was abolished. Oral hygiene also reduced the occurrence and magnitude of the early hydrogen rise after lactulose ingestion. These findings indicate that the early rise in breath hydrogen observed after ingestion of lactulose is produced by interaction with oral bacteria.     

Breath testing to evaluate lactose intolerance in irritable bowel syndrome correlates with lactulose testing and may not reflect true lactose malabsorption

OBJECTIVES: An increased prevalence of lactose intolerance is seen in irritable bowel syndrome (IBS). Recently, we demonstrated a high prevalence of abnormal lactulose breath test results in IBS suggesting bacterial overgrowth. Because symptoms of lactose intolerance result from bacterial fermentation, the purpose of this study was to determine whether an abnormal lactose breath test is reflective of malabsorption or early presentation to bacteria. METHODS: Subjects with diarrhea-predominant IBS were enrolled. On day 1, subjects underwent a lactulose breath test after an overnight fast. Within 1 wk, subjects returned after fasting for a lactose breath test with simultaneous blood glucose measurements every 15 min to complete a lactose tolerance test (LTT). Symptoms were evaluated 3 h after lactose administration. RESULTS: Twenty subjects completed the study. One subject inadvertently received dextrose through the intravenous and was excluded. Of the remaining 19 subjects, three (16%) had an abnormal LTT suggesting malabsorption. In all, 10 subjects (53%) had an abnormal lactose breath test, 14 (74%) had an abnormal lactulose breath test, and 11 (58%) had symptoms after lactose administration. The agreement with symptoms was moderate (kappa = 0.47) and fair (kappa = 0.24) when compared to the lactose breath test and LTT, respectively. There was a fair correlation between lactose breath test and LTT (kappa = 0.29). However, lactose breath test hydrogen levels >166 ppm were universally predictive of abnormal LTT. Finally, a significant correlation was seen between the hydrogen production on lactose and lactulose breath test (r = 0.56, p = 0.01). CONCLUSIONS: Lactose breath testing in IBS subjects does not seem to reflect malabsorption; it may be an indicator of abnormal lactulose breath test, suggesting bacterial overgrowth.     

Breath hydrogen excretion after lactose and whole milk ingestion. A prospective comparison in lactase deficiency

As the 50 g of lactose in the usual clinical test is unphysiologic both because it is equivalent to 1 L milk and because the usual dietary intake is not the purified sugar, but milk, we undertook a prospective comparison of the absorption of lactose after both lactose and milk ingestion with an equivalent lactose content. We studied 51 healthy volunteers, using the hydrogen breath test technique. All patients received 25 g lactose in aqueous solution. Subjects with an abnormal test had the test repeated with 500 ml whole cow's milk, whereas subjects with a normal test repeated the test after ingesting the unabsorbable sugar lactulose to detect the capacity of their colonic flora to produce the gas. Symptoms of gastrointestinal intolerance were also recorded. Compared to an equivalent lactose amount, milk lactose is better absorbed (8% of the entire population malabsorbed 500 ml whole milk, whereas 33.33% malabsorbed 25 g lactose) and induces intolerance in fewer subjects. We conclude that milk rather than pure lactose must be used in clinical evaluation of lactose malabsorption and intolerance.     

Milk is a useful test meal for measurement of small bowel transit time

To improve and standardize the measurement of small bowel transit time, milk was employed for the test meal instead of the conventional lactulose meal. Although 92% of the subjects were lactase deficient, only 2% were milk intolerant and 13% were lactose intolerant. Small bowel transit time with milk (milk breath hydrogen test) was 113±9 min (mean ± SE,n=20); the normal range calculated from the mean ±2 SD was 31–195 min. The coefficient of variation in the milk hydrogen breath test was 13 ± 4% (n=6), whereas in the lactulose hydrogen breath test, it was 39±16% (n=10). The frequency of non-hydrogen producers, the occurrence of discomfort, and the reproducibility were better, though not significantly so, in the milk hydrogen breath test than in the lactulose. Since lactase activity in the intestine is variable in lactase-deficient subjects, small bowel transit times for milk may change from subject to subject. However, individual reproducibility of the milk hydrogen breath test is good. It could be useful for pharmacological experiments using paired comparison, for screening tests, or for the follow up of diseases in which small bowel transit time is affected.     

Deadaption and readaptation with lactose, but no cross-adaptation to lactulose: a case of occult colonic bacterial adaptation.

The standard 3 h breath hydrogen (3hBH2) test distinguishes lactose maldigesters from lactose digesters. However, multiple factors impact on BH2 and care is needed to exclude a priori variables. When these factors are controlled, a negative BH2 test implies lactase persistent status or lactase nonpersistent status with colonic adaptation. A case of a Sicilian man who tested negative (lactase persistent status confirmed) on an initial 50 g lactose challenge is described. It was observed that he consumed 28.1 g lactose/day before testing. He subsequently underwent five additional challenge tests in the course of the next 10 months. In four tests the dose intake of lactose was varied upon instruction, and in the fifth test a 30 g lactulose challenge was carried out. It was demonstrated that on radically decreasing lactose intake, a full lactase nonpersistent status was unmasked. Output of 3hBH2 varied inversely with daily lactose intake. Finally, at a time when he was readapted to lactose, there was no discernible adaptation to lactulose challenge. It was concluded that 'occult' colonically adapted subjects may contribute to negative BH2 tests. There is a relationship between variation in lactose intake and the results of BH2 testing. Finally, there was no cross-adaptation to lactulose challenge when lactose was used as the adapting sugar.     

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.     

Variations in colonic H2 and CO2 production as a cause of inadequate diagnosis of carbohydrate maldigestion in breath tests

BACKGROUND: Lactose maldigestion is usually diagnosed by means of the H2 breath test. When 13C-lactose is used as substrate, a 13CO2 breath test can be performed simultaneously. In an earlier publication we described the relation between both the H2 and 13CO2 exhalation in breath and the measured intestinal lactase activity after consumption of 13C-lactose. We found a discrepancy between both breath test results in 36% of the cases. To investigate the possible cause of these incongruous breath test results, we studied gas production from carbohydrate in the colon, using 13C-lactulose as a non-absorbable substrate. METHODS: Experiments were performed in 21 subjects, by applying 5 different doses of 13C-lactulose. Repeatability studies were performed in six of these subjects, using 10 g substrate (three tests with 1-week intervals). RESULTS: Both the H2 and the 13CO2 excretion in breath varied strongly interindividually and intraindividually after consumption of 13C-lactulose. In both cases no dose-response relation was observed. A significant positive linear relationship was found between H2 and 13CO exhalation (r = 0.45, P < 0.005). Extrapolation of these results to 13C-lactose breath tests indicates that the colonic contribution of 13CO2 production to the total 13CO2 excretion in breath varies but is on the average large enough to cause false-negative 13CO2 breath test results. CONCLUSIONS: Excretion in breath of 13CO2 produced in the colon during a 13C-lactulose breath test correlates with the breath H2 excretion. This could explain the occurrence of false-negative 13CO2 lactose breath tests when colonic gas production is high and false-negative lactose H2 breath test results when gas production is low. It can also explain the improved sensitivity of the combined H2/13CO2 lactose breath test compared with both breath tests alone.     

Comparison of abdominal bloating severity between irritable bowel syndrome patients with high and low levels of breath hydrogen excretion in a lactulose breath test

BackgroundThere is growing evidence that gut flora plays a role in the development of Irritable Bowel Syndrome (IBS). Abdominal bloating is a common symptom in these patients and the severity of this symptom could be related to the variations in their fermentative profiles, obtained by measuring the levels of breath hydrogen excretion after lactulose ingestion.AimsOur objective was to determine the difference in abdominal bloating severity between IBS patients with high vs low levels of breath hydrogen excretion after lactulose administration.MethodsLactulose breath tests were carried out on IBS patients in our institution between July 2009 and August 2010. Patients were requested to fill out a validated questionnaire to assess the severity of their symptoms. Abdominal bloating severity score was compared among patients with high and low breath hydrogen levels.ResultsA total of 234 patients were enrolled. There was a statistically significant difference in the abdominal bloating severity score between groups: 7.0 (5.7-8.0) vs 6.5 (5.0-7.5), p=0.001. The comparison among IBS patients with constipation (IBS-C) in both groups also showed a statistically significant difference: 7.5 (6.0-8.5) vs 5.8 (3.5-7.2), p=0.0051.ConclusionsThose patients with a low level of breath hydrogen excretion after lactulose ingestion presented with significantly greater abdominal bloating than those with a high level of breath hydrogen excretion.     

Hydrogen breath test as an indicator of the quality of colonic preparation for colonoscopy

BACKGROUND: Breath hydrogen levels after ingestion of polyethylene glycol were evaluated as a method of predicting the quality of colonic preparation. METHODS: One hundred patients undergoing nonemergency colonoscopy were recruited for this study. After fasting overnight, they were instructed to ingest a polyethylene glycol solution containing 12 g lactulose at a rate of 50 mL every 5 minutes for 2 hours. During ingestion of the polyethylene glycol solution, breath samples were taken at 15-minute intervals for 240 minutes and breath hydrogen concentration was measured. RESULTS: The preparation for colonoscopy was judged to be poor in 18% and adequate in 82%. The breath hydrogen levels over 90 minutes were significantly higher in the poor group than in the adequate group. In all patients with a breath hydrogen level less than 10 parts per million at 240 minutes, the preparation was adequate. Conversely, all patients with a poor preparation had a breath hydrogen level of more than 10 ppm at 240 minutes. CONCLUSIONS: The hydrogen breath test effectively predicts adequacy of colonic preparation.     

Early hydrogen excretion peaks during breath tests. Small intestinal bacterial overgrowth or accelerated transit?

BackgroundSmall intestinal bacterial overgrowth (SIBO) has been reported with varying prevalence, depending upon the criteria used for diagnosis. Lactulose and glucose breath tests are the most used in clinical settings. Early rises of hydrogen excretion during a lactose breath test suggest SIBO, but the finding could result from accelerated mouth-to-caecum transit time.AimsDefining the prevalence of early hydrogen peaks during lactose breath tests and assessing the proportion of patients affected by SIBO.MethodsAn early (≤ 60′) hydrogen excretion peak was observed in 120/663 patients with positive lactose hydrogen breath test. Eighty-one of them underwent a 50 g-9sample-glucose hydrogen breath test to diagnose SIBO.ResultsThe glucose breath test proved positive in 11/81 (13.6%) patients. The positivity rate was 18.2% (2/11) in those with the first peak detected at 30′ and 12.8% (9/70) in those with the peak occurring at 60′.ConclusionsEarly hydrogen excretion peaks are rarely associated with SIBO. The low positive predictive value indicates that the finding does not help identifying patients at high risk for this condition. Indirectly, the present data support the opinion that the prevalence of SIBO diagnosed by standard lactulose breath tests is much lower than reported, and the reliability of the test is low.     

Short duration exercise increases breath hydrogen excretion after lactulose ingestion: description of a new phenomenon

OBJECTIVE: There is limited information on the effect of exercise on colonic function. Beneficial effects have been described, including prevention of colon cancer. In the present study, we demonstrate that short duration exercise results in enhancement of breath hydrogen excretion after consumption of lactulose. METHODS: Twelve normal volunteers who performed regular exercise were recruited. Each study subject underwent four study sessions (two resting and two exercise) after consumption of 10 g of crystalline lactulose. Colonic hydrogen production was measured in mid-expiratory breath samples obtained at baseline and frequent intervals to 420 min. Exercise sessions consisted of 5 min on a treadmill at a 20% incline at 10 km/h. This was performed 180 min after lactulose ingestion in the two exercise sessions. RESULTS: A characteristic pattern in the hydrogen concentration versus time curves was seen after exercises, consisting of an initial decrease then an increase in concentration above baseline for up to 3 h. Mean area under the curve from 0 to 420 min for resting studies was 5,156 +/- 2,621 ppm/min and was 7,051 +/- 2,447 ppm/min for exercise studies, p < 0.05 (37% increase). Mean area under the curve from 180 to 420 min was 2,808 +/- 1,592 ppm/min for resting studies and 4,543 +/- 1,729 for exercise studies, p < 0.005 (62% increase). CONCLUSION: This study demonstrates that exercise potentially enhances the metabolism of lactulose by colonic bacteria. The authors postulate that this effect is due to stirring of the colonic contents. The described phenomenon may explain, in part, the beneficial effects of exercise on colonic mucosa.     

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.     

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.