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 inbreath H₂ excretion following prolongedingestion of malabsorbed carbohydrate (lactulose,lactose in lactose maldigesters) was studied in six lactose-maldigesting adults.Metabolic inhibitors of the three mainH₂-consuming reactions (methanogenesis,sulfate reduction, and acetogenesis) were used toindependently measure H production and consumption in fecal samples obtained after10 days of either dextrose or lactose feeding. Absolutefecal H₂ production (net of production minusconsumption) after 3 hr of incubation with lactose was approximately threefold lower after lactoseadaptation (242 ± 54 l) compared to dextroseadaptation (680 ± 79 l, P = 0.006). FecalH₂ consumption was not affected by eitherfeeding period. We conclude that decreased absolute H₂ production,rather than increased H₂ consumption, isresponsible for the decrease in breath H₂observed with lactose feeding.     

Prevalence and consistency of low breath H2 excretion following lactulose ingestion

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 12 g 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 12 g of lactulose increased their breath H₂ levels over 20 ppm when tested with 20 g. 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.     

Breath hydrogen and methane excretion produced by commercial beverages containing dietary fiber

Soft drinks containing dietary fiber are popular in Japan. There seem to be two types, one containing polydextrose and the other, oligosaccharide. These beverages are claimed to be useful for constipation or obesity, but data are scanty. We examined four such fiber-containing beverages [Fibe-mini Otsuka Pharmaceuticals (Tokyo, Japan), Seni and Oligo Takeda Food Engineering (Osaka, Japan), Oligo CC (Calpis Food Engineering, Tokyo, Japan), and Sapitus 5289 Nakakita Pharmaceuticals (Nagoga, Japan)] for large intestine fermentability by measuring breath hydrogen (H₂) and methane (CH₄). Five healthy subjects (two men, three women, 22–48 years old) participated in the study. Breath H₂ and CH₄ were measured with a MicroLyzer (Quintron Instruments, Milwaukee, Wis.). Breath H₂ increased within 2h of beverage consumption, but CH₄ excretion was observed in only two subjects. Orocecal transit time was constant for all beverages. Total H₂ plus CH₄ excretion (AUC; area under the curve) after lactulose was 1294±250ppm × min/g fiber. AUC for Oligo CC was significantly greater than that for Fibe-mini or Sapitus 5289 (P<0.05). The AUCs of Fibe-mini, Seni and Oligo, Oligo CC, and Sapitus 5289 were 41%, 129%, 174%, and 40%, respectively, that of lactulose. It is concluded that commercial fiber-containing drinks produce H₂, and CH₄ in some people. Oligosaccharide produces more H₂ and CH₄ than polydextrose.     

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.     

Usefulness of the double-balloon enteroscope in colonoscopies performed in patients with previously failed colonoscopy

Jejunal flora, bile acid deconjugation, and breath hydrogen (H₂) and methane (CH₄) excretion were studied in 22 Billroth II (BII)-operated patients with chronic postprandial symptoms, dumping (9), vomiting (7), pain (10), and diarrhoea (14). Sixteen were below 90% of desirable weight. Two control groups were included, one comprising 5 symptom-free, BII-operated volunteers and another comprising 12 healthy, unoperated volunteers. The numbers of bacteria recovered from jejunal secretions in the postgastrectomy patients did not differ significantly from those recovered in the symptom-free BII-operated controls but were significantly lower in the unoperated controls. Production of fermentation gas in anaerobic media supplemented with carbohydrates occurred in 17 of 22 postgastrectomy patients and in 4 of 5 BII-operated controls but in none of the unoperated controls. Bacterial bile acid decon-jugating activity did not differ significantly between the postgastrectomy patients and the BII-operated controls but was significantly lower in the unoperated controls. Breath H₂ excretion after glucose ingestion was significantly higher in the postgastrectomy patients than in both the BII-operated and the unoperated controls. The addition of pectin or guar gum to the glucose meal largely prevented postprandial symptoms and breath hydrogen excretion. Six out of 12 postgastrectomy patients treated with metronidazole recorded symptomatic effects, mainly on diarrhoea. Our findings indicate that jejunal bacterial overgrowth may be a major cause of the symptoms in some postgastrectomy patients. The tests available for demonstration of small-bowel bacterial overgrowth, perhaps with the exception of the glucose H₂ breath test, did not differentiate satisfactorily between symptom-producing and non-symptom-producing abnormal jejunal flora. Thus these tests may seem to have a limited practical diagnostic value in such patients.     

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 ¹³CO₂ exhalation (r = 0.45, P &lt; 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.     

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.     

Methane production and small intestinal bacterial overgrowth in children living in a slum

AIM:To analyze small intestinal bacterial overgrowth in school-aged children and the relationship between hydrogen and methane production in breath tests.METHODS:This transversal study included 85 children residing in a slum and 43 children from a private school,all aged between 6 and 10 years,in Osasco,Brazil.For characterization of the groups,data regarding the socioeconomic status and basic housing sanitary conditions were collected.Anthropometric data was obtained in children from both groups.All children completed the hydrogen(H 2) and methane(CH 4) breath test in order to assess small intestinal bacterial overgrowth(SIBO).SIBO was diagnosed when there was an increase in H 2 ≥ 20 ppm or CH 4 ≥ 10 ppm with regard to the fasting value until 60 min after lactulose ingestion.RESULTS:Children from the slum group had worse living conditions and lower nutritional indices than children from the private school.SIBO was found in 30.9%(26/84) of the children from the slum group and in 2.4%(1/41) from the private school group(P = 0.0007).Greater hydrogen production in the small intestine was observed in children from the slum group when compared to children from the private school(P = 0.007).A higher concentration of hydrogen in the small intestine(P 0.001) and in the colon(P 0.001) was observed among the children from the slum group with SIBO when compared to children from the slum group without SIBO.Methane production was observed in 63.1%(53/84) of the children from the slum group and in 19.5%(8/41) of the children from the private school group(P 0.0001).Methane production was observed in 38/58(65.5%) of the children without SIBO and in 15/26(57.7%) of the children with SIBO from the slum.Colonic production of hydrogen was lower in methaneproducing children(P = 0.017).CONCLUSION:Children who live in inadequate environmental conditions are at risk of bacterial overgrowth and methane production.Hydrogen is a substrate for methane production in the colon.     

Applicability of short hydrogen breath test for screening of lactose malabsorption

The gold standard for diagnosing lactose malabsorption is the H₂ hydrogen breath test (HBT). Different methods of HBT have been proposed. However, in clinical practice the HBT is often shortened to 1–2 hr without proper validation. Our objective was to establish whether the usefulness of the HBT is influenced by shortening of the test and/or by substrate variations. In 62 patients with clinically suspected lactose intolerance and a positive lactose HBT we calculated the sensitivity of the HBT depending on the duration of the HBT. To determine whether substrate variations influence the sensitivity of the HBT, in another group of 32 patients with clinically suspected lactose intolerance and a positive milk HBT, the sensitivity of the HBT was also calculated depending on the duration of the test after milk ingestion. In other unselected 97 individuals, the result of the HBT with 360 ml of whole milk supplemented with lactose was compared with a symptomatic score for lactose intolerance to evaluate the specificity of the shortened milk HBT. Breath H₂ excretion was significantly higher after lactose than after milk load (P < 0.01), and the increase in H₂ appeared earlier with lactose than with milk (60 vs 90, min respectively). HBT duration influenced the sensitivity of the test that decreased from 95% for the 3-hr HBT to 37% for the 1-hr HBT with lactose and from 80% for 3-hr HBT to 21% for 1-hr HBT with milk. The specificity was similar for the 3-hr milk HBT and the 5-hr test (67 vs 62%). In conclusion, for screening of lactose malabsorption, the HBT can be shortened to 3 hr without loss of sensitivity and specificity, when a high dose of lactose load is used.     

Hydrogen- and Methane-Based Breath Testing and Outcomes in Patients With Heart Failure

BackgroundRecent evidence endorses gut microbiota dysregulation in the pathophysiology of heart failure (HF). Small intestinal bacterial overgrowth (SIBO) might be present in HF and associated with poor clinical outcomes. Lactulose breath testing is a simple noninvasive test that has been advocated as a reliable indicator of SIBO. In patients with HF, we aimed to evaluate the association with clinical outcomes of the exhaled hydrogen (H₂) and methane (CH₄) concentrations through the lactulose breath test.Methods and ResultsWe included 102 patients with HF in which lactulose SIBO breath tests were assessed. Cumulative gas was quantified by the area under the receiver operating characteristic curve of CH₄ (AUC-CH₄) and H₂ (AUC-H₂). Clinical end points included the composite of all-cause death with either all-cause or HF hospitalizations, recurrent all-cause hospitalizations, and recurrent HF hospitalizations. Medians (interquartile ranges) of AUC-H₂ and AUC-CH₄ were 1290 U (520-2430) and 985 U (450-2120), respectively. In multivariable analysis, AUC-H₂ (per 1000 U) was associated with all-cause death/all-cause hospitalization (hazard ratio [HR] 1.21, 95% CI 1.04–1.40; P = .012), all-cause death/HF hospitalization (HR 1.20, 95% CI 1.03–1.40; P = .021), and an increase in the rate of recurrent all-cause (incidence rate ratio [IRR] 1.31, 95% CI 1.14–1.51; P < .001) and HF (IRR 1.41, 95% CI 1.15–1.72; P = .001) hospitalizations. AUC-CH₄ was not associated with any of these end points.ConclusionsAUC-H₂, a safe and noninvasive method for SIBO estimation, is associated with higher risk of long-term adverse clinical events in patients with HF. In contrast, AUC-CH₄ did not show any prognostic value.     

Effects of age on lactose malabsorption in Oklahoma Native Americans as determined by breath H2 analysis

Breath H₂ excretion was used to determine lactose malabsorption in 30 healthy females and 30 healthy males between the ages of 3 and 64 yr who were at least 7/8 Native American. The test meal consisted of 5 ml reconstituted nonfat dry milk (0.25 g lactose) per kg of body weight. On the basis of breath H₂ tests in 15 control subjects with normal oral lactose tolerance tests, a response factor of 20 ppm was selected as the upper limit for lactose absorbers. Of the 60 subjects in the study group, 36 (60%) were classified as lactose malabsorbers since they had a response factor of 20 ppm or greater of breath H₂. Only 3 of 20 children (15%) who were under the age of 12 yr were nondigesters of the small lactose dose used in this study. Approximately 82 percent (82.5%) of subjects who were 13 yr and older were lactose malabsorbers. Adolescence appears to be the period in which malabsorption of lactose becomes evident in Native North Americans.Supported by the Nutrition Foundation, Inc., New York, New York; Biomedical Sciences Support Grant (USPH) 5-S05-RR7077 to The Research Foundation, Oklahoma State University.     

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.     

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.     

All Lactase Preparations Are Not the Same: Results of a Prospective, Randomized, Placebo-Controlled Trial

Objective: To compare the efficacy of three commercially available oral lactase preparations in adults with lactose intolerance. Methods: Design—Prospective, randomized, placebo-controlled trial. Setting—Outpatient study in a General Clinical Research Center. Subjects—Ten lactose-intolerant healthy volunteers were challenged with ice cream containing 18 g of lactose. Lactase or placebo was given immediately prior to challenge. Measurements—Symptoms and breath hydrogen excretion were recorded for 3 h following lactose challenge. Results: The three products differed in their abilities to influence symptoms and breath hydrogen excretion. Only Lactaid reduced the breath hydrogen excretion with lactose (mean peak, area under the curve and cumulative breath hydrogen excretion) ( P < 0.05). Lactrase and Dairy Ease influenced symptoms: Lactrase reduced pain, bloating and total symptomatic scores ( P < 0.05), whereas Dairy Ease only reduced pain ( P < 0.05). Lactaid administration did not reduce symptoms. Conclusion: In lactose-intolerant subjects, the available lactase preparations differ in their ability to improve both breath hydrogen excretion and symptoms. Lactrase may be the product of choice for achieving symptomatic improvement.     

Lack of effect of lactose digestion status on baseline fecal microflora

BACKGROUND:

The genetics of intestinal lactase divide the world’s population into two phenotypes: the ability (a dominant trait) or inability (a recessive trait) to digest lactose. A prebiotic effect of lactose may impact the colonic flora of these phenotypes differently.

OBJECTIVE:

To detect and evaluate the effects of lactose on subjects divided according to their ability to digest lactose.

METHODS:

A total of 57 healthy maldigesters (n=30) and digesters (n=27) completed diet questionnaires, genetic and breath hydrogen testing, and quantitative stool analysis for species of bacteria. Log₁₀ transformation of bacterial counts was compared with lactose intake in both groups using multiple regression analysis.

RESULTS:

There was a significant relationship between genetic and breath hydrogen tests. Daily lactose intake was marginally lower in lactose maldigesters (median [interquartile range] 12.2 g [31 g] versus 15 g [29.6 g], respectively). There was no relationship between lactose intake and breath hydrogen tests in either group. There were no differences in bacterial counts between the two groups, nor was there a relationship between bacterial counts and lactose intake in either group.

CONCLUSION:

The differential bacterial effects of lactose were not quantitatively detected in stool samples taken in the present study.     

Potential usefulness of hydrogen breath test withd-xylose in clinical management of intestinal malabsorption

Hydrogen breath tests (H₂ BT) have been used extensively to investigate intestinal dissacharidase deficiencies. A potentially useful test for assessing intestinal absorptive function, the H₂ BT withd-xylose (H₂ BT-d-xylose), has received scant attention. We report here the results of our investigation of this test in 45 patients. Fifteen patients had proved malabsorption that was due to nontropical sprue in nine, and to lymphoma, Whipple's disease, or giardiasis in the remainder. Nine patients had small-bowel bacterial overgrowth secondary to either postsurgical sequelae or intestinal dysmotility. Twenty-one patients with irritable bowel syndrome and 21 healthy individuals served as control groups. All participants ingested 25 g ofd-xylose, and alveolar breath samples were obtained thereafter at 30 min intervals for 5 hr. Breath H₂ was measured by chromatography. Basal H₂ production, peak change (Δ) and area under the curve (AUC) were calculated. Simultaneously, 5-hr urinary excretion ofd-xylose was measured by colorimetry and served as the reference test. In healthy individuals,d-xylose ingestion increased H₂ production (Δ=5.8±1.4 ppm,P<0.001). Changes were similar in patients with the irritable bowel syndrome. In contrast, the increase was of a much greater magnitude in the malabsorption group (Δ=49.9±7.2 ppm,P<0.001 vs healthy controls). AUC analysis yielded comparable results. Test performance analysis showed that, in malabsorption the H₂ BT-d-xylose had a sensitivity index of 0.86, which was identical to that of the urinaryd-xylose test. Specificity was 1 and 0.95, respectively; and predictability 1 and 0.93, respectively. All patients who responded to treatment normalized their H₂ production, whereas those who did not respond maintained their high H₂ production. In the bacterial-overgrowth group, the H₂ BT-d-xylose was only positive when the urinary excretion ofd-xylose was positive (five patients), whereas that three of the remaining four patients with normal urinary excretion ofd-xylose also had a normal breath test. We conclude that the hydrogen breath test withd-xylose is a useful, valid, and practical test for the diagnosis and follow-up of malabsorption.     

Lactase deficiency in Singapore-born and Canadian-born Chinese

Seventy-three of 77 adult Singapore-born Chinese (95%) and 48 of 49 Canadian-born adult Chinese (98%) were demonstrated to be lactase deficient using the lactose breath hydrogen test. The similar prevalence of lactase deficiency in the Singapore- and the Canadian-born Chinese despite a larger estimated amount of daily milk ingestion in the Canadian-born Chinese (430 ml vs 157 ml) supports the concept that lactase deficiency, which is transmitted genetically, does not have an adaptable component related to the quantity of lactose ingested. When the lactose breath hydrogen test performed with a dose of 0.5 g/kg of lactose was compared with the test using a standard dose of 50 g of lactose, there was very little loss of sensitivity. In spite of the presence of lactase deficiency, only 32% of the Singapore subjects and 23% of the Canadian subjects had gastrointestinal symptoms when milk was ingested in the daily diet. Peak breath H₂ was higher in females than males, but the difference was more significant in the Canadian cohort.     

Differential impact of lactose/lactase phenotype on colonic microflora

BACKGROUND:

The ability to digest lactose divides the world’s population into two phenotypes that may be risk variability markers for several diseases. Prebiotic effects likely favour lactose maldigesters who experience lactose spilling into their colon.

OBJECTIVE:

To evaluate the effects of fixed-dose lactose solutions on fecal bifidobacteria and lactobacilli in digesters and maldigesters, and to determine whether the concept of a difference in ability to digest lactose is supported.

METHODS:

A four-week study was performed in 23 lactose mal-digesters and 18 digesters. Following two weeks of dairy food withdrawal, subjects ingested 25 g of lactose twice a day for two weeks. Stool bifidobacteria and lactobacilli counts pre- and postintervention were measured as the primary outcome. For secondary outcomes, total anaerobes, Enterobacteriaceae, beta-galactosidase and N-acetyl-beta-D-glucosaminidase activity in stool, as well as breath hydrogen and symptoms following lactose challenge tests, were measured.

RESULTS:

Lactose maldigesters had a mean change difference (0.72 log₁₀ colony forming units/g stool; P=0.04) in bifidobacteria counts compared with lactose digesters. Lactobacilli counts were increased, but not significantly. Nevertheless, reduced breath hydrogen after lactose ingestion correlated with lactobacilli (r=−0.5; P<0.001). Reduced total breath hydrogen and symptom scores together, with a rise in fecal enzymes after intervention, were appropriate, but not significant.

CONCLUSIONS:

Despite failure to achieve full colonic adaptation, the present study provided evidence for a differential impact of lactose on microflora depending on genetic lactase status. A prebiotic effect was evident in lactose maldigesters but not in lactose digesters. This may play a role in modifying the mechanisms of certain disease risks related to dairy food consumption between the two phenotypes.     

Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces

Molecular hydrogen (H₂) is derived from the hydrothermal alteration of olivine-rich planetary crust. Abiotic and biotic processes consume H₂ to produce methane (CH₄); however, the extent of either process is unknown. Here, we assess the temporal dependence and limit of abiotic CH₄ related to the presence and formation of mineral catalysts during olivine hydrolysis (i.e., serpentinization) at 200 °C and 0.03 gigapascal. Results indicate that the rate of CH₄ production increases to a maximum value related to magnetite catalyzation. By identifying the dynamics of CH₄ production, we kinetically model how the H₂ to CH₄ ratio may be used to assess the origin of CH₄ in deep subsurface serpentinization systems on Earth and Mars. Based on our model and available field data, low H₂/CH₄ ratios (less than approximately 40) indicate that life is likely present and active.     

Gas and the Microbiome

Humans are host to trillions of microbial colonizers that contribute significantly to human health and disease. Advances in sequencing and other technologies have facilitated dramatic advances in our knowledge of the types and number of organisms colonizing different areas of the body, and while our knowledge of the roles played by the different bacteria, fungi, and archaea has increased dramatically, there remains much to uncover. The microbes that colonize the human gut contribute to vitamin biosynthesis, immune modulation, and the breakdown of otherwise indigestible foods for nutrient harvest. Bacteria and archaea produce various gases as by-products of fermentation, and it is becoming increasingly understood that these gases have both direct and indirect effects on the gut, and may also be used as diagnostic markers, e.g., hydrogen production as measured by breath testing can be used to diagnose bacterial overgrowth. In this article, we review the roles and effects of hydrogen (H₂), methane (CH₄) and hydrogen sulfide (H₂S) in the human gut.