Metabolic effects of eradicating breath methane using antibiotics in prediabetic subjects with obesity

Variations in the Relative Abundance of Gut Bacteria Correlate with Lipid Profiles in Healthy Adults

The gut microbiome is a versatile system regulating numerous aspects of host metabolism. Among other traits, variations in the composition of gut microbial communities are related to blood lipid patterns and hyperlipidaemia, yet inconsistent association patterns exist. This study aims to assess the relationships between the composition of the gut microbiome and variations in lipid profiles among healthy adults. This study used data and samples from 23 adult participants of a previously conducted dietary intervention study. Circulating lipid measurements and whole-metagenome sequences of the gut microbiome were derived from 180 blood and faecal samples collected from eight visits distributed across an 11-week study. Lipid-related variables explained approximately 4.5% of the variation in gut microbiome compositions, with higher effects observed for total cholesterol and high-density lipoproteins. Species from the genera Odoribacter, Anaerostipes, and Parabacteroides correlated with increased serum lipid levels, whereas probiotic species like Akkermansia muciniphila were more abundant among participants with healthier blood lipid profiles. An inverse correlation with serum cholesterol was also observed for Massilistercora timonensis, a player in regulating lipid turnover. The observed correlation patterns add to the growing evidence supporting the role of the gut microbiome as an essential regulator of host lipid metabolism.

Vitamin K2 supplementation improves impaired glycemic homeostasis and insulin sensitivity for type 2 diabetes through gut microbiome and fecal metabolites

BACKGROUND

There is insufficient evidence for the ability of vitamin K2 to improve type 2 diabetes mellitus symptoms by regulating gut microbial composition. Herein, we aimed to demonstrate the key role of the gut microbiota in the improvement of impaired glycemic homeostasis and insulin sensitivity by vitamin K2 intervention.

METHODS

We first performed a 6-month RCT on 60 T2DM participants with or without MK-7 (a natural form of vitamin K2) intervention. In addition, we conducted a transplantation of the MK-7-regulated microbiota in diet-induced obesity mice for 4 weeks. 16S rRNA sequencing, fecal metabolomics, and transcriptomics in both study phases were used to clarify the potential mechanism.

RESULTS

After MK-7 intervention, we observed notable 13.4%, 28.3%, and 7.4% reductions in fasting serum glucose (P = 0.048), insulin (P = 0.005), and HbA1c levels (P = 0.019) in type 2 diabetes participants and significant glucose tolerance improvement in diet-induced obesity mice (P = 0.005). Moreover, increased concentrations of secondary bile acids (lithocholic and taurodeoxycholic acid) and short-chain fatty acids (acetic acid, butyric acid, and valeric acid) were found in human and mouse feces accompanied by an increased abundance of the genera that are responsible for the biosynthesis of these metabolites. Finally, we found that 4 weeks of fecal microbiota transplantation significantly improved glucose tolerance in diet-induced obesity mice by activating colon bile acid receptors, improving host immune-inflammatory responses, and increasing circulating GLP-1 concentrations.

CONCLUSIONS

Our gut-derived findings provide evidence for a regulatory role of vitamin K2 on glycemic homeostasis, which may further facilitate the clinical implementation of vitamin K2 intervention for diabetes management.

TRIAL REGISTRATION

The study was registered at https://www.chictr.org.cn (ChiCTR1800019663).

Dysbiome and Its Role in Surgically Relevant Medical Disease

Several surgically relevant conditions are directly or indirectly influenced by the human microbiome. Different microbiomes may be found within, or along, specific organs and intra-organ variation is common. Such variations include those found along the course of the gastrointestinal tract as well as those on different regions of the skin. A variety of physiologic stressors and care interventions may derange the native microbiome. A deranged microbiome is termed a dysbiome and is characterized by decreased diversity and an increase in the proportion of potentially pathogenic organisms; the elaboration of virulence factors coupled with clinical consequences defines a pathobiome. Specific conditions such as Clostridium difficile colitis, inflammatory bowel disease, obesity, and diabetes mellitus are tightly linked to a dysbiome or pathobiome. Additionally, massive transfusion after injury appears to derange the gastrointestinal microbiome as well. This review explores what is known about these surgically relevant clinical conditions to chart how non-surgical interventions may support surgical undertakings or potentially reduce the need for operation.

Antibiotics administration alleviates the high fat diet-induced obesity through altering the lipid metabolism in young mice

Currently, there is a global trend of rapid increase in obesity, especially among adolescents. The antibiotics cocktails (ABX) therapy is commonly used as an adjunctive treatment for gut microbiota related diseases, including obesity. However, the effects of broad-spectrum antibiotics alone on young obese hosts have rarely been reported. In the present study, the 3-week-old C57BL/6J male mice fed a high-fat diet (HFD) were intragastric administration with ampicillin, vancomycin, metronidazole or neomycin for 30 days. The lipid metabolites in plasma were assessed by biochemical assay kits, and genes related to lipid metabolite in the white adipose were assessed by qPCR. To further analyze the underlying mechanisms, the expression of genes related to lipid metabolism, inflammatory reactions and oxidative stress in the liver were determined by qPCR assay. In addition, the expression of oxidative damage-associated proteins in the liver were detected by western blot. The results showed that oral antibiotics exposure could reduce body weight and fat index in HFD-fed mice, concurrent with the increase of white adipose lipolysis genes and the decrease of hepatic lipogenic genes. Furthermore, antibiotics treatment could clearly reverse the HFD-induced elevation of oxidative damage-related proteins in the liver. Together, these findings will provide valuable clues into the effects of antibiotics on obesity.

Mobile genetic elements from the maternal microbiome shape infant gut microbial assembly and metabolism

The perinatal period represents a critical window for cognitive and immune system development, promoted by maternal and infant gut microbiomes and their metabolites. Here, we tracked the co-development of microbiomes and metabolomes from late pregnancy to 1 year of age using longitudinal multi-omics data from a cohort of 70 mother-infant dyads. We discovered large-scale mother-to-infant interspecies transfer of mobile genetic elements, frequently involving genes associated with diet-related adaptations. Infant gut metabolomes were less diverse than maternal but featured hundreds of unique metabolites and microbe-metabolite associations not detected in mothers. Metabolomes and serum cytokine signatures of infants who received regular-but not extensively hydrolyzed-formula were distinct from those of exclusively breastfed infants. Taken together, our integrative analysis expands the concept of vertical transmission of the gut microbiome and provides original insights into the development of maternal and infant microbiomes and metabolomes during late pregnancy and early life.

Archaea from the gut microbiota of humans: Could be linked to chronic diseases?

Archaea comprise a unique domain of organisms with distinct biochemical and genetic differences from bacteria. Methane-forming archaea, methanogens, constitute the predominant group of archaea in the human gut microbiota, with Methanobrevibacter smithii being the most prevalent. However, the effect of methanogenic archaea and their methane production on chronic disease remains controversial. As perturbation of the microbiota is a feature of chronic conditions, such as cardiovascular disease, neurodegenerative diseases and chronic kidney disease, assessing the influence of archaea could provide a new clue to mitigating adverse effects associated with dysbiosis. In this review, we will discuss the putative role of archaea in the gut microbiota in humans and the possible link to chronic diseases.

Methanogen Abundance Thresholds Capable of Differentiating In Vitro Methane Production in Human Stool Samples

BACKGROUND

Intestinal methane (CH₄) gas production has been associated with a number of clinical conditions and may have important metabolic and physiological effects.

AIMS

In this study, taxonomic and functional gene analyses and in vitro CH₄ gas measurements were used to determine if molecular markers can potentially serve as clinical tests for colonic CH₄ production.

METHODS

We performed a cross-sectional study involving full stool samples collected from 33 healthy individuals. In vitro CH₄ gas measurements were obtained after 2-h incubation of stool samples and used to characterize samples as CH₄ positive (CH₄+) and CH₄ negative (CH₄-; n = 10 and 23, respectively). Next, we characterized the fecal microbiota through high-throughput DNA sequencing with a particular emphasis on archaeal phylum Euryarchaeota. Finally, qPCR analyses, targeting the mcrA gene, were done to determine the ability to differentiate CH₄+ versus CH₄- samples and to delineate major methanogen species associated with CH₄ production.

RESULTS

Methanobrevibacter was found to be the most abundant methane producer and its relative abundance provides a clear distinction between CH₄+ versus CH₄- samples. Its sequencing-based relative abundance detection threshold for CH₄ production was calculated to be 0.097%. The qPCR-based detection threshold separating CH₄+ versus CH₄- samples, based on mcrA gene copies, was 5.2 × 10⁵ copies/g.

CONCLUSION

Given the decreased time-burden placed on patients, a qPCR-based test on a fecal sample can become a valuable tool in clinical assessment of CH₄ producing status.

iNetModels 2.0: an interactive visualization and database of multi-omics data

It is essential to reveal the associations between various omics data for a comprehensive understanding of the altered biological process in human wellness and disease. To date, very few studies have focused on collecting and exhibiting multi-omics associations in a single database. Here, we present iNetModels, an interactive database and visualization platform of Multi-Omics Biological Networks (MOBNs). This platform describes the associations between the clinical chemistry, anthropometric parameters, plasma proteomics, plasma metabolomics, as well as metagenomics for oral and gut microbiome obtained from the same individuals. Moreover, iNetModels includes tissue- and cancer-specific Gene Co-expression Networks (GCNs) for exploring the connections between the specific genes. This platform allows the user to interactively explore a single feature's association with other omics data and customize its particular context (e.g. male/female specific). The users can also register their data for sharing and visualization of the MOBNs and GCNs. Moreover, iNetModels allows users who do not have a bioinformatics background to facilitate human wellness and disease research. iNetModels can be accessed freely at https://inetmodels.com without any limitation.

The Fecal Microbiota Is Already Altered in Normoglycemic Individuals Who Go on to Have Type 2 Diabetes

Objective

Mounting evidence has suggested a link between gut microbiome characteristics and type 2 diabetes (T2D). To determine whether these alterations occur before the impairment of glucose regulation, we characterize gut microbiota in normoglycemic individuals who go on to develop T2D.

Methods

We designed a nested case-control study, and enrolled individuals with a similar living environment. A total of 341 normoglycemic individuals were followed for 4 years, including 30 who developed T2D, 33 who developed prediabetes, and their matched controls. Fecal samples (developed T2D, developed prediabetes and controls: n=30, 33, and 63, respectively) collected at baseline underwent metagenomics sequencing.

Results

Compared with matched controls, individuals who went on to develop T2D had lower abundances of Bifidobacterium longum, Coprobacillus unclassified, and Veillonella dispar and higher abundances of Roseburia hominis, Porphyromonas bennonis, and Paraprevotella unclassified. The abundance of Bifidobacterium longum was negatively correlated with follow-up blood glucose levels. Moreover, the microbial Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of carbohydrate metabolism, methane metabolism, amino acid metabolism, fatty acid metabolism, and membrane transport were changed between the two groups.

Conclusions

We found that fecal microbiota of healthy individuals who go on to develop T2D had already changed when they still were normoglycemic. These alterations of fecal microbiota might provide insights into the development of T2D and a new perspective for identifying individuals at risk of developing T2D.

High intestinal hydrogen production in runners after intake of fructose solution

Fructose intake is associated with increased consumption of processed foods, specifically in the context of nutritional supplements. To assess gastrointestinal symptoms and hydrogen production after the ingestion of a fructose solution in runners, healthy and sick persons. Hydrogen test (H2 test) was performed after the intake a solution with 50 g fructose along with the application of a questionnaire to evaluate the gastrointestinal symptoms during the H2 test in three groups: Athletes group (AG); control group (CG) with healthy subjects; and non-alcoholic fatty liver disease group (NAFLDG). Statistical analysis was performed with analysis of variance at a p < 0.05 significance level. The AG was the largest H₂ producer followed by the CG with significant difference between the AG and NAFLDG (p ≤ 0.05). Most participants remained asymptomatic, but the strongest correlation was the symptom of bloating GC (R = 0.625), eructation in NAFLD (R = 0.481) and diarrhea in CG (R = 0.345) and AG (R = 0.338) The result of the present study suggests the production of hydrogen by the colon following the administration of fructose is higher in athletes compared with healthy individuals and persons with NAFLD, showing that fructose intake may be an interesting point of dietary management, especially in elite professionals.

Association between increased breath hydrogen methane concentration and prevalence of glucose intolerance in acute pancreatitis

Pancreatic damage, in the form of pancreatitis, intestinal bacteria and glucose imbalance could be interrelated. The aim of this study was to investigate the breath hydrogen (H₂) and methane (CH₄), which can indicate small intestinal bacterial overgrowth (SIBO) status, and assess the link between SIBO and glucose tolerance in patients with acute pancreatitis (AP). This prospective study enrolled 75 patients who were admitted for AP. A glucose breath test (GBT) which detects breath hydrogen H₂ and CH₄ for SIBO with an oral glucose tolerance test (OGTT) for 120 min was simultaneously performed to determine SIBO and glucose tolerance. Patient demographic data, laboratory test data, and computed tomography severity index (CTSI) were also evaluated. The levels of total breath H₂ and CH₄ in patients with AP were significantly higher than those in controls, respectively (p < 0.01). There were no significant differences in the incidence of SIBO between patients with AP and controls. The OGTT indicated that blood glucose levels at 30, 60, 90, and 120 min were higher in SIBO-positive patients than in SIBO-negative patients. No significant differences in CTSI, patient demographic data or laboratory test data were observed between the two groups. Breath H₂ and CH₄ concentrations are relatively higher in patients with AP, indicating a correlation between high levels of intestinal bacteria and AP. Furthermore, higher breath H₂ and CH₄ concentrations appear to be associated with oral glucose intolerance, with hyperglycemia occurring in patients with AP.

Exercise and Asthma

Asthma is a chronic lower respiratory disease that is very common worldwide, and its incidence is increasing year by year. Since the 1970s, asthma has become widespread, with approximately 300 million people affected worldwide and about 250,000 people have lost their lives. Asthma seriously affects people's physical and mental health, resulting in reduced learning efficiency, limited physical activities, and decreased quality of life. Therefore, raising awareness of the risk of asthma and how to effectively treat asthma have become important targets for the prevention and management of asthma in recent years. For patients with asthma, exercise training is a widely accepted adjunct to drug-based and non-pharmacological treatment. It has been recommended abroad that exercise prescriptions are an important part of asthma management.

Alzheimer's disease might depend on enabling pathogens which do not necessarily cross the blood-brain barrier

The development of Alzheimer's Disease (AD) might reflect, in its acquired aspects, a cooperative pathogenesis whereby infectious enablers which do not necessarily cross the blood-brain barrier augment the invasive properties of a less virulent organism, thus enabling it to infect the brain. An example interaction is described which involves Chlamydia species, Human papillomavirus (HPV), microbiota, and yeast, where yeast is a pathogen of low virulence which crosses the blood-brain barrier. The cooperative pathogenesis begins at the mucosal epithelium. Infection by Chlamydia, HPV, or dysbiosis of commensal bacteria disrupts the integrity of the mucosal epithelium, thereby allowing colonizing yeast to penetrate the epithelial barrier and enter into the bloodstream. Chlamydia and enabling commensals promote insulin resistance, which provides yeast with glucose and also sets the stage for accumulation of amyloid beta protein (ABP). Meanwhile, HPV-induced and hyperglycemia-induced immunological changes enable the spread of newly invasive yeast to the brain, where the release of inflammatory cytokines in response to yeast promotes production of ABP. Chlamydia also cross reacts with Candida species, which may stimulate further brain inflammation in response to Candida and may augment production of ABP thereby The yeast's less virulent origins, coupled with immune modulation by enablers, might explain why AD as a model of infectious encephalitis is always slow and insidious rather than occasionally febrile, accompanied by seizures, or marked by signs of meningeal inflammation.

Second-generation antipsychotics and metabolism alterations: a systematic review of the role of the gut microbiome

RATIONALE

Multiple drugs are known to induce metabolic malfunctions, among them second-generation antipsychotics (SGAs). The pathogenesis of such adverse effects is of multifactorial origin.

OBJECTIVES

We investigated whether SGAs drive dysbiosis, assessed whether gut microbiota alterations affect body weight and metabolic outcomes, and looked for the possible mechanism of metabolic disturbances secondary to SGA treatment in animal and human studies.

METHODS

A systematic literature search (PubMed/Medline/Embase/ClinicalTrials.gov/PsychInfo) was conducted from database inception until 03 July 2018 for studies that reported the microbiome and weight alterations in SGA-treated subjects.

RESULTS

Seven articles reporting studies in mice (experiments = 8) and rats (experiments = 3) were included. Olanzapine was used in five and risperidone in six experiments. Only three articles (experiments = 4) in humans fit our criteria of using risperidone and mixed SGAs. The results confirmed microbiome alterations directly (rodent experiments = 5, human experiments = 4) or indirectly (rodent experiments = 4) with predominantly increased Firmicutes abundance relative to Bacteroidetes, as well as weight gain in rodents (experiments = 8) and humans (experiments = 4). Additionally, olanzapine administration was found to induce both metabolic alterations (adiposity, lipogenesis, plasma free fatty acid, and acetate levels increase) (experiments = 3) and inflammation (experiments = 2) in rodents, whereas risperidone suppressed the resting metabolic rate in rodents (experiments = 5) and elevated fasting blood glucose, triglycerides, LDL, hs-CRP, antioxidant superoxide dismutase, and HOMA-IR in humans (experiment = 1). One rodent study suggested a gender-dependent effect of dysbiosis on body weight.

CONCLUSIONS

Antipsychotic treatment-related microbiome alterations potentially result in body weight gain and metabolic disturbances. Inflammation and resting metabolic rate suppression seem to play crucial roles in the development of metabolic disorders.

Obesity, diabetes, and the gut microbiome: an updated review

Obesity and diabetes are two of the most prevalent health problems and leading causes of death globally. As research on the intestinal microbiome increases, so does our understanding of its intricate relationship to these diseases, although this has yet to be fully elucidated. Areas covered: This review evaluates the role of the gut microbiome in obesity and diabetes, including the influences of internal and environmental factors. Literature searches were performed using the keywords 'diabetes,' 'insulin resistance,' 'gut microbiome,' 'gut microbes,' 'obesity,' and 'weight gain.' Expert commentary: Highlights of recent research include new findings regarding the effects of caloric restriction, which expound the importance of diet in shaping the gut microbiome, and studies reinforcing the lasting implications of antibiotic use for diabetes and obesity, particularly repeated doses in early childhood. Mechanistically, interactions between the microbiome and the host innate immune system, mediated by TLR4-LPS signaling, have been shown to meditate the metabolic benefits of caloric restriction. Further, gut microbes haven now been shown to regulate oxygen availability via butyrate production, thus protecting against the proliferation of pathogens such as E. coli and Salmonella. However, many microbial metabolites remain unidentified and their roles in obesity and diabetes remain to be determined.

The use of antimicrobials as adjuvant therapy for the treatment of obesity and insulin resistance: Effects and associated mechanisms

The intestinal microbiota has come to be considered an additional risk factor for the development of metabolic diseases. Considering the potential role of antimicrobials as modulators of the intestinal microbiota, they have been investigated for use in the adjuvant treatment of obesity and insulin resistance (IR). In this regard, the present manuscript aimed to review the effect of regular use of antimicrobials on the treatment of obesity and/or IR, as well as its associated mechanisms. The regular use of antimicrobials does not seem to influence the body weight and adiposity of its consumer. Regarding IR, clinical trials did not observe positive effects, on the other hand, most of the experimental studies observed an increase in insulin sensitivity. The mechanisms used by antimicrobials that could lead to the improvement of insulin sensitivity are dependent on the modulation of the intestinal microbiota. This modulation would lead to a reduction in the stimulation of the immune system, as a consequence of improved intestinal barrier and/or the reduction of gram-negative bacteria in the microbiota. In addition, the secretion of glucagon-like peptide-1 would be modulated by metabolites produced by the intestinal microbiota, such as secondary bile acids and short-chain fatty acids. Based on the results obtained to date, more studies should be performed to elucidate the effect of these drugs on obesity and IR, as well as the mechanisms involved. In addition, the cost-benefit of the regular use of antimicrobials should be investigated, as this practice may lead to the development of antimicrobial-resistant microorganisms.

Prebiotic Mannan-Oligosaccharides Augment the Hypoglycemic Effects of Metformin in Correlation with Modulating Gut Microbiota

Type 2 diabetes (T2D) induced by obesity and high-fat diet is significantly associated with gut microbiota dysbacteriosis. Because the first line clinical medicine of metformin has several intestinal drawbacks, combination usage of metformin with a prebiotic of konjac mannan-oligosaccharides (MOS) was conceived and implemented aiming to investigate whether there were some intestinal synergetic effects and how MOS would function. Composite treatment of metformin and MOS demonstrated synergistic effects on ameliorating insulin resistance and glucose tolerance, also on repairing islet and hepatic histology. In addition, MF+MOS altered the gut community composition and structure by decreasing the relative abundances of family Rikenellaceae and order Clostridiales while increasing an unnamed OTU05945 of family S24-7, Akkermansia muciniphila, and Bifidobacterium pseudolongum. The present study suggested that usage of MOS could augment the hypoglycemic effects of metformin in association with gut microbiota modulation, which could provide references for further medication.

How Do Structurally Distinct Compounds Exert Functionally Identical Effects in Combating Obesity?

Although the concept of inflammatory obesity remains to be widely accepted, a plethora of antibiotics, anti-inflammatory agents, mitochondrial uncouplers, and other structurally distinct compounds with unknown mechanisms have been demonstrated to exert functionally identical effects on weight reduction. Here we summarize a universal mechanism in which weight loss is modulated by mitochondrial biogenesis, which is correlated with conversion from the mitochondria-insufficient white adipose tissue to the mitochondria-abundant brown adipose tissue. This mechanistic description of inflammatory obesity may prove useful in the future for guiding pathology-based drug discovery for weight reduction.

A role for methanogens and methane in the regulation of GLP-1

INTRODUCTION

The gastrointestinal (GI) microbiome has emerged as a potential regulator of metabolism. However, the precise mechanisms of how microorganisms may influence physiology remain largely unknown. Interestingly, GI microorganisms, including methanogens, are localized within the same regions as the glucagon-like peptide-1 (GLP-1) secreting L cells. GLP-1 plays key roles appetite and glucose regulation. Furthermore, both methane and GLP-1 levels are altered in obese humans with metabolic disease. We predict that high-fat diet-induced obesity alters the abundance of GI methanogens and that methane may play a role in the GLP-1 secretory response from the L cell.

METHODS

To demonstrate this, GLP-1 secretion response and faecal methanogens were examined in mice given a high-fat diet for 14 weeks. In addition, the direct effect of methane on GLP-1 secretion was assessed in two L-cell models (NCI-H716 and GLUTag).

RESULTS

High-fat diet caused a significant increase in both GLP-1 secretion and faecal methanogen content. There was a direct correlation between GLP-1 secretion response and faecal methanogen levels. In L cells, methane stimulated GLP-1 secretion and enhanced intracellular cAMP content.

CONCLUSION

These results indicate that alterations in the methanogen communities occurring in obesity may play a vital role in directly enhancing GLP-1 secretion, and that methane can directly stimulate the secretion of GLP-1.

Breath methane concentrations and markers of obesity in patients with functional gastrointestinal disorders

Background

Obesity is associated with changes in the intestinal microbiome and methane-producing archaea may be involved in energy homeostasis.

Objective

The objective of this article is to investigate the associations between intestinal methane production, waist circumference and body mass index (BMI) as biomarkers for obesity.

Methods

Breath methane and hydrogen concentrations were measured over five hours following fructose or lactose ingestion in 1647 patients with functional gastrointestinal disorders. The relationships between gas concentrations and measures of obesity were investigated by stratifying gas concentration-time profiles by BMI and waist circumference, and, conversely, BMI and waist circumference by peak breath hydrogen and methane concentrations.

Results

Following fructose ingestion, patients with lower BMI and lesser waist circumference had greater breath methane concentrations (all p < 0.003). Conversely, patients with increased methane concentrations had lower BMI (p < 0.001) and waist circumference (p = 0.02). After lactose ingestion, BMI and waist circumference were not associated with significant differences in methane. However, greater methane concentrations were associated with a lower BMI (p < 0.002), but not with waist circumference.

Conclusion

In this large group of patients mainly negative associations between breath methane concentrations and anthropometric biomarkers of obesity were evident. Studies investigating microbial methane production and energy homoeostasis in different populations are of substantial interest to distinguish epiphenomena from true causality.A follow-up study was registered at Clinical trials.gov NCT02085889.

Selection of a cut-off for high- and low-methane producers using a spot-methane breath test: results from a large north American dataset of hydrogen, methane and carbon dioxide measurements in breath

BACKGROUND

Levels of breath methane, together with breath hydrogen, are determined by means of repeated collections of both, following ingestion of a carbohydrate substrate, at 15-20 minutes intervals, until 10 samples have been obtained. The frequent sampling is required to capture a rise of hydrogen emissions, which typically occur later in the test: in contrast, methane levels are typically elevated at baseline. If methane emissions represent the principal objective of the test, a spot methane test (i.e. a single-time-point sample taken after an overnight fast without administration of substrate) may be sufficient.

METHODS

We analysed 10-sample lactulose breath test data from 11 674 consecutive unique subjects who submitted samples to Commonwealth Laboratories (Salem, MA, USA) from sites in all of the states of the USA over a one-year period. The North American Consensus (NAC) guidelines criteria for breath testing served as a reference standard.

RESULTS

The overall prevalence of methane-positive subjects (by NAC criteria) was 20.4%, based on corrected methane results, and 18.9% based on raw data. In our USA dataset, the optimal cut-off level to maximize sensitivity and specificity was ≥4 ppm CH4, 94.5% [confidential interval (CI): 93.5-95.4%] and 95.0% (CI: 94.6-95.5%), respectively. The use of a correction factor (CF) (5% CO2 as numerator) led to reclassifications CH4-high to CH4-low in 0.7 % and CH4-low to CH4-high in 2.1%.

CONCLUSIONS

A cut-off value for methane at baseline of either ≥4 ppm, as in our USA dataset, or ≥ 5 ppm, as described in a single institution study, are both highly accurate in identifying subjects at baseline that would be diagnosed as 'methane-positive' in a 10-sample lactulose breath test for small intestinal bacterial overgrowth.