Lack of effect of lactose digestion status on baseline fecal micoflora

Lactose tolerance test as an alternative to hydrogen breath test in the study of lactose malabsorption

Objectives

Lactose malabsorption is generally assessed by hydrogen breath testing (HBT). However, this test is not recommended in patients with high baseline hydrogen concentrations (H₂B). In addition, breath testing is not recommended in the current situation created by the COVID-19 pandemic, due to the potential infectiveness of the samples. The objective is to assess concordance between HBT and lactose tolerance test (LTT) depending on H₂B concentrations.

Methods

A total of 430 patients (40 years, Q1-Q3 = 28-54 years; 66.7% women) suspected of lactose malabsorption were included in the study. Breath and heparinized blood samples were collected at baseline and sequentially after the intake of 50 g of lactose, to measure hydrogen in breath and glycemia in blood, respectively.

Results

H₂B was <10 ppm in 69.5% of subjects; 10-20 ppm in 14.7%; and >20 ppm in 15.8% of subjects. In patients with H₂B <20 ppm, concordance between HBT and LTT was moderate and consistently improved when the cut-off in LTT was set at 15 mg/dL. The increase in hydrogen and glucose correlated negatively (r=-0.389; p<0.05). The increase in glycemia during LTT was not influenced by H₂B levels obtained in HBT.

Conclusions

LTT emerges as an alternative to HBT to assess lactose malabsorption in the presence of high H₂B levels or when breath testing is not recommended by the circumstances. The best concordance was obtained when the cut-off for LTT was set at 15 mg/dL.

Contribution of Colonic Fermentation and Fecal Water Toxicity to the Pathophysiology of Lactose-Intolerance

Whether or not abdominal symptoms occur in subjects with small intestinal lactose malabsorption might depend on differences in colonic fermentation. To evaluate this hypothesis, we collected fecal samples from subjects with lactose malabsorption with abdominal complaints (LM-IT, n = 11) and without abdominal complaints (LM-T, n = 8) and subjects with normal lactose digestion (NLD, n = 15). Lactose malabsorption was diagnosed using a ¹³C-lactose breath test. Colonic fermentation was characterized in fecal samples at baseline and after incubation with lactose for 3 h, 6 h and 24 h through a metabolomics approach using gas chromatography-mass spectrometry (GC-MS). Fecal water cytotoxicity was analyzed using a colorimetric assay. Fecal water cytotoxicity was not different between the three groups (Kruskall-Wallis p = 0.164). Cluster analysis of the metabolite patterns revealed separate clusters for NLD, LM-T and LM-IT samples at baseline and after 24 h incubation with lactose. Levels of 5-methyl-2-furancarboxaldehyde were significantly higher in LM-IT and LM-T compared to NLD whereas those of an unidentified aldehyde were significantly higher in LM-IT compared to LM-T and NLD. Incubation with lactose increased short chain fatty acid (SCFA) concentrations more in LM-IT and LM-T compared to NLD. In conclusion, fermentation patterns were clearly different in NLD, LM-IT and LM-T, but not related to differences in fecal water cytotoxicity.

Meta-analysis: the diagnostic accuracy of lactose breath hydrogen or lactose tolerance tests for predicting the North European lactase polymorphism C/T-13910

BACKGROUND

  The diagnostic accuracy of two indirect tests of lactose digestion, lactose breath hydrogen and lactose tolerance tests, have not been systematically reviewed for comparison with available publications on genotype.

AIM

  To perform a meta-analysis of available studies that compares the north-European genetic polymorphism C/T-13910 with the lactose breath hydrogen and the lactose tolerance tests, to determine their ability to predict geno/phenotype relationships. We examine the effects of lactose loading dose, inclusion of children and latitudes of study centre on comparative outcome.

METHODS

  An electronic database of the literature as well as individual references in articles were searched with the theme of genetics of lactase and comparisons with breath or lactose tolerance tests were carried out. Random effect and fixed effect models were used for breath and lactose tolerance tests respectively, to report summary accuracy measures with 95% confidence intervals (CI).

RESULTS

  The search revealed 19 studies: 17 evaluated breath hydrogen, five lactose tolerance test (3/17 overlapped). Overall sensitivity was 0.88 (CI, 0.85-0.90), specificity was 0.85 (CI, 0.82-0.87) for breath test. Heterogeneity was explored by adjusting for studies including children, high or low dose lactose and to some extent by site of study. The lactose tolerance test showed sensitivity of 0.94 (0.9-0.97) and specificity of 0.90 (0.84-0.95) with a nonsignificant heterogeneity.

CONCLUSION

  The diagnostic accuracy of both tests individually reflects expected geno/phenotypes when the populations are well defined.

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 maldigesters 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 unitsg 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 scorestogether, 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.