Changes in gut microbiota and lactose intolerance symptoms before and after daily lactose supplementation in individuals with the lactase nonpersistent genotype

About 70∼100% of the Asian adult population is lactase non-persistent (LNP). The literature shows that many individuals with the LNP-genotype can consume ≤12g of lactose without experiencing gastrointestinal discomfort. Repetitive consumption of lactose may reduce intolerance symptoms via adaptation of the gut microbiota. This study aimed to assess the effects of daily consumption of incremental lactose doses on microbiota composition and function, and intolerance symptoms. Twenty-five healthy adults of Asian origin, carrying the LNP-genotype were included in this 12-week before-and-after intervention trial. Participants consumed gradually increasing lactose doses from 3 to 6g to 12g twice daily, each daily dose of 6, 12, or 24g being provided for 4 consecutive weeks. Participants handed in repeated stool samples and underwent a 25g lactose challenge hydrogen breath test (HBT) before and after the 12-week intervention. Daily gastrointestinal symptoms and total symptom scores (TSS) during the lactose challenge were recorded. A significant increase from 5.5±7.6% to 10.4±9.6% was observed in Bifidobacterium relative abundance after the intervention (p=0.009), accompanied by a two-fold increase (570±269U/g; p<0.001) in fecal β-galactosidase activity compared to baseline (272±158U/g). A 1.5-fold decrease (iAUC; p=0.01) in expired hydrogen was observed during the second HBT (38±35ppm·minutes), compared to the baseline HBT (57±38ppm·minutes). There was a non-significant decrease in TSS (10.6±8.3 before vs 8.1±7.2 after intervention; p=0.09). Daily consumption of lactose was well-tolerated, with mild to no gastrointestinal complaints reported during the intervention. Increased levels of Bifidobacterium indicate an adaptation of the gut microbiota upon repetitive consumption of incremental doses of lactose, which was well-tolerated as demonstrated by reduced expired hydrogen levels during the second 25g lactose HBT. Bifidobacteria metabolize lactose without gas production thereby potentially reducing intestinal gas formation in the gut of individuals with the LNP-genotype. This increased lactose tolerance possibly lifts the necessity to remove nutrient-rich dairy foods completely from the diet. The trial is registered at the International Clinical Trials Registry Platform: NL9516 The effect of dietary lactose in lactase non-persistent individuals on gut microbiota