Galacto-oligosaccharides increase calcium absorption and gut bifidobacteria in young girls: A double-blind cross-over trial

Adolescence is a time for rapid growth that represents an opportunity to influence peak bone mass. Prebiotic agents, such as galacto-oligosaccharides (GOS), increase Ca absorption in animal models and postmenopausal women. The objectives of the present study were to investigate the dose-response relationship of GOS supplementation on Ca absorption during growth and to assess changes in colonic microbiota to better understand the mechanism by which GOS is acting. A total of thirty-one healthy adolescent girls aged 10-13 years consumed smoothie drinks twice daily with 0, 2·5 or 5Â g GOS for three 3-week periods in a random order. Fractional Ca absorption was determined from urinary Ca excretion over 48Â h at the end of each 3-week period using a dual stable isotope method. Faecal microbiota and bifidobacteria were assessed by PCR-denaturing gradient gel electrophoresis and quantitative PCR. Fractional Ca absorption after the 48Â h treatment with control, 5 and 10Â g GOS/d was 0·393 (sd 0·092), 0·444 (sd 0·086) and 0·419 (sd 0·099), respectively. Significant improvements in Ca absorption were seen with both low and high doses of GOS compared with the control (P<Â 0·02), but it was not a dose-response relationship. The increase in absorption was greatest in the urine collected after 24Â h, which is consistent with lower gut absorption. Faecal bifidobacteria increased (control 10·89 (sd 13·86), 5Â g GOS 22·80 (sd 15·74) and 10Â g GOS 11·54 (sd 14·20)) with the GOS treatment (P<Â 0·03). The results suggest that daily consumption of 5Â g GOS increases Ca absorption, which may be mediated by the gut microbiota, specifically bifidobacteria.