Fascinating studies on oligosaccharides in milk have tied together non-digestible oligosaccharides, the gut microbiota, health and milk. These non-digestible oligosaccharides that can improve health – called prebiotics – can also be derived from plant material. Admittedly not designed by nature to function in the mammalian digestive tract the way milk-derived oligosaccharides are, there is mounting evidence that they have important health effects that may be important to dairy. A recent study showed that consumption of 5 g/day of a plant-based galactooligosaccharide (GOS) improved absorption of calcium in girls 10-13 years of age consuming a fiber-controlled (at 15 g/d, excluding GOS) diet (Whisner et al. 2013). And like milk-derived oligosaccharides, GOS appears to function by stimulation of the Bifidobacterium components of the human microbiota.
This well-designed study evaluated three doses of GOS in a randomized, crossover design. Whisner et al. fed 31 healthy girls (10–13 years old) 0, 2.5 or 5 g GOS in a smoothie drink twice daily for three 3-week periods in a random order. Crossover occurred after 2-week washout periods. Fractional calcium absorption was determined at the end of each 3-week period. In addition, fecal microbiota and specifically bifidobacteria were assessed by PCR–denaturing gradient gel electrophoresis and quantitative PCR.
The study found that calcium absorption increased significantly compared to zero-intake control, but not in a dose-dependent manner. Furthermore, authors found that the increase in calcium absorption was greatest after 24 h, suggesting the impact was on absorption occurring in the lower gut. Fecal bifidobacteria as a percentage of total bacteria increased. This is consistent with an observation by Davis et al. (2011), who demonstrated specificity of Bifidobacterium response to GOS. But the Bifidobacterium response was not dose-dependent either, possibly due to a postulated threshold effect. Individuals with higher baseline quantities of bifidobacteria may show a limited increase in bifidobacteria up to a certain threshold level. Weekly assessments of gastrointestinal symptoms (bloating, abdominal pain, diarrhea, flatulence, bowel movement frequency and bowel movement consistency) showed no increase due to the experimental diets.
This study demonstrates the potential value of incorporating GOS into the diets of healthy girls to improve calcium status. Low calcium intake in American adolescents could be countered by increased calcium bioavailability. GOS may be an important partner for dairy products to improve peak bone mass accrual during adolescence.
Whisner CM, Martin BR, Schoterman MH, Nakatsu CH, McCabe LD, McCabe GP, Wastney ME, van den Heuvel EG, Weaver CM. Galacto-oligosaccharides increase calcium absorption and gut bifidobacteria in young girls: a double-blind cross-over trial. Br J Nutr. 2013 Mar 14:1-12.
Davis LM, Martínez I, Walter J, Goin C, Hutkins RW. Barcoded pyrosequencing reveals that consumption of galactooligosaccharides results in a highly specific bifidogenic response in humans. PLoS One. 2011;6(9):e25200.