SCF, a nondigestible carbohydrate, increased calcium absorption in free-living adolescent females. Two groups of bacteria may be involved, one directly fermenting SCF and the second fermenting SCF metabolites further, thereby promoting increased calcium absorption. This trial was registered at clinicaltrials.gov as NCT01660503.

Increasing interest in functional foods has driven discovery in the area of bioactive compounds. Prebiotics are non-digestible carbohydrate compounds that, when consumed, elicit health benefits and aid in the prevention and treatment of chronic diseases. While prebiotics have been shown to improve a number of chronic, inflammatory conditions, growing evidence exists for prebiotic effects on calcium metabolism and bone health. These novel dietary fibers have been shown to increase calcium absorption in the lower intestines of both preclinical and human models. Rodent models have also been imperative for understanding prebiotic effects on bone mineral density and measures of skeletal strength. Although fewer data are available for humans, bone-related prebiotic effects exist across the lifecycle, suggesting benefits for attainment of peak bone mass during adolescence and minimized bone resorption among postmenopausal women. These effects are thought to occur through prebiotic–microbe interactions in the large intestine. Current prebiotic mechanisms for improved mineral absorption and skeletal health include alterations in gut microbiota composition, production of short-chain fatty acids, altered intestinal pH, biomarker modification, and immune system regulation. While the majority of available data support improved mineral bioavailability, emerging evidence suggests alternate microbial roles and the presence of an intricate gut–bone signaling axis. Overall, the current scientific literature supports prebiotic consumption as a cost-effective and sustainable approach for improved skeletal health and/or fracture prevention. The goal of this review is to discuss both foundational and recent research in the area of prebiotics, mineral metabolism, and bone health.

Adolescence is a time for rapid growth that represents an opportunity to influence peak bone mass. Prebiotic agents, such as galactooligosaccharides (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 5 g GOS for three 3-week periods in a random order. Fractional Ca absorption was determined from urinary Ca excretion over 48 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 48 h treatment with control, 5 and 10 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, 0·02), but it was not a dose -response relationship. The increase in absorption was greatest in the urine collected after 24 h, which is consistent with lower gut absorption. Faecal bifidobacteria increased (control 10·89 (SD 13·86), 5 g GOS 22·80 (SD 15·74) and 10 g GOS 11·54 (SD 14·20)) with the GOS treatment (P,0·03). The results suggest that daily consumption of 5 g GOS increases Ca absorption, which may be mediated by the gut microbiota, specifically bifidobacteria.Key words: Prebiotic: Calcium absorption: Bifidobacteria: Galacto-oligosaccharides Prebiotics have become more prevalent in foodstuffs with the growing interest in functional foods and their role in health and disease prevention. Non-digestible oligosaccharides meet the FAO and the WHO definition of a prebiotic (1) as they are thought to influence indigenous bacteria and have beneficial physiological effects, including a role in bone health. Adolescence is an important time period for maximising peak bone mass to prevent the development of osteoporosis later in life. The high bone mineral accrual velocity that occurs during adolescence presents a unique opportunity to influence peak bone mass through modifiable lifestyle factors, such as diet and exercise. Current Ca consumption is well under the recommended 1300 mg/d for adolescents in the USA (2) . An alternative approach to improving Ca nutrition is to increase Ca bioavailability. A growing body of literature suggests that non-digestible oligosaccharides, including galacto-oligosaccharides (GOS), have beneficial effects on Ca metabolism and bone health through increasing Ca absorption (3) .GOS are non-digestible carbohydrates consisting of chains of galactose with a glucose end piece, varying in chain length from two to eight monomers. They are produced by means of enzymatic conversion of lactose, and are being used on a large scale ...

Soluble maize fibre (SCF) has been found to significantly improve bone mineral density and strength in growing rats compared with several other novel prebiotic fibres. The objective of the present study was to investigate the effect of SCF on Ca absorption and retention in pubertal children by studying the potential absorption mechanisms of the intestinal microbiota. A total of twenty-four adolescent boys and girls (12 -15 years) participated in two 3-week metabolic balance studies testing 0 g/d SCF (control (CON) treatment) and 12 g/d SCF (SCF treatment) in a random order by inclusion in a low-Ca diet (600 mg/d). Fractional Ca absorption was measured at the end of the two intervention periods using a dual-stable isotope method. Diet composites and faecal and urine samples were collected daily and analysed for Ca content. Ca retention was calculated as dietary Ca intake minus Ca excretion in faeces and urine over the last 2 weeks. Microbial community composition in the faecal samples collected at the beginning and end of each session was determined by 454 pyrosequencing of the PCR-amplified 16S ribosomal RNA gene. Fractional Ca absorption was 12 % higher (41 mg/d) after the SCF treatment compared with that after the CON treatment (0·664 (SD 0·129) and 0·595 (SD 0·142), respectively; P¼0·02), but Ca retention was unaffected. The average proportion of bacteria of the phylum Bacteroidetes was significantly greater in the participants after the SCF treatment than after the CON treatment. These results suggest that moderate daily intake of SCF, a well-tolerated prebiotic fibre, increases short-term Ca absorption in adolescents consuming less than the recommended amounts of Ca.Key words: Prebiotics: Calcium absorption: Microbiota: Soluble maize fibre Adolescence is an important stage of life for bone health that provides a unique opportunity to maximise mineral retention and prevent the risk of osteoporosis-related fractures later in life. Because Ca is becoming increasingly deficient in the diet due to a decrease in milk consumption (1,2) , there is strong interest in functional food ingredients for enhancing Ca utilisation. Non-digestible oligosaccharides, including fructo-oligosaccharides (3,4) and galacto-oligosaccharides (5) , have been reported to be associated with increased Ca absorption. In animal studies, these carbohydrate compounds have been found to be associated with increases in bone mineral density (BMD) (6 -8) as well as improved bone geometry and strength (7,9,10) . The increase in Ca absorption and subsequent improvements in bone health are possibly mediated by microbial fermentation. Bongers & Van den Heuvel (11) suggested that SCFA produced by microbial fermentation can produce an acidic intestinal environment ideal for increasing the solubility and transcellular absorption of Ca.We had compared eight novel fibres for their effects on Ca utilisation and bone properties in a growing rat model (12) . Soluble maize fibre (SCF) was found to have effects similar to those of soluble fibre dextr...