The fibres are most commonly used as a fat and sugar replacer, and has increasingly been linked to gut health benefits, due to their action as prebiotics to promote the growth of beneficial intestinal microflora populations.
But an increasing body of science is emerging linking the ingredients to help control blood sugar levels, reduce cholesterol, and boost bone strength, with inulin maker Orafti highly active in this area.
The new research, published in the current issue of the journal Nutrition Research (Vol. 26, pp. 413-420), adds to this body of science by reporting that rats supplemented with Raftilose (Orafti) - an enriched form of inulin containing a specific distribution of different chain lengths of inulin and oligofructose - boosted calcium absorption by about 40 per cent, and led to greater bone strength.
"These results indicate an important role of fructo-oligosaccharides [inulin, oligofructose] in the maintenance of healthy bones," wrote lead researcher Alexandre Lobo from the University of Sao Paulo.
The researchers divided 16 male Wistar rats into two groups and fed a control diet containing 7.5 grams of calcium per kilogram of diet for 23 days. One group of eight animals were supplemented with five per cent inulin, oligofructose.
At the end of the intervention period the researchers reported that calcium absorption in the supplemented group increased by 44 per cent, compared to the control diet group. The bone mineral density in the middle of the thigh bone (midshaft femur) was 0.02 grams per sq. cm greater for the supplemented group, compared to the control diet group.
The biomechanical properties, measures of the strength of the bones, also increased significantly for the inulin, oligofructose-supplemented groups, reported the researchers.
No adverse effects were observed for the inulin, oligofructose-supplemented groups, but some increase in the moisture content of the animals' faeces was recorded.
The mechanism of the benefits has been discussed by earlier studies, said Lobo. The prebiotic is thought to work by changing the flora in the colon, with the more slowly fermented inulin acting as a selective 'fuel' for this modified flora, which is kept metabolically active further in the gut.
This selective fermentation pattern results in the production of short chain fatty acids, which decrease the pH within the colon, improving the solubility of the calcium present. The calcium is then better absorbed into the body.
"Assuming that the fracture risk results from a progressive loss of bone mass in adulthood and that this loss is lower in people that formed bone mass more effectively in childhood and adolescence, [inulin and oligofructose] may be regarded as a food component with bone health enhancer property to early ages," concluded the researchers.
A spokeswoman from the National Osteoporosis Society (NOS) told NutraIngredients.com in July that the preliminary data from animal and experimental studies on calcium absorption were promising, but called for more human across the age span to further clarify the links with improvements in bone health or reductions in osteoporosis risk.
Such human studies are increasing, with a significant number of studies into the role of the prebiotics on improving the bone health of adolescent girls. Indeed, one such study reported that girls and boys aged between 9 and 12 supplemented with a mixture of oligofructose and long-chain inulin had an additional net accretion of calcium of 30 milligrams per day, compared to the controls who received a placebo (American Journal of Clinical Nutrition, 2005, Vol. 82, pp. 471-476).
The benefits of the prebiotic fibres will continue with the imminent opening of Orafti's 5th Research Conference in Boston later this week. NutraIngredients.com will be at Harvard Medical School, Boston to report on the conference.
The full programme includes key presentations by world-renowned prebiotics experts. A session is dedicated to the role of inulin and oligofructose on bone health, and will be chaired by Professor Connie Weaver from Purdue University. Presentations include, "Diet, nutrition and bone health," by Professor Kevin Cashman (University College Cork), "Overview of experimental data with Inulin and Oligofructose," by Dr. Katharina Scholz-Ahrens (Federal Dairy Research Center, Germany), "Role of Inulin and Oligofructose in adolescents," by Dr. Steve Abrams (Baylor College of Medicine and the Texas Children's Hospital), and "Current data with Inulin and Oligofructose in adults," by Dr. Veronique Coxam (Institut National de la Recherche Agronomique, INRA, France).
Osteoporosis is estimated to affect about 75m people in Europe, the USA and Japan. According to the International Osteoporosis Foundation, the total direct cost of osteoporotic fractures is €31.7bn in Europe, and 17.5bn in the US (2002 figure). The total annual cost of osteoporosis in the UK alone is over £1.7bn (€2.5bn), equivalent to £5m (€7.3m) each day.