The effect of fructooligosaccharides with various degrees of polymerization on calcium bioavailability in the growing rat.

Maximizing peak bone mass during adolescence may be the key to postponing and perhaps preventing bone fractures due to osteoporosis in later life. One mechanism to maximize peak bone mass is to maximize calcium absorption, and it has been suggested that inulin and oligofructose might be one of the ways of doing so. In this study, fructooligosaccharides with various degrees of polymerization have been compared in terms of impact on calcium absorption, bone density, and excretion of collagen cross-links in the young adult male rat. The various oligosaccharides were oligofructose (DP2-8), inulin (DP>23), and a mixture of 92% inulin and 8% short-chain oligofructose (DP2-8). Measuring ex vivo bone mineral density (BMD) and bone mineral content (BMC) showed that BMD was significantly higher in the group fed inulin (DP>23) in both femurs, whereas BMC was significantly higher in the spine. The excretion of fragments of Type 1 collagen decreased in all groups over the 4 weeks of feeding, but the decrease was most significant in the group fed inulin (DP>23). Several hypotheses have been offered to explain the effect of the fructooligosaccharides on calcium absorption and retention. These include the production of organic acids that would acidify the luminal contents and enhance solubility and hence absorption, or possibly a mechanism via calbindinD9k. This study is unique in that it compares the different fructooligosaccharides in the same model, and it clearly shows that the various fructans do not have the same effect. In our model, inulin (DP>23) had the most significant effect on calcium bioavailability.