Nondigestible
oligosaccharides have been shown to increase the absorption of several minerals (
calcium,
magnesium, in some cases
phosphorus) and
trace elements (mainly
copper,
iron,
zinc).
Inulin-type
fructans including
oligofructose and fructooligosaccharides derived from
sucrose by enzymatic transfructosylation are the best investigated
food ingredients in this respect. The stimulation of absorption was more pronounced when the demand for
calcium was high, i.e., in animals in the rapid growing stage and in animals with impaired
calcium absorption because of either
ovariectomy or
gastrectomy. Even a small stimulation of
calcium absorption increased the
mineral accumulation in the skeleton because of its persisting effect over months.
Inulin-type
fructans stimulated
mineral absorption and bone
mineral accretion when combined with probiotic lactobacilli and in the presence of
antibiotics. Direct comparison of different
inulin-type
fructans revealed a more pronounced effect by
inulin or a mixture of long-chain
inulin and
oligofructose than by
oligofructose alone. Mechanisms on how
inulin-type
fructans mediate this effect include acidification of the intestinal lumen by
short-chain fatty acids increasing solubility of minerals in the gut, enlargement of the absorption surface, increased expression of
calcium-binding proteins mainly in the large intestine, modulated expression of bone-relevant
cytokines, suppression of
bone resorption, increased bioavailability of
phytoestrogens, and, via stimulation of beneficial commensal microorganisms, increase of
calcium uptake by enterocytes. Under certain conditions,
inulin-type
fructans may improve
mineral absorption by their impact on the amelioration of gut health including stabilization of the intestinal flora and reduction of
inflammation. The abundance of reports indicate that
inulin-type
fructans are promising substances that could help to improve the supply with available
calcium in human nutrition and by this contribute to bone health.