Chemistry Reference
In-Depth Information
of the treatment seemed to be higher in women with lower initial bone density of the
spine (Coxam, 2005). In addition, genetic factors (such as vitamin D receptor gene
polymorphism) may also be associated with differences in sensitivity to the effects
of fructans (Abrams
et al., 2005).
A physiological retro-control mechanism provides good intestinal regulation of
Ca absorption, thanks to the calcium-binding protein. As it is highly regulated, a
high impact of fructans on this absorption is not expected. Overall, the increase of
Ca absorption under fructans would only have weak amplitude and few long-term
nutritional consequences.
3.4.2 Fructans and Absorption of Magnesium,
Copper, selenium, and Zinc
Positive effects of fructans on magnesium (Mg) absorption were naturally
expected in humans because, in contrast to Ca, Mg absorption occurs mainly pas-
sively and is not regulated depending on intakes and requirements. First results from
animal models indicated stimulant effects of fructans on Mg absorption (Rémésy
et al., 2002). This has been confirmed for sc-FOS and Mg absorption in a recent
study in humans: An increase of 11 percent of relative magnesium absorption was
observed after administration of 7 to 10 g/day sc-FOS during 5 weeks in postmeno-
pausal women (Tahiri
et al., 2001). Even on Mg, only a weak effect (increase by 10 to
20 percent) can be induced by FOS. However, about 20 percent of the population has
Mg intakes lower than two-thirds of RDA. This property of FOS, therefore, could
have an impact, even if small, on subjects with insufficient food Mg intakes.
A randomized double-blind, placebo-controlled trial showed that feeding 10 g of
FOS per day for 5 weeks increased the absorption of copper in healthy postmeno-
pausal women (Ducros
et al., 2005). However, no effects were seen in relation to zinc
and selenium uptake. This selectivity would suggest that factors other than simple
acidification of luminal contents were involved.
3.4.3 Fructans and Isoflavone Metabolism
Fructans may have a beneficial effect on the metabolism of isoflavones, which
have been shown to prevent postovariectomy bone loss in rats and mice (Tokunaga,
2004; Coxam, 2005). In ovariectomized mice (Ohta
et al., 2002) or rats (Mathey
et
al., 2004), two experimental models for postmenopausal osteoporosis, oligofructose
(sc-FOS) consumption has been shown to increase the bone-sparing effect of isofla-
vones by improving equol production. However, opposite results were reported in the
study of Zafar et al. (2004) as isoflavones enhanced Ca absorption without synergy
from inulin, and inulin decreased equol production in rats. In humans, a 2-month
intervention trial on 39 postmenopausal women showed that addition of prebiotics
(sc-FOS) or probiotics, by partially modulating the bioavailability of soy isoflavones,
improved parameters of bone turnover (Coxam, 2005).
