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Ellen G.H.M. van den Heuvel, Thomas Weidauer
Med Sci Monit 1999; 5(6): RA1231-1237
The current trends in healthy eating will increase levels of bulk-forming material in the diet, such as dietary fibre and other plant foods. Depending on the complex forming of such material the availability of absorbable calcium and other minerals may be impaired. It seems that non-digestible carbohydrates can inverse this effect. Major compounds belonging to this group are lactulose, fructo- and galacto-oligosaccharide and inulin. Lactose can only be regarded as a non-digestible carbohydrate in lactose-intolerant subjects and has been found not to affect or only minimally affect mineral absorption. The stimulation of mineral absorption by non-digestible carbohydrates takes place particularly in the ileum and the large intestine in different ways. An increase of passive transport mechanisms most likely occurs: one finding supporting the stimulation of passive mechanisms is that lactulose and calcitriol show additive action on calcium absorption. Degradation products of lactulose are SCFA which may stimulate transcellular transport of calcium. Whether or not active transport mechanisms are also involved in this process remains to be determined. pH in the distal ileum and the proximal colon is decreased by lactulose and other non-digestible carbohydrates. Increased calcium solubility by a reduced pH may increase paracellular calcium transport. Osmotic effects also may contribute to improved absorption of calcium and other minerals in that the 'tight junctions' become more permeable which may increase passive paracellular transport. Even though the mechanisms have not been fully elucidated, it can be said that lactulose enhances absorption of calcium and probably other minerals. The scale at which this occurs may be of clinical relevance in humans, particularly at an advanced age, since calcium absorption decreases during old age. Confirmatory studies will be needed to determine the significance of these results for the therapeutic or preventative use of lactulose in osteoporosis and other decalcification syndromes, and in colon cancer.