Ingestion of the soluble dietary fibre, polydextrose, increases calcium absorption and bone mineralization in normal and total-gastrectomized rats

We previously demonstrated that feeding a highly fermentable and water-soluble dietary fibre, guar-gum hydrolysate (GGH) increased intestinal absorption of insoluble Ca salts in total-gastrectomized rats. In the present study, we examined the effects of feeding a less fermentable and water-soluble fibre, polydextrose (PD), on Ca absorption and bone mineralization in the normal and total-gastrectomized rats in comparison with the effects of GGH. Apparent Ca absorption was severely lowered by gastrectomy, and PD feeding (50 g/kg diet) partially restored the reduction of Ca absorption similarly to GGH feeding (50 g/kg diet). PD feeding also increased the Ca absorption in normal rats, but not GGH feeding. Femur Ca concentration was reduced with gastrectomy. Feeding PD for 21 d increased the bone Ca concentration in both normal and gastrectomized rats, but GGH feeding did not. In rats fed PD, pH of the caecal contents was lower than in rats fed fibre-free and GGH diets; however, soluble Ca concentration in the caecal contents was not different between the diet groups. Short-chain fatty acid concentrations were much lower in the PD groups than in the GGH groups. We also examined in vitro Ca absorption by using everted sacs of the small intestine. Addition of PD to the serosal medium of the ileal sacs increased Ca absorption, but addition of GGH did not. These results suggest that the small intestine rather than the large intestine is responsible for the increase in Ca absorption in rats fed PD, and suggests that the mechanism for the increase by PD may be different from that by GGH.