Influence of dietary carboxymethylcellulose on the apparent absorption of calcium, magnesium and phosphorus in rats

Abstract

Introduction Dietary pectin vs cellulose has been shown to enhance apparent magnesium absorption in rats (unpublished data). This observation supports that of V ahouny et al. (1987), indicating that pectin feeding produced a more positive balance of magnesium in young, growing rats than did cellulose feeding. Pectin is a soluble, viscous and readily fermentable non‐starch polysaccharide, but is not digested by animal enzymes. Pectin feeding raises the viscosity of small intestinal digesta in rats (J udd and T ruswell 1985). The increase in magnesium absorption seen after pectin feeding could relate to its fermentation, which may lower the pH of the small intestinal digesta, which in turn raises the solubility of minerals, rendering them more available for absorption. Both dietary lactulose and lactose, which are not digestible but highly fermentable, lower the pH of small intestinal digesta and increase mineral absorption in rats (H eijnen et al. 1993). The influence of viscosity per se on mineral absorption is unknown. In contrast to the above‐mentioned mechanism, the observed stimulatory effect of pectin feeding on magnesium absorption (unpublished data) could relate to viscosity of small intestinal contents. To provide clues as to this possibility, the model compound carboxymethylcellulose (CMC) may be used. This compound is not digested by animal enzymes, is non‐fermentable, but is highly viscous and has been shown to raise the viscosity of small intestinal contents in broiler chickens (S mits et al. 1997). Thus we fed rats on diets with different levels of CMC to study the influence of digesta viscosity on apparent absorption of calcium, magnesium and phosphorus.