Varying dietary concentrations of fructooligosaccharides affect apparent absorption and balance of minerals in growing rats

Carbohydrates that bypass digestion in the small intestine and are fermented in the large intestine may affect the absorption of certain minerals. A study was conducted to determine the effect of varying dietary concentrations of fructooligosaccharides (FOS) on the apparent digestibility and balance of certain macro and trace minerals. Forty growing male Sprague-Dawley rats were assigned one of four treatments: 1) purified diet (control); 2) purified diet + 1% FOS; 3) purified diet + 3% FOS; or 4) purified diet + 5% FOS. Rats were acclimated to their metabolic cages for 5 d, after which they were subjected to a 10-d growth period, followed by a 7-d balance period in which diets were restricted to 90% ad libitum intake of the lowest consuming rat. Cecal pH decreased (P < 0.01) as dietary FOS concentration increased, reflecting an increase in cecal short-chain fatty acid concentration. In addition, FOS supplementation increased (P < 0.01) fecal N excretion, although N balance was similar among groups. Apparent absorption of Mg increased linearly (P < 0.01) as FOS concentration increased in the diet; however, Mg balance (mg/d) was similar (P > 0.10) across treatments. The macrominerals (Ca, P, Mg, Na, Cl, K) and trace minerals (Cu, Fe, Mn, Zn) were in a positive balance for all experimental treatments. However, Cu absorption decreased with increasing FOS concentration. This may be explained by an increase in fecal microbial mass which would contain a relatively significant amount of Cu or by an increase in hepatic bile Cu excretion. These results suggest that dietary FOS alters acute Cu metabolism in growing rats. (C) 1998 Elsevier Science Inc.