Comparative gastrointestinal and plasma cholesterol responses of rats fed on cholesterol-free diets supplemented with guar gum and sodium alginate

The present study investigated the digestion and cholesterol-lowering effec ts of the water-soluble NSP guar gum (GG) and sodium alginate (SA) in labor atory animals. Groups of five male Wistar strain rats were fed semi-purifie d cholesterol-free diets containing 0, 50 or 100 g NSP source/kg for 21 d w hich comprised a 14-d adaptation period followed by a 7-d balance period. W eight gain over the balance period and food conversion ratio decreased line arly with increasing NSP intake (P = 0.006 and P = 0.07 respectively). DM d igestibility decreased with increasing NSP intake (P = 0.001) and this effe ct was greater for SA-containing diets compared with GG-containing diets (P = 0.001). At the lower inclusion rate, 0.9-1.0 of the additional NSP was d igested, but this value fell to 0.8 for both NSP sources at the 100 g/kg in clusion rate, implying that the capacity for near complete digestion of the test NSP had been exceeded. Intestinal tissue mass was increased in respon se to inclusion of both NSP sources. Caecal digesta pH decreased linearly w ith additional GG, but increased slightly with consumption of SA. Total cae cal short-chain fatty acid concentrations (mu mol/g caecal contents) increa sed markedly with 50 g GG/kg but did not increase further with 100 g GG/kg, and were slightly lower than control values in rats consuming SA. Plasma c holesterol concentration fell linearly (P = 0.03) with increasing NSP in th e diet and the effect was similar for both GG and SA. Total output of faeca l bile acids rose in rats fed 50 g GG/kg and 50 g SA/kg (59 mu mol/7 d v. 2 4 mu mol/7 d for control mts) with no further increase at the higher inclus ion rate. These results show that SA has a strong hypocholesterolaemic effe ct in rats which is similar to that of GG, and that this effect is most lik ely to be mediated through an interruption in the entero-hepatic circulatio n of bile acids and not through increased hepatic supply of propionate from fermentation of the NSP in the large bowel.