Differential changes in the urinary excretion of two orally administered polyethylene glycol markers (PEG 900 and PEG 4000) in rats after feeding various carbohydrate gelling agents.

The urinary excretion of two orally administered polyethylene glycol markers (PEG 900 and PEG 4000) was measured in rats after feeding various carbohydrate gelling agents. Pectin, guaran, methylcellulose, and carrageenan were added (20% wt/wt) to a fiber-free control diet and were fed for 4 wk prior to the experiment. Excretion of 3H-PEG 900 and 14C-PEG 4000 was measured over a period of 96 h after administration of the markers in the drinking water. In general, the ratio of PEG 4000 to PEG 900 in the urine increased after fiber feeding: from 0.20 in the controls to 0.31, 0.37, 0.29, or 0.27 (medians) in the pectin-, guaran-, methylcellulose-, or carrageenan-fed group, respectively. The pattern of excretion of the two PEG markers in rats fed the fiber-free diet differed from that in the polysaccharide-fed rats. Pectin and guaran, two polysaccharides readily fermented by intestinal bacteria, led to a higher excretion of PEG 4000 but an unaltered excretion of PEG 900, whereas methylcellulose and carrageenan, two polysaccharides more inert against microbial degradation, were associated with a lower excretion of PEG 900 with unchanged excretion of PEG 4000. The study shows that polysaccharides, which may be representative of the soluble portion of dietary fiber, can influence the intestinal permeability of larger molecules. The microbiologically degradable polysaccharides in particular may lead to an increased absorption of larger molecules.