Fermentable dietary fibers elevate urinary methylmalonate and decrease propionate oxidation in rats deprived of...

This study examines the effect of dietary fiber supplements of different degrees of bacterial fermentability on biochemical indicators of vitamin B-12 deficiency in rats. Groups of rats were fed a fiber-free diet deficient in vitamin B-12 or the fiber-free diet diluted with 5% of a poorly fermentable dietary fiber (cellulose, lignin or alginic acid) or a highly fermentable fiber (pectin, guar gum or xylan). Poorly fermentable fibers had no significant effect on apparent B-12 status, whereas the highly fermentable fibers significantly increased urinary methylmalonic acid and depressed oxidation of [14C]propionate to 14CO2. Pectin consistently induced significantly greater effects than did xylan or guar gum. The data are consistent with the hypothesis that fermentable fibers stimulate bacterial propionate production and exaggerate certain biochemical indicators of B-12 deficiency. Since pectin had a more pronounced effect than did other fermentable fibers, the possibility that pectin may also interfere with B-12 absorption requires further study.