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Fermentable Dietary Fibers Elevate Urinary Methylmalonate and Decrease Propionate Oxidation in Rats Deprived of Vitamin B-12^1,2,3,

Department of Nutritional Sciences, University of California, Berkeley, CA 94720

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.

KEY WORDS: • vitamin B-12 • dietary fiber • intestinal flora • pectin • rat • methylmalonate • propionate

¹ Supported in part by National Institutes of Health Grant AM-19970.

² Presented in part at the 64th Annual Meeting of the Federation of American Societies for Experimental Biology, Anaheim, CA, April 1980 [Cullen, R. W. & Oace, S. M. (1980) Impact on B-12 status of pectin and six dietary fibers in rats. Fed. Proc. 39: 785 (abs.)].

³ These data are taken from the dissertation submitted by R. W. Cullen to the Graduate Division, University of California, Berkeley, in partial fulfillment of the requirements for the Ph.D. in Nutrition.

⁴ Present address: Department of Human Nutrition and Food Systems Management, Winthrop College, Rock Hill, SC 29733.

⁵ To whom reprint requests should be addressed.

Manuscript received 18 January 1989. Revision accepted 29 March 1989.