Dietary pectin shortens the biologic half-life of vitamin B-12 in rats by increasing fecal and urinary losses.
As little as 5% of pectin added to a fiber-free diet elevates urinary methylmalonic acid (MMA) severalfold in vitamin B-12--deprived rats. The present study examines whether increased urinary MMA reflects lower vitamin B-12 status or occurs only because of fermentation of pectin by intestinal bacteria and increased production of propionate, a precursor of MMA. By monitoring urinary and fecal excretion of 57Co after a tracer dose of [57Co]vitamin B-12, we found the biologic half-life of vitamin B-12 to be 59 d for rats fed a fiber-free diet and only 19 d for rats fed a 5% pectin diet. Also, pectin-fed rats oxidized only 12% of a 1-mmol dose of [14C]propionate to 14CO2 in 2 h, whereas rats fed the fiber-free diet expired 33% of the dose. Finally, high urinary MMA persisted even after the removal of pectin from the diet. We conclude that dietary pectin accelerates vitamin B-12 depletion in rats, possibly by interfering with enterohepatic recycling of vitamin B-12. By stimulating microbial propionate production, pectin and other fermentable fibers may also contribute to increased urinary MMA in vitamin B-12 deficiency, but a larger propionate pool does not account for the other effects of pectin on vitamin B-12 status.
Cullen
R W
RW
Department of Nutritional Sciences, University of California, Berkeley 94720.
Oace
S M
SM
D000818:Animals; D001835:Body Weight; D003037:Cobalt Radioisotopes; D004043:Dietary Fiber / Q000494:pharmacology; D005243:Feces / Q000032:analysis; D006207:Half-Life; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008764:Methylmalonic Acid / Q000652:urine; D010084:Oxidation-Reduction; D010368:Pectins / Q000494:pharmacology*; D011422:Propionates / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D014805:Vitamin B 12 / Q000378:metabolism* / Q000652:urine
D003037:Cobalt Radioisotopes; D004043:Dietary Fiber; D011422:Propionates; D010368:Pectins; D008764:Methylmalonic Acid; D014805:Vitamin B 12