A blend of dietary fibers increases urea disposal in the large intestine and lowers urinary nitrogen excretion in rats fed a low protein diet
1996
Younes, H. | Demigne, C. | Behr, S.R. | Garleb, K.A. | Remesy, C.
The presence of rapidly fermented indigestible carbohydrates in the diet has been shown to influence intestinal fermentations and the route of excretion of urea nitrogen. The objective of the present study was to determine the effects of a dietary fiber blend on nitrogen excretion in the rat. The dietary fiber blend studied (the "oligo/fiber blend") was comprised of 41.2% fructooligosaccharides, 17.7% insoluble oat fiber, 13.0% soy polysaccharide 10.3% gum arabic, and 4.4% carboxymethylcellulose, which provided a diversified source of soluble and insoluble fibers. Two levels (4% and 8%) of the oligo/fiber blend were added to diets containing low (8%) and normal (14%) protein levels. Plasma urea levels were reduced by another 37% when 8% oligo/fiber was added to the low protein diet. The reduction of plasma urea levels can be explained by nitrogen metabolism in the cecum. Feeding the oligo/fiber mix elicited a bacterial proliferation characterized by short chain fatty acid production, decreased cecal pH and marked cecal hypertrophy. At the 8% oligo/fiber level, urea nitrogen uptake from blood into the cecum was increased by over 2 fold. There was a compensatory increase in ammonia nitrogen flux from gut lumen to blood at the higher oligo/fiber levels, but on balance the direction of nitrogen flux remained strongly in the direction of the cecal lumen in the oligo/fiber fed rats. As a function of total nitrogen excretion, fecal nitrogen excretion was over 80% greater in rats fed the low protein diet than in rats fed the normal protein diet. With the addition of the oligo/fiber blend, the percentage of N in the feces was increased even further. In rats fed the 8% casein/8% oligo/fiber diet, fecal N excretion was nearly the same as urinary nitrogen excretion (approximately 50% of total nitrogen excretion by each route). In conclusion, by decreasing dietary protein and increasing the level of a dietary fiber blend within nutritionally acceptable ranges, plasma urea was decreased and the contribution of the kidneys to nitrogen excretion would be reduced.
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