EXPERIMENTAL NUTRITION
DIETARY FIBER AND VITAMIN
812
BALANCE
lnclusion of either cellulose or pectin in a fiber-free basal diet increased the rate of fecal excretion of vitamin B I2 In addifion, pectin supplements stimulated a m e - to 2 1-fold increase in urinary excretion of rnethylrnalonic acid
Key Words vitamin B12 deficiency rnethylrnalonic acid. dietary fiber cellulose pectin
The recent speculation by Burkitt et a1.l that the lack of fiber in the Western diet may contribute to the development of a variety of maladies including several gastrointestinal disorders and heart disease has provoked a vigorous and hasty response in the marketplace. With little regard for the wide range of chemical differences among the common fibers and without awaiting a systematic experimental evaluation of the valid benefits and potential hazards of supplementation. the popular outcry for "more wholesome food" has been speedily satisfied by the insertion of an assortment of fibers into many components of our daily fare. Two polysaccharides which have been included in such fiber supplements are cellulose and pectin. Cellulose is a linear polymer of Dglucose in a p-( 1 . -4) linkage. It is abundant as a plant structural polysaccharide. Pectin is also a plant polysaccharide, but its repeating unit is methyl ester galacturonic acid partially in the form of the methyl ester. Neither substance is digestible by mammalian enzymes but both may be hydrolyzed by enzymes from microorganisms in the human lower intestine. Many of the questions concerning the appropriate intake of fiber hinge upon the characteristics of the mixed microbial population which is favored or sustained by the dietary additives. Cullen and Oacez have examined the effects of cellulose or pectin supplements upon vitamin B12 metabolism in the rat. A basal B12-deficient fiber-free diet was employed 116
NUTRlTlON REVlEWS VOL. 37. NO. 4 / APRIL 1979
which consisted of 20 percent soybean protein, 70 percent glucose monohydrate, 5 percent corn oil, 0.5 percent D, L-methionine and mineral and vitamin mixes free of both cobalt and vitamin BIZ. Cellulose was added to this diet to achieve final concentrations of 10, 20, 30, 40 or 50 percent. A second series of rations contained 5, 10, 15, 20 or 30 percent of unhydrated pectin. Male 28-day-old Fischer rats were maintained on these diets in groups of six rats per treatment for ten weeks. Their growth and food intake was monitored and feces and urine were collected periodically during this time. Growth and food efficiency were reported for the first four weeks of the study. Despite the unavoidable dilution in calories, body weight gain was not affected significantly during this period in the 10 to 40 percent cellulose-diet groups. A slight decline in gain was observed for those rats fed the 50 percent cellulose ration ( 108 6 g) as compared to control animals 5 9). Since food fed the fiber-free diet (128 efficiency calculated as gain per unit of basal diet consumed was constant over the entire range, it was presumed that the difference in body weight observed in the 50 percent cellulose-consuming group was attributable to energy deficit and not to a deficiency of any essential nutrients. In contrast, food intake dropped and weight gain was progressively reduced as the proportion of dietary pectin was increased from 10 to 20 percent and the group fed 30 percent pectin lost weight. In this series, food efficiency of the fiber-free portion of the 0.004 in the diet also declined from 0.355 basal group to 0.161 L 0.029 in the 20 percent t
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pectin group suggesting more serious problems than caloric dilution. Comparisons of the weight of feces and the fiber consumed indicated that little of the cellulose additive was degraded during its passage through the alimentary canal whereas most of the pectin was metabolized. In the cellulose experiment, even the lowest fiber intake per 48 hours (3.7 g) was accompanied by a significant increase in fecal weight as compared to the fiber-free ration (5.0 g vs 1.5 g, P
DIETARY FIBER AND VITAMIN
812
BALANCE
lnclusion of either cellulose or pectin in a fiber-free basal diet increased the rate of fecal excretion of vitamin B I2 In addifion, pectin supplements stimulated a m e - to 2 1-fold increase in urinary excretion of rnethylrnalonic acid
Key Words vitamin B12 deficiency rnethylrnalonic acid. dietary fiber cellulose pectin
The recent speculation by Burkitt et a1.l that the lack of fiber in the Western diet may contribute to the development of a variety of maladies including several gastrointestinal disorders and heart disease has provoked a vigorous and hasty response in the marketplace. With little regard for the wide range of chemical differences among the common fibers and without awaiting a systematic experimental evaluation of the valid benefits and potential hazards of supplementation. the popular outcry for "more wholesome food" has been speedily satisfied by the insertion of an assortment of fibers into many components of our daily fare. Two polysaccharides which have been included in such fiber supplements are cellulose and pectin. Cellulose is a linear polymer of Dglucose in a p-( 1 . -4) linkage. It is abundant as a plant structural polysaccharide. Pectin is also a plant polysaccharide, but its repeating unit is methyl ester galacturonic acid partially in the form of the methyl ester. Neither substance is digestible by mammalian enzymes but both may be hydrolyzed by enzymes from microorganisms in the human lower intestine. Many of the questions concerning the appropriate intake of fiber hinge upon the characteristics of the mixed microbial population which is favored or sustained by the dietary additives. Cullen and Oacez have examined the effects of cellulose or pectin supplements upon vitamin B12 metabolism in the rat. A basal B12-deficient fiber-free diet was employed 116
NUTRlTlON REVlEWS VOL. 37. NO. 4 / APRIL 1979
which consisted of 20 percent soybean protein, 70 percent glucose monohydrate, 5 percent corn oil, 0.5 percent D, L-methionine and mineral and vitamin mixes free of both cobalt and vitamin BIZ. Cellulose was added to this diet to achieve final concentrations of 10, 20, 30, 40 or 50 percent. A second series of rations contained 5, 10, 15, 20 or 30 percent of unhydrated pectin. Male 28-day-old Fischer rats were maintained on these diets in groups of six rats per treatment for ten weeks. Their growth and food intake was monitored and feces and urine were collected periodically during this time. Growth and food efficiency were reported for the first four weeks of the study. Despite the unavoidable dilution in calories, body weight gain was not affected significantly during this period in the 10 to 40 percent cellulose-diet groups. A slight decline in gain was observed for those rats fed the 50 percent cellulose ration ( 108 6 g) as compared to control animals 5 9). Since food fed the fiber-free diet (128 efficiency calculated as gain per unit of basal diet consumed was constant over the entire range, it was presumed that the difference in body weight observed in the 50 percent cellulose-consuming group was attributable to energy deficit and not to a deficiency of any essential nutrients. In contrast, food intake dropped and weight gain was progressively reduced as the proportion of dietary pectin was increased from 10 to 20 percent and the group fed 30 percent pectin lost weight. In this series, food efficiency of the fiber-free portion of the 0.004 in the diet also declined from 0.355 basal group to 0.161 L 0.029 in the 20 percent t
+
+
pectin group suggesting more serious problems than caloric dilution. Comparisons of the weight of feces and the fiber consumed indicated that little of the cellulose additive was degraded during its passage through the alimentary canal whereas most of the pectin was metabolized. In the cellulose experiment, even the lowest fiber intake per 48 hours (3.7 g) was accompanied by a significant increase in fecal weight as compared to the fiber-free ration (5.0 g vs 1.5 g, P
