Effect of two kinds of pectin and guar gum on 1,2-dimethylhydrazine initiation of colon tumors and on fecal beta-glucuronidase activity in the rat.

The effect of 5% low-methoxylated pectin, high-methoxylated pectin, and guar gum on 1,2-dimethylhydrazine initiation of colon cancer was investigated using groups of 30 rats. The growth of the rats in the different groups was very similar to that of control group fed a fiber-free diet. Both kinds of pectin increased the multiplicity of color tumors, whereas guar gum did not significantly influence carcinogenesis. Bacterial beta-glucuronidase activity in feces and colonic content was the same in pectin-fed rats and controls but significantly lower in the guar gum group. Thus, it was not related to the number of tumors in each group.

Effect of dietary fiber on the induction of colorectal tumors and fecal beta-glucuronidase activity in the rat.

The purpose of the present study was to investigate whether three different types of dietary fiber, wheat bran, carrot fiber, and citrus pectin, influenced the induction of colorectal tumors produced by 1,2-dimethylhydrazine in rats. In all groups, the tumor yield was high (87 to 97%). In the wheat bran and carrot fiber groups, the incidence of colorectal tumors was not significantly different from that of the group fed on the fiber-free basic diet. The citrus pectin group, however, had a significantly higher incidence of colorectal tumors (p less than 0.001). An increased number of auditory duct tumors was also noted in this group. In a separate experiment, dietary pectin induced a 10-fold increase in fecal beta-glucuronidase activity but did not alter this activity in the bowel wall. It has been suggested that dietary fiber protects against the induction of colorectal tumors, but this was not the case in the experiment. It is possible that the high tumor yield made the demonstration of a weak protective effect of wheat bran impossible. The reason for the increased occurrence of tumors in the citrus pectin group is obscure and will be subjected to further investigation. Fecal beta-glucuronidase activity might be one factor of importance in the activation of the carcinogen.

Dietary fibre--definition, chemistry and analytical determination.

Dietary fibre includes non-starch polysaccharides and lignin that are not digested or absorbed in the human small intestine. It contains a mixture of chemically complex polysaccharides. Lignin is a highly cross-linked complex polymer of phenylpropane units. The plant cell wall is the main source of dietary fibre and its structure is reviewed briefly. The structure of the main dietary fibre polysaccharides is then summarized. The demarcation between starch--the main digestible polysaccharide--and dietary fibre presents some problems due to more or less enzyme resistant starch fractions that occur naturally or are formed with processing. "Resistant starch" formed during baking passes through the small intestine in the rat and, probably, in man and is fermented in the colon. It should therefore also be regarded as dietary fibre. Methods for dietary fibre determination fall into two categories: gravimetric methods, weighing the dietary fibre after removal of other components; component analysis methods, determining monomeric composition of fibre polysaccharides (preferably by gas-liquid chromatography) supplemented with a gravimetric lignin determination and separate assay of uronic acid components (pectin). Recently developed enzymatic gravimetric methods are most convenient for the assay of total dietary fibre or water soluble and insoluble fibre separately, whereas component analysis is required for determining the dietary fibre composition.

Human small-intestinal -galactosidases. Separation and characterization of three forms of an acid -galactosidase.

1. An acid beta-galactosidase, optimum pH4.0-4.5, in the human small-intestinal mucosa was separated and characterized. 2. Autolysis of mucosal homogenates at acid pH inactivated the lactase and hetero beta-galactosidase; the total activity of the acid beta-galactosidase was only slightly depleted, but a greater proportion of the enzyme was solubilized by this treatment. 3. Separation on a Sephadex G-200 column revealed that the acid beta-galactosidase could occur in at least three different forms, probably representing monomer, dimer and octamer or polymer of the enzyme. 4. The properties of the different forms of the acid beta-galactosidase were studied with regard to pH optimum, K(m), rate of hydrolysis of different substrates, and sensitivity to p-chloromercuribenzoate and tris as inhibitors. All these properties were the same for the different forms of the enzyme. 5. The acid beta-galactosidase hydrolyses lactose as well as hetero beta-galactosides and contributes to the lactase activity of intestinal biopsies also when measured at pH 6. This enzyme may therefore be responsible for a considerable part of the residual lactase activity found in lactose-intolerant patients.

Effect of oat saponins on plasma and liver lipids in gerbils (Meriones unguiculatus) and rats.

The effects of oat saponins (a mixture of avenacosides A and B) on plasma and liver lipids in gerbils (Meriones unguiculatus) and rats were investigated. Cholesterol-containing diets high in total and saturated fat and with different avenacoside contents (zero (ethanol-extracted oats), normal (oats) and twice normal (ethanol-extracted oats plus added avenacosides)) were used. Compared with a cellulose control group the oat diets in both species gave a significantly higher cholesterol content in the HDL fraction and a significantly lower liver cholesterol content. No significant differences in total plasma cholesterol, HDL-cholesterol and plasma triacylglycerols were found, however, between the groups fed on oats with different avenacoside content. The liver weight, total liver cholesterol and free liver cholesterol were also similar, whereas the liver lipid content was significantly lower in rats given the highest amount of avenacosides compared with zero or normal amounts. The tendency was the same in gerbils. Thus, the oat saponins had only minor effects on lipid metabolism in gerbils and rats.

Fermentation of dietary fibre in the intestinal tract: comparison between man and rat.

1. The breakdown and faecal bulking capacity of dietary fibre preparations from wheat bran, apple, cabbage, carrot, and guar gum were compared in man and rat. 2. The degradation of the fibre showed good correlation between man and rat (r 0.99, regression coefficient 0.86). Wheat bran was the least well-digested, 66 and 59% of the neutral sugars being excreted in faeces of man and rat respectively. The breakdown of the fibre in apple, cabbage, carrot and guar gum was more complete and 4-29% of the neutral sugars were recovered in faeces. 3. The main dietary fibre constituents in each preparation were degraded to a similar extent in man and rat. The main dietary fibre constituents of apple, carrot, cabbage and guar gum were almost completely degraded. Of the xylose in wheat bran 45% (man) and 48% (rat) were recovered in faeces. However, the percentage excretion of glucose and arabinose from bran was higher in man. 4. A faecal glucan other than cellulose was identified in human faeces after guar gum, and has been provisionally identified as starch. No such glucan occurred in rat faeces. 5. A good correlation between the faecal bulking capacity in man and rat was seen (r 0.97, regression coefficient 0.56). Wheat bran had the best bulking capacity, while that of apple, cabbage, carrot and guar gum was less pronounced. Faecal bulking was inversely related to the amount of fibre which was water-soluble in each preparation. 6. It is concluded that this rat experimental model is useful for the prediction of fermentative breakdown and bulking capacity of dietary fibre in man. However, more comparative studies are needed to evaluate animal experiments regarding other physiological effects of dietary fibre.