Mixed micelles were prepared containing combinations of either taurocholate or taurochenodeoxycholate, monoolein, oleic acid, dioleylphosphatidylcholine (lecithin) and cholesterol. These were incubated with commercial bile-acid-sequestering resins, cholestyramine and DEAE-Sephadex, or various dietary fibers and fiber components including wheat bran, cellulose, alfalfa, lignin and 2 viscosity grades of guar gum. Binding was determined as the difference between the radioactivity of each micellar component added and that recovered in the centrifugal supernatant after incubation. In general, the extent of bile salt sequestration was characteristic and reproducible for each bile salt, and was largely unaffected by the presence of one or more additional components of the micellar mixture, including the other bile salt. Cholestyramine bound 81-92% of the bile salts and 86-99% of the phospholipid and cholesterol present in micelles. DEAE-Sephadex sequestered only 49% of the taurocholate and 84% of the taurochenodeoxycholate, but completely removed all of the phospholipid and cholesterol from micelles containing either bile salt. Among the dietary fibers, guar gum of either viscosity bound between 20-38% of each micellar component, whereas lignin, alfalfa, wheat bran and cellulose were progressively less effective in sequestration of individual components of mixed micelles. The extent of sequestration of micellar components by these resins and fibers is reasonably correlated with the effects of these same materials on lymphatic absorption of lipids and to their suggested hypocholesteremic properties.

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This report is an attempt to quantitate the observable topographical characteristics of small and large intestine after a specific dietary regimen under well-defined states of lipid absorption and metabolism. Alfalfa, white wheat bran, cellulose, and pectin were fed for 6 wk at a level of 15 g/100 g diet to four groups of rats (12 rats per dietary group). A 5th control group was maintained on Purina Rat Chow. Three animals from each group were blind-coded for morphological assessment. After anesthesia, the jejunum and mid-colon were removed and processed for scanning electron microscopy. Beginning with the mildest mucosal surface changes, the observed order in terms of increasing severity is bran less than cellulose less than pectin less than alfalfa. Our observations suggest that altered rates of cell loss in intestinal tract cytokinetics may be occurring with particular feeding patterns and should be considered as a possible mechanism in the nutritional consequences of dietary fiber intake.

Studies have been conducted on the lymphatic absorption of sitosterol (24 alpha-ethyl cholesterol), stigmasterol (delta 22, 24 alpha-ethyl cholesterol), and fucosterol (24-ethylidine cholesterol) when administered intragastrically to rats. In addition, the effect of each sterol on absorption of endogenous cholesterol has been assessed by including tracer cholesterol in the administered test emulsion. Analysis of 24-h lymph collections by GLC-mass spectrometry demonstrated that all three sterols were poorly absorbed to the extent of only 3 to 4% of the administered dose of 50 mg. In contrast, cholesterol absorption under similar conditions was about 42% of the administered dose. Administration of either sitosterol or stigmasterol resulted in an equally effective inhibition of cholesterol absorption (54%). Under identical conditions fucosterol had no effect on absorption of luminal cholesterol. The data suggest that the mechanism(s) for intestinal discrimination of sterols for absorption may be independent of the mechanism for interference with efficient cholesterol uptake by the intestine.

Rats were fed defined diets containing no fiber, 10% wheat bran or 10% cellulose, and intestinal morphology and cytokinetics were assessed by light microscopy and autoradiography, respectively. In bran-fed animals, there were no differences in morphological appearance of the jejunum, in the number of cells/villus column or in numbers of goblet cells compared to controls. Autoradiographic analysis, at one and 24 h after [3H]thymidine, however, suggested an increased turnover and villus transit of intestinal cells. There was also a 2.5 fold increase in incorporation of labeled sulfate, and a 2-fold increase in [3H]glucose incorporation into total intestinal glycoproteins and mucins. Similar, albeit less dramatic results were obtained in rats fed diets containing cellulose. These studies provide evidence that diets containing certain fiber derivatives can alter aspects of intestinal cell turnover, and support the earlier morphological observations suggesting increased goblet cell secretory activity in response to feeding these fiber derivatives.

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Adult male rats fed defined diets containing various fiber supplements or cholestyramine for 4 wk were surgically provided with lymphatic drainage catheters and starved overnight. After duodenal administration of a standard lipid test emulsion, absorption rates and lipoprotein distributions of cholesterol and oleic acid were determined. Prefeeding diets containing cellulose or alfalfa had no significant effect on oleic acid absorption. Diets containing pectin, guar gum, metamucil, mixed fibers (Fibyrax), or cholestyramine caused decreased lymphatic recovery in the initial period; except for the metamucil diet, no decrease was caused in the 24-h recovery, suggesting delayed but not impaired absorption. Fatty acid distribution among lipoproteins and chylomicron size were not altered by diet. All supplements caused a significant reduction in cholesterol absorption during the initial period, and cholesterol absorption remained depressed in animals prefed pectin, guar gum, mixed fibers, metamucil, and cholestyramine.