Effects of a standardized wheat bran preparation on biliary lipid composition and bile acid metabolism in young healthy males

Laxative effects of wheat bran and psyllium: Resolving enduring misconceptions about fiber in treatment guidelines for chronic idiopathic constipation

BACKGROUND

Treatment guidelines for chronic idiopathic constipation (CIC) recommend an "increase in fiber intake" as a first-line therapy, but most epidemiologic studies fail to support an association between a high-fiber diet and a reduced risk of constipation. Furthermore, randomized controlled clinical studies show that most isolated fibers (e.g., supplements) are not different from placebo for a laxative effect, and several may be constipating.

OBJECTIVES

The objective of this review was to compare the effects of two isolated fibers, coarse wheat bran and psyllium, on stool output and stool water content in patients with CIC. This review will also address misconceptions about fiber that are perpetuated by treatment guidelines.

DATA SOURCES

A comprehensive literature review was conducted with the use of the Scopus, SciFinder, and PubMed scientific databases, limited to the previous 50 years (1968-2018; latest date included, December 31, 2018).

CONCLUSIONS

In patients with CIC, nonfermented gel-forming psyllium was 3.4 times more effective than insoluble wheat bran for increasing stool output. Both psyllium and coarse wheat bran increased stool water content, a stool-softening effect, but finely ground wheat bran decreased stool water content, a stool-hardening effect.

IMPLICATIONS FOR PRACTICE

It is a misconception that dietary fiber and all isolated fibers provide a laxative effect in patients with CIC. Our analysis suggests that treatment guidelines for CIC should make specific evidence-based recommendations as it pertains to fiber. To do otherwise takes the risk of perpetuating myth and misunderstanding and depriving patients of an effective therapy for CIC. A generic recommendation to "increase fiber intake" is akin to a recommendation to "increase pill intake" without regard to therapeutic or adverse effects.

Effect of lactulose and fiber-rich diets on bile in relation to gallstone disease: an update

The primum movens in cholesterol gallstone formation is hepatic cholesterol hypersecretion and chronic supersaturation of bile. From this event a cascade of contributing factors can be differentiated: (i) Motility defects with impaired gallbladder contractility and gallbladder stasis, but also with small and large intestinal hypomotility. (ii) Multiple biochemical defects in gallbladder bile with increased biliary proteins, increased deoxycholic acid and rapid crystallization of biliary cholesterol from supersaturated unstable vesicles. There is considerable evidence that slow intestinal and colonic transit can increase the deoxycholic acid pool size and biliary cholesterol saturation. Changes in intestinal transit influence the anaerobic bacterial enzymatic biotransformation of conjugated cholate to more hydrophobic deoxycholate. This leads to biliary cholesterol hypersecretion and gallstone formation. Prokinetic drugs or administration of lactulose or fiber products like bran can change the slow intestinal transit favourably with subsequent reduction in deoxycholic acid formation and cholesterol saturation of bile. Whether these applications are indeed of value in the long-term prevention of gallstone disease, however, is doubtful, since fiber-rich diet in prevention of gallstone recurrence after complete gallstone dissolution was not successful.

Binding of bile salts to fibre-enriched wheat fibre

A commercial product of fibre-enriched wheat fibre (Fiberform R) was tested for its binding of bile salts in vitro. The wheat fibre preparation was standardized and through enzymatic digestion of protein and starch contained 78 per cent fibre (w/w). Fibre-enriched wheat fibre bound with high capacity both conjugated and unconjugated bile salts. Binding was saturable, reversible and showed no specificity towards tauro- or glycine-conjugated bile salts. Binding was rapid, dependent on pH, was enhanced by the presence of high salt concentrations and partially inhibited by 6 M urea. This indicated that binding was a combination of hydrophobic and hydrophilic interactions.

Influence of increased fibre intake on biliary lipids

Influence of increased fibre intake on biliary lipids. The influence of dietary fibres (30 g wheat bran per day) on the lithogenicity of the bile was studied in ten healthy persons, whose body weight was 76.8 +/- 2.3 kg, height 189.9 +/- 2.1 cm, age 25.5 +/- 0.26 years. These 10 young male volunteers were given twice daily 15 g wheat bran additionally for six weeks in addition to their normal diet. The bile was obtained endoscopically prepapillarily following stimulation of the gallbladder with ceruletid. The contraction of the gallbladder was controlled sonographically. Increased dietary fibre intake resulted in significant lowering of cholesterol concentration in the bile from 3.27 +/- 0.89 mmol/1 to 2.50 +/- 0.67 mmol/1. The lithogenic index (Admirand and Small, 1968) decreased statistically significant from 1.01 +/- 0.14 to 0.67 +/- 0.11. Total cholesterol and HDL and LDL cholesterol remained unchanged; likewise, there was no change in serum triglyceride and phospholipid concentrations. Hence, an increased intake of dietary fibres of the wheat bran type should be the first dietary measure in both prevention and treatment of cholesterol gallstone disease.

In vivo studies with fibre components

There are few studies in man examining the in vivo effects of dietary fibre on bile acid metabolism but divergent results have been recorded depending on the amount and type of fibre eaten. Studies in which the fibre components pectin, cellulose, and lignin were fed to normal volunteers for four weeks have been reported. The highly fermentable component pectin is associated with increased secondary bile acid formation in contrast to the partially fermentable component cellulose in which the opposite occurs. Lignin has no effect on bile acid metabolism. No component significantly alters biliary lipids. Since ordinary diets contain a mixture of different fibres the net effect will depend on the relative amounts of each. Significant changes in bile acid metabolism and biliary lipids in the longer term (greater than 4 weeks) however, are not precluded by the results of these short term studies.

Effects of a new, concentrated wheat fibre preparation on intestinal transit, deoxycholic acid metabolism and the composition of bile

When the cholesterol saturation index of bile is reduced by wheat bran there is generally a fall in the deoxycholic acid content of bile. As the same effects occur with senna, bran might act on bile simply via its accelerating effect on colonic transit. We have studied the effects of a new, concentrated, wheat fibre preparation (Testa Triticum Tricum, Trifyba, which is 80% dietary fibre) upon bile composition, deoxycholic acid metabolism and intestinal transit time, and have assessed whether these effects are related. Twenty constipated volunteers were prescribed Testa Triticum Tricum in doses (10-32 g/day) sufficient to relieve their symptoms for at least six weeks. Before and at the end of this period, duodenal bile was sampled to enable measurement of deoxycholic acid pool (by isotope dilution), total bile acid pool, bile acid composition and cholesterol saturation index. Whole gut transit time fell from 120 +/- SD35 to 68 +/- 35 hours. At the same time, biliary % deoxycholic acid fell from 26.6 +/- 12.0 to 23.0 +/- 11.8 (p = 0.002), the total bile acid pool expanded from 2.36 +/- 0.88 to 2.75 +/- 0.90 g (p = 0.008) and cholesterol saturation index fell from 1.13 +/- 0.32 to 1.07 +/- 0.29 (p = 0.04). In subjects with initial cholesterol saturation index over 1.0 (n = 12), it fell from 1.33 +/- 0.25 to 1.22 +/- 0.21 (p = 0.008). There was no significant correlation between change in saturation index and change in % deoxycholic acid or deoxycholic acid pool, nor between any of these parameters and change in transit time. Testa Triticum Tricum reduces the cholesterol saturation index of supersaturated bile but this action appears to be independent of its effect on colonic transit and of changes in deoxycholic acid metabolism.

Effects of the fibre components pectin, cellulose, and lignin on bile salt metabolism and biliary lipid composition in man

Randomised crossover studies in three separate groups of 10 healthy volunteers were undertaken to determine the effects of biliary lipid composition and bile salt metabolism of daily dietary supplementation for four weeks with the purified fibre components pectin (12 g/day), cellulose (15 g/day) and lignin (12 g/day). The subjects' biles were initially unsaturated with cholesterol and no significant changes in the lithogenic indices or mean percentages of cholesterol, phospholipid, or total bile acids after any of the supplements were observed. After pectin, the mean (+/- SD) percentage of cholic acid decreased significantly from 42.8 (+/- 10.8) to 39.0 (+/- 11.2), the mean (+/- SD) percentage of deoxycholic acid increased significantly from 18.2 (+/- 13.7) to 25.4 (+/- 13.5) and C14-deoxycholate metabolites were raised significantly by 65%. After cellulose, the mean (+/- SD) percentage of chenodeoxycholic acid was increased significantly from 33.6 (+/- 6.3) to 35.4 (+/- 7.0), the mean (+/- SD) percentage of deoxycholic acid decreased significantly from 18.6 (+/- 9.6) to 14.2 (+/- 8.3) and C14-deoxycholate metabolites halved. Lignin did not exert any significant effects. Though these results show that individual fibre components are associated with quite different effects on bile acid metabolism, in the short term no significant effect on biliary cholesterol saturation was observed in bile initially unsaturated with cholesterol. The bile acid changes most likely result from the different effects on colonic metabolism induced by the individual fibre components.

Metabolic effects of dietary fiber from dehulled soybeans in humans

The normal diet of six healthy volunteers was supplemented by 21 g of dietary fiber from two different soybean seed fiber preparations, either a nonpurified and never-dried soya pulp A (39% dietary fiber) or a purified soya fiber B (79%), for 3 wk each. Mean daily fecal wet weight was increased by 19 and 38% in the fiber periods A and B as compared to a 2-wk control period (p less than 0.05). Stool frequency and transit time remained unchanged. Fecal fiber increased by 52% only during period B. Fecal calcium, magnesium, and iron were increased (p less than 0.05), mainly after higher intakes during both fiber periods. Excretion of neutral steroids remained unchanged, but their concentration was lowered (p less than 0.05). A 21% increase of fecal bile acids by fiber A was specifically due to deoxycholic acid (+32%, p less than 0.01). Oral glucose tolerance was slightly improved after period B. Neither fiber changed serum triglycerides, but fiber B increased low-density lipoprotein-cholesterol by 19% (p less than 0.01) and low-density lipoprotein-phospholipids by 16% (p less than 0.05). The ratio high-density/low-density lipoprotein-cholesterol, however, did not change significantly. Thus, dietary fibers from soybean do not seem to contribute to the hypocholesterolemic effect of soya. The results of this study also demonstrate that two apparently similar dietary fibers, coming from a single source, can exert distinctly different metabolic effects.

Measurement of bile acid kinetics in human serum using stable isotope labeled chenodeoxycholic acid and capillary gas chromatography electron impact mass spectrometry

A non invasive method for measurement of bile acid kinetics in serum using (24-13C)chenodeoxycholic acid has been developed. After oral administration of 50 mg (24-13C)chenodeoxycholic acid, the exponential decay of the 13C atom percent excess was measured in serum using capillary gas chromatography mass spectrometry. This required that isotope ratios were measured with high accuracy and coefficients of variation less than 1% by means of selected ion monitoring and scan averaging. The clinical applicability was tested by repeated determination of pool size, fractional turnover and synthesis rate of chenodeoxycholic acid in one healthy volunteer. This method permitted the determination of pool size, synthesis and conversion of chenodeoxycholic acid into lithocholic acid in man without the use of radioactive tracers and without repeated duodenal intubation.