Effect of a very-high-fiber vegetable, fruit, and nut diet on serum lipids and colonic function.

We tested the effects of feeding a diet very high in fiber from fruit and vegetables. The levels fed were those, which had originally inspired the dietary fiber hypothesis related to colon cancer and heart disease prevention and also may have been eaten early in human evolution. Ten healthy volunteers each took 3 metabolic diets of 2 weeks duration. The diets were: high-vegetable, fruit, and nut (very-high-fiber, 55 g/1,000 kcal); starch-based containing cereals and legumes (early agricultural diet); or low-fat (contemporary therapeutic diet). All diets were intended to be weight-maintaining (mean intake, 2,577 kcal/d). Compared with the starch-based and low-fat diets, the high-fiber vegetable diet resulted in the largest reduction in low-density lipoprotein (LDL) cholesterol (33% +/- 4%, P <.001) and the greatest fecal bile acid output (1.13 +/- 0.30 g/d, P =.002), fecal bulk (906 +/- 130 g/d, P <.001), and fecal short-chain fatty acid outputs (78 +/- 13 mmol/d, P <.001). Nevertheless, due to the increase in fecal bulk, the actual concentrations of fecal bile acids were lowest on the vegetable diet (1.2 mg/g wet weight, P =.002). Maximum lipid reductions occurred within 1 week. Urinary mevalonic acid excretion increased (P =.036) on the high-vegetable diet reflecting large fecal steroid losses. We conclude that very high-vegetable fiber intakes reduce risk factors for cardiovascular disease and possibly colon cancer. Vegetable and fruit fibers therefore warrant further detailed investigation.

Dietary psyllium increases expression of ileal apical sodium-dependent bile acid transporter mRNA coordinately with dose-responsive changes in bile acid metabolism in rats.

Psyllium (PSY), a type of dietary fiber containing mainly soluble components, has been shown to decrease serum cholesterol concentrations in several species; however, mechanisms involved are not clearly defined. Four groups of 10 rats were fed semipurified diets containing 10% dietary fiber from cellulose and/or PSY for 21 d. Increasing levels of PSY were fed (0,3.33, 6.67 and 10% PSY) with the remaining 10% made up with cellulose. Liver cholesterol, cholesterol 7alpha-hydroxylase (CYP7A) activity and mRNA, 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) mRNA, ileal apical sodium-dependent bile acid transporter (ASBT) mRNA, fecal bile acids and total steroids, and intestinal bile acid content were measured. All variables responded in a dose-dependent manner to PSY in the diet. Total liver cholesterol content was significantly reduced in all groups fed PSY compared to cellulose-fed controls [138(a), 105(b), 105(b) and 93(c) micromol (SEM = 4.2) for 0, 3.33, 6.67 and 10% PSY, respectively]. Activity of CYP7A was significantly greater in all groups fed PSY compared to the cellulose-fed controls [6.36(c), 16.92(b), 15.28(b) and 20.37(a) pmol x min(-1) x mg protein(-1) (SEM = 3.19) for 0, 3.33, 6.67 and 10% PSY, respectively]. These differences in CYP7A activity were similar to differences in CYP7A, HMGR and ASBT mRNA levels. Fecal bile acid and total steroid excretion as well as total intestinal bile acids were significantly greater in rats fed PSY-containing diets compared to 0% PSY-fed rats. These results suggest that the reduction in liver cholesterol involves modulating the size and composition of the bile acid pool via regulation of ileal ASBT, CYP7A and HMGR mRNA levels.

Dietary psyllium increases fecal bile acid excretion, total steroid excretion and bile acid biosynthesis in rats.

Psyllium, a source of dietary fiber rich in soluble components results in lower serum cholesterol concentration in several species. Suggested mechanisms for the hypocholesterolemic effect include a greater excretion of fecal bile acids and total steroids, and up-regulation of bile acid biosynthesis. The activity of cholesterol 7alpha-hydroxylase (7alphaOHase), the rate limiting enzyme in bile acid biosynthesis, is higher in rats fed 5% psyllium. Whether this higher activity corresponds to an increase in mRNA levels has not been determined. Four groups of 10 rats were fed a semipurified diet containing 5% cellulose (CEL; control), 5% cellulose plus 1% cholic acid (CCA), 5% cellulose plus 2% cholestyramine (CHY) or 5% psyllium hydrocolloid (PSY) for 3 wk. Liver cholesterol concentration, fecal bile acid and total steroid excretion, 7alphaOHase activity and 7alphaOHase mRNA levels were measured. Liver cholesterol content in rats fed CCA was significantly higher than in all other groups. Rats fed CHY and PSY had significantly lower liver cholesterol content than those fed CEL. Total fecal steroid and bile acid excretions were significantly greater in rats fed CCA, CHY and PSY than in those fed CEL. Activities and mRNA levels of 7alphaOHase in rats fed CHY and PSY were significantly higher than in rats fed CEL or CCA. These data indicate that feeding psyllium to rats increases fecal bile acid and total steroid excretion as well as 7alphaOHase activity and 7alphaOHase mRNA levels.

Long-term effect of soluble-fiber foods on postprandial fat metabolism in dyslipidemic subjects with apo E3 and apo E4 genotypes.

To determine the long-term effect of soluble fiber on postprandial fat metabolism, we studied 33 dyslipidemic subjects, 16 with apolipoprotein (apo) E3/3 (E3) and 17 with E3/4 or E4/4 (E4) genotypes. They ate preweighed low-fat (20% of energy), high-fiber (> 5.7 g/MJ) diets for two 4-mo periods separated by a 2-mo washout period according to a randomized, crossover design. One diet contained foods rich in insoluble fiber and the other foods rich in soluble fiber. On 1 d during the last 2 wk of each diet, subjects ingested a standard, fiber-free, fatty liquid meal containing retinyl palmitate as a marker of intestinally derived lipoproteins. Plasma samples were obtained at hourly intervals for 10 h. Compared with the insoluble-fiber diet, soluble fiber reduced fasting plasma total cholesterol in both E3 (6.6 +/- 2.1%, P = 0.007)and E4 subjects (5.6 +/- 2.1%, P = 0.017). Soluble fiber increased fecal total bile acid output in both E3 (76 +/- 18%, P < 0.001) and E4 subjects (85 +/- 19%, P < 0.001). The incremental area under the chylomicron triacylglycerol response curve was significantly greater after soluble fiber than after insoluble fiber in E3 (3.56 +/- 0.56 compared with 2.87 +/- 0.38 mmol x h/L, respectively, P = 0.046) but not in E4 subjects (5.19 +/- 0.78 compared with 4.92 +/- 0.81 mmol x h/L). Kinetic analysis suggested an increase in retinyl palmitate absorption in E3 subjects after soluble fiber, but no difference in E4 subjects. These results suggest that a long-term increase in dietary soluble fiber has no effect on postprandial fat metabolism in subjects with an apo E3/4 or E4/4 genotype. However, soluble fiber enhances apparent fat absorption in E3 subjects, which could be due to an increased bile acid pool and increased micelle formation.

Bile acid analysis: methods and problems.

What is the ideal method for analysis of faecal bile acids? Selection of an ideal system for a specific situation requires consideration of several factors, eg the information sought, availability of equipment and time constraints. Each laboratory will select procedures based on these constraints. A situation in which a large number of subjects are to be screened for total bile acid concentration might suggest use of single-day collections, lyophilization prior to homogenization, extraction using the Evrard and Janssen method and quantification by 3 alpha-hydroxysteroid dehydrogenase. However if the ratio of glycine to taurine conjugates and the daily excretion were of interest, separation of subclasses with Lipidex 1000 followed by both gas chromatography (of free bile acids) and HPLC (of conjugated bile acids) would be selected. There is not a best method for all situations. What does the future hold for improving this methodology in order to improve our ability to use faecal bile acid analysis clinically? The biggest problem facing the application of faecal bile acid analysis to clinical situations in the lack of ability to devise a rapid method (24-48 h) which retains the accuracy of current methods. One promising development is the potential application of immunological methods to faecal bile acids. These detection methods have been applied primarily to serum to date but if extraction and/or purification methods could be coupled with this method of quantification, a clinically acceptable method may result.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of increasing levels of hard wheat fiber on fecal weight, minerals and steroids and gastrointestinal transit time in healthy young women.

Hard red wheat bran (HRWB) baked in a yeast-leavened bread was fed to 36 healthy young college women consuming a basal diet of traditional foods, which contained 15 +/- 3 g/d dietary fiber (DF). Three levels of HRWB were added supplying, respectively, 5.7, 17.1 and 28.5 g/d DF; an additional treatment group did not receive any HRWB. Fecal collections were carried out in the last 5 d of treatment. Fecal wet weight, fecal dry weight and fecal ash increased significantly for each increase in HRWB (P less than 0.05). Fecal dry matter percent changed significantly only at the highest level of HRWB (P less than 0.05). After accounting for the minerals in the HRWB, there was an increased fecal loss of Ca, but not of Zn, Cu, Fe or Mg compared to the women fed no HRWB. HRWB at a level of 17.2 g/d induced faster transit times (TT) than no HRWB and 66 g/d HRWB induced faster TT than either 17.2 or 39.6 g/d HRWB (P less than 0.05). Total daily fecal steroids were not altered by changes in HRWB. Daily total bile acid excretion increased significantly (P less than 0.05) at the two higher levels of HRWB due primarily to higher excretion of chenodeoxycholic acid.

Comparison of two lighting regimens and drinker cleaning programmes on the performance and incidence of leg abnormalities in turkey males.

Turkey males subjected to a low intensity step-down (LISD) lighting programme showed significantly heavier body weights after 20 weeks of age and significantly better feed conversions after 14 weeks of age compared with males reared in a high intensity step-up lighting (HISU) programme. Although both nonchilled and chilled carcase weights were higher, the dressing percentages were lower for males of the LISD lighting regimen. Males of the HISU lighting programme had significantly fewer leg abnormalities, shorter tarso-metatarsi, lighter drumstick weights, and lighter tibia weights. Males on the HISU lighting programme from 15 to 19 weeks of age had larger testes; however, after 20 weeks of age they were larger in males on the LISD lighting regimen. Cleaning and disinfecting the drinking troughs daily rather than weekly had no effect on any production variable measured.