Influence of dietary fiber on bile acid metabolism

Fiber, when fed to animals or man, will generally cause increased excretion of bile acids. The level of bile acid excretion appears to be a function of the structure of the fiber. Fiber binds bile acids and bile salts in vitro. The extent of binding is characteristic for each type of fiber and each substrate. Bile acid binding may be one mechanism of the physiological action of fiber.     

Psyllium, not pectin or guar gum, alters lipoprotein and biliary bile acid composition and fecal sterol excretion in the hamster

Different soluble dietary fibers known to alter cholesterol metabolism were fed to golden Syrian hamsters, and their specific impact on lipoproteins, biliary bile acid profile, and fecal sterol excretion was evaluated. Semipurified diets containing 20% fat; 0.12% cholesterol; and 8% of psyllium (PSY); high (hePE) and low (lePE) esterified pectin; or high (hvGG) and low (lvGG) viscous guar gum were fed for 5 wk. Compared to control, PSY caused a significant reduction in plasma cholesterol (2.9±0.5 vs. 5.5±0.5 mmol/L), whereas hePE, lePE, hvGG, or lvGG had no apparent effect on plasma lipids. Hepatic total and esterified cholesterol were substantially decreased with PSY, pectin and guar gum, whereby PSY produced the most pronounced effect. Distinctive changes existed in the bile acid profile related to the different fibers. In contrast to pectin and guar gum, PSY caused a significant increase in the cholate:chenodeoxycholate and the glycine:taurine conjugation ratio. Pectin and guar gum did not alter daily fecal neutral sterol excretion while PSY caused a 90% increase due to a higher fecal output. Daily fecal bile acid excretion and total fecal bile acid concentration were significantly increased by PSY, whereas hePE, lePE, hvGG, and lvGG revealed no or only minor effects. Taken together, the disparate hypocholesterolemic effects of PSY, pectin, and guar gum on cholesterol and bile acid metabolism in the hamster are possibly related to different physicochemical properties, e.g., viscosity and susceptibility to fermentation, affecting the fiber-mediated action in the intestine.     

Dietary fiber supplements: Effects on serum and liver lipids and on liver phospholipid composition in rats

Rats (6 per group) were fed semipurified diets containing either particulate fibers (alfalfa, 10%; cellulose, 10%; bran, 10%), a soluble ionic fiber (pectin 5%), soluble, nonionic fibers (guar gum, 5%; Metamucil, 10%), a mixed fiber preparation (Fibyrax, 10%, or an insoluble, ionic bile acid-binding resin (cholestyramine, 2%). The control group was fed the unsupplemented diet. The feeding period, during which diet and water were provided ad libitum, was 28 days. Compared with the control group, serum total cholesterol levels were increased by more than 10% in rats fed alfalfa and decreased by more than 10% in rats fed cellulose, guar gum, Fibyrax and cholestyramine. There were no significant differences in percentage of plasma HDL cholesterol. Serum triglycerides were elevated in the groups fed alfalfa, pectin, guar gum or Fibyrax and reduced in the group fed Metamucil. Plasma phospholipids were elevated in rats fed alfalfa or bran, unaffected in rats fed pectin or Metamucil and reduced in the other groups. Liver total cholesterol was elevated in all groups but those fed wheat bran and cholestyramine. The percentage of liver cholesterol present as ester was elevated in every group except that fed cholestyramine. Liver triglycerides were reduced in rats fed guar gum or Metamucil and elevated in those fed alfalfa. Liver phospho-lipids were lowered in the group fed cellulose. Liver phospholipids were fractionated by thin layer chromatography to give phosphatidylcholine (PC), phosphatidylethanolamine (PE), sphingomyelin (Sph), lysophosphatidylcholine (LPC) and phosphatidylinositol plus phosphatidylserine (PI+PS). PC was elevated in all test groups (7–25%); PE levels ranged from 14% below to 0.3% above controls; Sph levels were sharply lower (20–53%) in all groups. LPC and PI+PS levels were close to the control value in all test groups. The results demonstrate that different dietary fibers can affect liver phospholipid composition. In view of the critical roles of phospholipids in many biological reactions, it will be interesting to survey the influence of dietary fiber on phospholipid spectra of other tissues. Deceased.     

Effects of a diet high in plant sterols,vegetable proteins,and viscous fibers (dietary portfolio) on circulating sterol levels and red cell fragility in hypercholesterolemic subjects

Plant sterols, soy proteins, viscous fibers, and nuts are advised for cholesterol reduction, but their combined effect on plant sterol absorption has never been tested. We assessed their combined action on serum sterols in hyperlipidemic subjects who were following low-saturated fat diets before starting the study and who returned to these diets post-test. The 1-mon test (combination) diet was high in plant sterols (1 g/1,000 kcal), soy protein (23 g/1,000 kcal), viscous fiber (9 g/1,000 kcal), and almonds (14 g/1000 kcal). Fasting blood was obtained for serum lipids and sterols, and erythrocytes were obtained for fragility prior to and at 2-wk intervals during the study. The combination diet raised serum campesterol concentrations by 50% and β-sitosterol by 27%, although these changes were not significant after Bonferroni correction; near-maximal rises were found by the end of the first week, but no change was found in red cell fragility despite a 29% reduction in the LDL cholesterol level. No significant associations were observed between changes in red cell fragility and blood lipids or sterols. We conclude that plant sterols had a minimal impact on serum sterol concentrations or red cell fragility in hyperlipidemic subjects on diets that greatly reduced their serum lipids.     

A high-saturated fat diet enriched with phytosterol and pectin affects the fatty acid profile in guinea pigs

This paper presents the results of a study whose aim was to test the effects of several doses of pectin and phytosterols on the body weight gain and the FA content in emale guinea pigs. The treatments resulted from supplementing with pectin and plant sterol a guinea pig diet (rich in saturated FA), following a 3×3 factorial design, with three levels of pectin (0,3.67 and 6.93%) and three levels of phytosterols (0, 1.37, and 2.45%). Seventy-two female Dunkin Hartley guinea pigs were randomly assigned to the treatment groups (8 animals/group), the duration of the treatment being 4 wk. Pectin dietary intake led to a significant increase in body weight (P<0.001), food consumption (P=0.025), and feed efficiency (P<0.001), but no influence of phytosterols on weight gain or food consumption was detected. We found a significant negative effect of the addition of phytosterols on lauric, myristic, and palmitic acid concents in feces, and a positive effect on their concentration in plasma and liver, but no significant effect on stearic acid content. Apparent FA absorption was assessed by calculating the ratio of FA in feces and diets that the absorption of the different FA could be compared, and the negative effect of phytosterol supplementation on these ratios, especially for lauric and myristic acids, was established.     

海藻膳食纤维制取、特性及功能活化研究进展

海藻不但能净化养殖水质,还含有丰富的藻胶、纤维素、半纤维素、维生素和矿物质等,是生产膳食纤维的优质原料,膳食纤维对人类健康有积极的作用,在预防人体胃肠道疾病和维护胃肠道健康方面功能突出,利用好这些藻类,是环保与增收双赢的好方法。文章综合叙述了一些藻类加工膳食纤维的方法及发展趋势以及海藻膳食纤维的理化特性、安全性等。     

Effects of soya protein on mineral Availability

Conclusions There is no evidence that soy protein per se directly affects the bioavailability of minerals. Most researchers believe that soybean protein in soybean products plays a casual role in reduced bioavailability of minerals from soya. The bioavailability of mineral, particularly zinc, may decline during the processing of soya products by the formation of protein-phytic acid-mineral complexes. These complexes seem to form more readily at pH from 7 up to 8 or 10, especially in the presence of high amounts of dietary calcium. Neutralized soya protein concentrates and isolates have been shown to have relatively low zinc bioavailability for rats as compared to other soy products. Experimental evidence based upon work with the rat and chick demonstrate a highly variable bioavailability of minerals, especially zinc. Unit food processing procedures can greatly modify zinc utilization for these experimental animals. These results do not necessarily predict how man will utilize minerals from soya products. Thus far, a few published studies of humans raise hopes that man can utilize soy products in mixed diets without alterations in mineral metabolism. Considerably more basic research is needed to determine the bioavailability of minerals from soya for man and, if necessary, to develop economically feasible processing procedures that optimize recovery and functionality of soya protein, yet reduce the amount or effect of phytic acid on mineral bioavailability. The alternative action is prudent fortification of soya protein products. Fortification should be undertaken when the product has the potential or making a significant contribution to the human diet. Indiscriminate fortification is to be avoided; this could lead to induction of alternate mineral deficiencies. For example, calcium addition to diets containing phytate reduces zinc utilization, whereas zinc addition may reduce copper utilization.     

Development,physical-chemical properties,and photodegradation of pectin film reinforced with malt bagasse fibers by continuous casting

This work aims to develop composite films from renewable sources and to use a residue from the brewing industry, malt bagasse, as a reinforcing agent. The composites were prepared with 0–15 wt%/wt% of malt bagasse, using the continuous casting process. All films were characterized in terms of their microstructure, physicochemical, mechanical, and photodegradation properties. The properties of the films were influenced by the concentration variation of the malt bagasse fiber, allowing the deformation of the films to increase by approximately 57%. The incorporation of 15 wt%/wt% of malt bagasse provided a reduction in the water vapor transmission rate and in the hygroscopicity of the pectin films. However, the fibers acted as UV light blockers, making it difficult to photodegradate the films. Therefore, the composite films based on pectin and malt bagasse presented adequate properties to be used in the packaging industry.     

Effects of low casein and fish oil on hyperlipidemia and proteinuria in nephritic rats

The effects of amino acid-fortified low casein and fish oil (FO) diets on hyperlipidemia and proteinuria were studied in rats with nephrotoxic serum nephritis. After an antiserum injection, rats were maintained for 14 d on four different experimental diets: a 20% casein diet containing corn oil (CO) or FO, or an 8% casein diet supplemented with cystine plus threonine containing CO or FO. The 8% casein diets reduced urinary protein excretion in nephritic rats without inducing severe growth retardation or fatty liver compared with the basal 20% casein diets. Both the 8% casein diet and the FO diet decreased serum cholesterol, triglyceride and phospholipid levels in nephritic rats, and nonesterified fatty acid levels were decreased by FO feeding. In nephritic animals, hepatic cholesterol synthesis was decreased by the 8% casein diets compared with the 20% casein diets, and tended to be reduced by FO feeding between groups at the same casein levels. No effect of diet was observed on fatty acid synthesis among the nephritic rats. FO administration to the nephritic animals suppressed fecal steroid excretion. While lipoprotein lipase activity was unchanged among the nephritic rats, hepatic triglyceride lipase activity was reduced by either the 8% casein or FO diet. The results suggest that the hypolipidemic action of low casein diets may, at least in part, be due to reduced hepatic cholesterol synthesis and suppressed triglyceride secretion from the liver. They also suggest that the hypolipidemic action of FO may, at least in part, be due to reduced hepatic cholesterol synthesis and decreased fatty acid mobilization from peripheral adipose tissue.     

果胶杂质对苎麻纤维及其复合材料性能的影响

研究了苎麻纤维中的果胶杂质对苎麻纤维及其复合材料性能的影响，根据苎麻复合材料综合性能，确定了最佳果胶杂质含量为6．6％。     

The effect of alfalfa-corn diets on cholesterol metabolism and gallstones in prairie dogs

Cholesterol gallstones were present in prairie dogs fed alfalfa plus corn with and without exogenous cholesterol (0.4%). The diets fed to the animals for eight weeks contained alfalfa plus corn in fixed proportions of 50∶50, 85∶15 and 15∶85 (w/w). At sacrifice, all animals were healthy but had not gained weight; no deaths occurred during the experiment. Cholesterol gallstones were present in all groups. In the absence of exogenous cholesterol, the highest stone incidence was found in the animals which received the lowest fiber (highest corn) diets (alfalfa plus corn, 50∶50, 67%; alfalfa plus corn, 15∶85, 83%). Cholesterol gallstone incidence was 100% when exogenous cholesterol was added to the alfalfa plus corn diets (50∶50 and 15∶85). No pigment gallstones were detected in any animal. Liver and plasma cholesterol concentrations were highest in the animals receiving alfalfa plus corn (15∶85) plus 0.4% cholesterol (4.29 mg/g, and 356 mg/dl, respectively). These values were lowest in animals receiving 85% alfalfa plus 15% corn without cholesterol (2.19 mg/g and 88 mg/dl, respectively). Lithogenic indices were below 1.00 in all groups. Biliary bile acids were mainly amidates of cholic acid and chenodeoxycholic acid, with the former predominating. Thus, gallstones can be formed in prairie dogs in the absence of exogenous cholesterol; gallstone incidence is reduced by dietary fiber.     

Studies of serum lecithin-cholesterol acyl transferase activity in rat: Effect of vitamin E deficiency,oxidized dietary fat,or intravenous administration of ozondies or hydroperoxides

Serum lecithin-cholesterol acyl transferase activity in the rat was studied in animals raised on diets devoid of vitamin E or containing oxidized fat and in the serum of normal animals after intravenous administration of hydroperoxides or ozonides. Lecithin-cholesterol acyl transferase activity was suppressed by a vitamin E deficiency but was elevated in the serum of the animals fed diets containing oxidized fat. The intravenous injection of hydroperoxides or ozonides of linoleate into the tail vein of rats caused an immediate depression of serum lecithin-cholesterol acyl transferase activity. The effect of hydroperoxides was more severe than the ozonides, but, with sublethal doses of these compounds, the activity of the enzyme became normal within 24 hr. Hydroperoxides and ozonides also suppressed the activity of lecithin-cholesterol transferase of rat serum of normal animals in vitro. The suppression of lecithin-cholesterol acyl transferase activity by hydroperoxides of ozonides was only partially restored by the addition to the serum of 2-mercaptoethanol.     

Contrasting effects of water-soluble and water-insoluble dietary fibers on bile acid conjugation and taurine metabolism in the rat

The effect of the type of dietary fiber on the bile acid and taurine metabolism was examined in rats. Diets containing 10% of various water-soluble fibers (citrus pectin, konjak mannan, guar gum) as compared to a fiber-free diet increased biliary excretion of total bile acids. In contrast, water-insoluble dietary fibers (cellulose, corn bran, chitin; 10% in the diets) as well as cholestyramine (5% in the diet) considerably, decreased bile acid excretion. Water-soluble dietary fibermediated increases in bile acid excretion were totally attributable to increases in glycine-conjugates. Thus, these fibers greatly increased by the bile acid glycine-to-taurine ratio (G/T). Excretio of glycine conjugates decreased more than that of taurine conjugates in rats fed various water-insoluble dietary fibers. As a results, G/T in rats fed water-insoluble fibers was significantly lowered as compared to G/T in animals fed a fiber-free diet. Cholestyramine did not affect the G/T ratio of bile acids. Fecal bile acid excretion and the activities of hepatic cholesterol 7α-hydroxylase (EC 1.14.13.17) in rats fed various water-soluble dietary fibers approximately doubled as compared to the respective values for rats fed a fiber-free diet. Whereas cholestyramine greatly increased these parameters, water-insoluble fibers did not significantly affect them. Various water-soluble fibers decreased hepatic concentration and urinary excretion of taurine as well as the activity of hepatic cysteine dioxygenase (EC 1.13.11.20). In contrast, water-insoluble fibers considerably increased hepatic taurine concentrations and enzyme activities. The parameters for taurine metabolism were unaffected by cholestyramine. It was suggested that the types of dietary fiber affected hepatic taurine synthesis and thus modified bile acid glycine/taurine ratios.     

棉布支架固定化米根霉联产果胶酶及用于处理烟梗

利用果胶酶处理烟梗纤维生产乳酸等对环境友好,而应用新的发酵组合方式和优化发酵条件是提高产酶量,降低成本的有效途径。本文采用实验室研发的棉布支架固定化米根霉细胞的技术,优化了底物为果胶或烟梗的发酵产果胶酶的培养条件,还优化了处理烟梗果胶的条件。底物为果胶的最佳产酶条件为:转速190r/min,装液量50mL/250mL,发酵温度30℃,初始pH值5,初始孢子浓度0.75×10⁶个/mL。底物为烟梗的最佳产酶条件为:初始pH值4.6、初始孢子浓度0.5×10⁶个/mL等。在优化处理烟梗果胶的条件下,固定化米根霉产果胶酶连续法比游离的果胶酶法降解烟梗果胶的效果好,果胶降解率提高18.5%,达到74.1%。棉布支架固定化米根霉利用果胶发酵产果胶酶量较高,利用烟梗发酵脱胶效果较好。     

Growth, development and dental caries in rats fed two experimental diets

In order to determine the nutritional adequacy of diets MIT 200 and NIH 2000 on the growth and development of experimental animals, these two diets were fed to two groups of animals during three periods of development: 1) pregnancy; 2) lactation, and 3) post-weaning. These diets were compared with a diet that satisfied the requirements of the National Research Council for growth and maintenance. It was found that for the two experimental diets, growth was compromised due to a caloric deficit in both diets. In addition, NIH 2000 was deficient in other nutrients such as iron. Analysis of other parameters such as hemoglobin, hematocrit, salivary protein, saliva flow and weight of vital organs upon autopsy revealed a picture of iron deficiency in the NIH 2000 group. Caries formation can be precipitated by a mechanism influenced by a nutrient deficit.     

Diet,cholesterol metabolism,and atherosclerosis

Effects of diet on acetate incorporation into cholesterol and fatty acids in liver slices, and on the level of plasma cholesterol, were studied in rats and rabbits. Feeding fats and oils in a com-mercial diet stimulated acetate incorporation into rat-liver cholesterol much more than feeding them in a semisynthetic diet. This effect seemed to be specific for cholesterol since incorporation into fatty acids was not similarly affected. High levels of dietary casein inhibited acetate incorporation into both cholesterol and fatty acids. Rat-liver slices generally incorporated more acetate into cholesterol than rabbit-liver slices, but incorpora-tion into fatty acids was often higher in the latter. Rabbit plasma cholesterols were higher on butter diets than on corn oil diets. Further eleva-tion of plasma cholesterol was observed when casein was added to the butter diet but not when it was added to the corn oil diet. Plasma cho-lesterols were elevated, and acetate incorporation into liver cholesterol and fatty acids was inhibited in suckling rats and rabbits whereas recently weaned animals gave results similar to those of adults. The inverse relationship between plasma cholesterol level and acetate incorporation into cholesterol may be attributable to feedback con-trol of liver cholesterol biosynthesis. Other mechanisms which may account for the observed effects of dietary fats and protein on cholesterol metabolism, and the possible relevance of the findings to atherosclerosis, are discussed.     

Cholesterol binding capacity of fiber from tropical fruits and vegetables

The cholesterol binding capacity of 28 fiber samples from a variety of the more common tropical fruits and vegetables was determined. The binding capacity of cholestyramine, cellulose, lignin, guar gum and citrus pectin were also determined. Capacities were evaluated by an in vitro method that simulates the effect of the human digestive system on fiber using a series of enzymatic treatments before the binding was determined. Binding values varied from 3% for a soluble fraction of cassava to 84% for cholestyramine. Values for most fruit and vegetable fiber samples were less than or ca. equal to cellulose or lignin (20% and 16%, respectively). Apart from cholestyramine, sweet potato was the most effective binder (30%). Citrus pectin, at 8%, was a relatively poor binder. The capacity of guar gum (17%) was slightly less than cellulose. These data do not support the conclusion from in vivo studies that the hypocholesteremic effects observed for citrus pectin and guar gum are the result of the direct binding of cholesterol or bile acids in the large intestine. Southern Region, U.S. Department of Agriculture, Agricultural Research Service. Mention of a Trademark or proprietary product is for identification only and does not imply a guarantee or warranty of the product by the U.S. Department of Agriculture over other products that may also be suitable.     

A Fiber-Rich Diet and Radiation-Induced Injury in the Murine Intestinal Mucosa

Dietary fiber is considered a strong intestinal protector, but we do not know whether dietary fiber protects against the long-lasting mucosal damage caused by ionizing radiation. To evaluate whether a fiber-rich diet can ameliorate the long-lasting pathophysiological hallmarks of the irradiated mucosa, C57BL/6J mice on a fiber-rich bioprocessed oat bran diet or a fiber-free diet received 32 Gray in four fractions to the distal colorectum using a linear accelerator and continued on the diets for one, six or 18 weeks. We quantified degenerating crypts, crypt fission, cell proliferation, crypt survival, macrophage density and bacterial infiltration. Crypt loss through crypt degeneration only occurred in the irradiated mice. Initially, it was most frequent in the fiber-deprived group but declined to levels similar to the fiber-consuming group by 18 weeks. The fiber-consuming group had a fast response to irradiation, with crypt fission for growth or healing peaking already at one week post-irradiation, while crypt fission in the fiber-deprived group peaked at six weeks. A fiber-rich diet allowed for a more intense crypt cell proliferation, but the recovery of crypts was eventually lost by 18 weeks. Bacterial infiltration was a late phenomenon, evident in the fiber-deprived animals and intensified manyfold after irradiation. Bacterial infiltration also coincided with a specific pro-inflammatory serum cytokine profile. In contrast, mice on a fiber-rich diet were completely protected from irradiation-induced bacterial infiltration and exhibited a similar serum cytokine profile as sham-irradiated mice on a fiber-rich diet. Our findings provide ample evidence that dietary fiber consumption modifies the onset, timing and intensity of radiation-induced pathophysiological processes in the intestinal mucosa. However, we need more knowledge, not least from clinical studies, before this finding can be introduced to a new and refined clinical practice.     

RFL coated aramid short fiber reinforced thermoplastic elastomer: Mechanical, rheological and morphological characteristics

Composite based on a new generation metallocene catalyzed thermoplastic elastomer ethylene-octene copolymer (EOC) and resorcinol formaldehyde latex (RFL) coated aramid short fiber was prepared by varying the short fiber loading from 1 to 10 phr. The mechanical, morphological and rheological characterizations were carried out. The impact of a low molecular weight maleic anhydride grafted 1, 2 polybutadiene (MA-g-PB) on various properties was also investigated. It has been observed that with increasing the short fiber content both the low strain modulus and modulus at 100% increase but the tensile strength and elongation at break decrease. The improvements in tensile strength coupled with elongation at break and good fiber dispersion particularly at high fiber loaded composite were achieved with the incorporation of MA-g-PB, which indicates that it acts as an interface modifier through compatibilization between the fiber and the EOC matrix as well as a good dispersing agent. The understanding of adhesion between the fiber and the polymer and the sticking of polymer traces on the tensile fractured fiber surface of the composite by scanning electron microscopic analyses further support the compatibilizing action of MA-g-PB. The melt rheological behavior such as storage modulus, loss modulus, complex viscosity and storage viscosity of the composites were investigated using a Rubber Process Analyser (RPA) under strain and frequency sweep mode.     

Nutritional Requirements and Diet Choices of the Pygmy Rabbit (Brachylagus idahoensis): A Sagebrush Specialist

Sagebrush (Artemisia tridentata) comprises up to 99% of the winter and 50% of the summer diets of pygmy rabbits (Brachylagus idahoensis). Few animals specialize on such plants as sagebrush, which contain high levels of plant chemicals that can be toxic. We investigated the nutritional requirements of pygmy rabbits and their ability and propensity to consume sagebrush alone and as part of a mixed diet. We compared diet choices of pygmy rabbits with that of a generalist forager, the eastern cottontail (Sylvilagus floridanus). Pygmy rabbits had a moderately low nitrogen requirement (306.5 mg N/kg^0.75/d), but a relatively high energy requirement, needing 750.8 kJ digestible energy/kg^0.75/d to maintain their body mass while residing in small cages. They digested fiber in pelleted diets similarly to other small hindgut fermenters, but both cottontails and pygmy rabbits digested the fiber in sagebrush better than expected based on its indigestible acid detergent lignin content. Pygmy rabbits consumed more sagebrush than cottontails, regardless of the amount and nutritional quality of supplemental pellets provided. When consuming sagebrush alone, they ate barely enough to meet their energy requirements, whereas cottontails ate only enough sagebrush to meet 67% of theirs. Both rabbit species ate more sagebrush as the quality and quantity of supplemental pellets declined, and more greenhouse-grown sagebrush than sagebrush grown outside. Urine was more acidic when consuming sagebrush than when consuming pellets, indicating detoxification by the liver. Pygmy rabbits do not require sagebrush to survive, but seem to tolerate terpenes and other plant chemicals in sagebrush better than cottontails do.