The Role of Viscosity and Fermentability of Dietary Fibers on Satiety- and Adiposity-Related Hormones in Rats

Dietary fiber may contribute to satiety. This study examined the effect of two dietary fiber characteristics, small intestinal contents viscosity and large intestinal fermentability, on satiety-and adiposity-related hormones in rats. Diets contained fiber sources that were non-viscous, somewhat viscous, or highly viscous, and either highly fermentable or non-fermentable, in a 2 × 3 factorial design. In the fed state (2 h postprandial), rats fed non-fermentable fibers had significantly greater plasma GLP-1 concentration than fermentable fibers. In the fasted state, among non-fermentable fibers, viscosity had no effect on GLP-1 concentration. However, among fermentable fibers, greater viscosity reduced GLP-1 concentration. Plasma peptide tyrosine tyrosine (PYY) concentrations in the fasted state were not influenced by the fermentability of the fiber overall, however animals consuming a fructooligosaccharide greater PYY concentration. In both the fed and fasted states, rats fed non-fermentable fibers had a significantly lower plasma ghrelin concentration than rats fed fermentable fibers. In the fasted state, rats fed non-fermentable fibers had a significantly lower plasma leptin concentration than rats fed fermentable fibers. Thus, fermentability and viscosity of dietary fiber interacted in complex ways to influence satiety- and adiposity-related plasma hormone concentrations. However, the results suggest that highly viscous, non-fermentable fibers may limit weight gain and reduce adiposity and non-fermentable fibers, regardless of viscosity, may promote meal termination.     

Fermentative characteristics of cereal brans and vegetable fibers

Dietary fiber has been suggested to alter the colonic environment and protect against colorectal diseases, but several recent epidemiological studies indicate that cereal and vegetable fibers may not confer the same benefit. To address this issue, five common cereal brans (barley, corn, oat, rice, and wheat) and five vegetable fiber isolates (broccoli, cabbage, carrot, cauliflower, and lettuce) were fermented in vitro with human fecal microbiota for 4, 8, 12, and 24 hours. Short‐chain fatty acid (SCFA), hydrogen (H2), and methane (CH4) productions and neutral‐detergent fiber (NDF) digestibility differed significantly with fiber source. The vegetable fibers were significantly more fermentable than were the cereal brans, as evidenced by greater NDF digestibility and increased productions of SCFA, H2, and CH4, despite the presence of fermentable starch and protein in the latter. We concluded that vegetable fibers may more effectively stimulate colonic fermentation than cereal brans do. These findings suggest an attribute (i. e., fermentability) that may partially explain previously observed differences between vegetable and cereal fiber consumption patterns and colorectal carcinogenesis.     

Fermentative characteristics of cereal brans and vegetable fibers

Dietary fiber has been suggested to alter the colonic environment and protect against colorectal diseases, but several recent epidemiological studies indicate that cereal and vegetable fibers may not confer the same benefit. To address this issue, five common cereal brans (barley, corn, oat, rice, and wheat) and five vegetable fiber isolates (broccoli, cabbage, carrot, cauliflower, and lettuce) were fermented in vitro with human fecal microbiota for 4, 8, 12, and 24 hours. Short-chain fatty acid (SCFA), hydrogen (H2), and methane (CH4) productions and neutral-detergent fiber (NDF) digestibility differed significantly with fiber source. The vegetable fibers were significantly more fermentable than were the cereal brans, as evidenced by greater NDF digestibility and increased productions of SCFA, H2, and CH4, despite the presence of fermentable starch and protein in the latter. We concluded that vegetable fibers may more effectively stimulate colonic fermentation than cereal brans do. These findings suggest an attribute (i.e., fermentability) that may partially explain previously observed differences between vegetable and cereal fiber consumption patterns and colorectal carcinogenesis.     

Dilution effect of dietary fiber sources: An in vivo study in the rat

The in vivo diluting ability of dietary fiber was tested by providing 90 male Sprague-Dawley rats with a fiber-free control diet, or that diet diluted by 8% dietary fiber from pectin, guar, cellulose, wheat bran or oat bran. Chromic oxide, a nonabsorbable marker, was incorporated into all diets at 0.4% by weight. In vivo samples of colonic contents from the cecum, proximal and distal colon were analyzed for chromium concentration using atomic absorption spectrophotometry. Twenty-four-hour fecal collections determined which fibers contributed most to fecal weight. The less fermentable fibers (cellulose and wheat bran) produced the heaviest 24 h fecal collections (P<0.05) and the best in vivo dilution effect (P<0.01). The more fermentable fibers (pectin, guar, and oat bran) dit not increase 24 h fecal weight, but did provide a moderate in vivo dilution effect when compared to controls (P<0.05).     

Effect of fiber from fruits and vegetables on metabolic responses of human subjects I. Bowel transit time, number of defecations, fecal weight, urinary excretions of energy and nitrogen and apparent digestibilities of energy, nitrogen, and fat

Twelve men 37 to 58 years of age consumed two diets for a period of 26 days each in a cross-over design. The high fiber diet contained fruits and vegetables and the lower fiber diet contained fruit and vegetable juices. Neither diet contained whole grain cereals or nuts. Some nutrients were added to the low fiber diet in order to make the diets equivalent insofar as possible in all respects except fiber. The inclusion of fruits and vegetables in the diet decreased bowel transit time, increased fecal weight, increased number of defecations, increased fecal excretions and decreased apparent digestibilities of energy, nitrogen, and fat. Six of the 12 subjects had diastolic blood pressure of 80 or more when consuming the low fiber diet. The diastolic blood pressures of these six men were significantly lower when the high fiber diet was consumed.     

Fiber, stool bulk, and bile acid output: implications for colon cancer risk

Dietary fiber has direct effects on stool bulk and bile acid output that may be of relevance in the etiology of colon cancer. Most types of fiber increase the total volume of stool and reduce the concentration of specific substances, including bile acids, that are in contact with the bowel wall. However, fibers differ in their effect on stool bulk, with wheat fiber being a more effective stool bulking agent than fruit and vegetable fibers. In addition, the extent to which a specific fiber reduces bile acid concentration will be modified by its concomitant effects on total fecal sterol excretion. Whereas wheat bran reduces fecal bile acid concentration, pectin, lignin, and oat bran do not. These three fibers significantly increase total bile acid output. Bile acids act as promoters of colonic tumors in mutagenesis assay systems and in various animal models. Human epidemiological studies show a relationship between various dietary variables, including fat and fiber intake, fecal concentration of bile acids, and colon cancer risk.     

Methane production and bowel function parameters in healthy subjects on low- and high-fiber diets.

Colon cancer patients are more likely than healthy subjects to excrete breath methane, and methane production has been suggested as a screening method to predict risk of developing colon cancer. To assess whether methane production is related to fiber ingestion and bowel function, we measured end-alveolar breath methane in 126 healthy subjects; 36% produced methane (greater than 3 ppm). Fifteen methane producers and nine controls were selected to participate in a 17-day study: a self-selected diet for 7 days, followed by the same diet plus 24 g/day dietary fiber (Fiber One Cereal) for 10 days. Methane was measured three times per day on three days during each diet. Two subjects screened as methane producers stopped excreting methane during the study, and one control started to excrete methane. Radiopaque pellets were given at the start and end of each diet, and feces were collected, homogenized, and dried. Mean transit time (p less than 0.0001) and fecal pH (p less than 0.0003) were significantly decreased with fiber, whereas fecal hydration scale (p less than 0.003), fecal dry (p less than 0.0001) and wet (p less than 0.0001) weight, and frequency of defecation (p less than 0.0006) were significantly increased with fiber. No significant change in methane excretion (p less than 0.057) was seen with added fiber. Thus, in this study methane excretor status was not constant in healthy subjects and was not significantly changed by 24 g/day dietary fiber as Fiber One Cereal.     

Major Cereal Grain Fibers and Psyllium in Relation to Cardiovascular Health

Numerous studies reveal the cardiovascular benefits of consuming dietary fiber and, especially, cereal fiber. Cereal fiber is associated with cardiovascular risk reduction through multiple mechanisms and consuming a variety of cereal fiber sources offers health benefits specific to the source. Certain cereal fibers have been studied more extensively than others and provide greater support for their incorporation into a healthful diet. β-glucan from oats or barley, or a combination of whole oats and barley, and soluble fiber from psyllium reduces the risk of coronary heart disease; inulin-type fructans added to foods and beverages may modestly decrease serum triacylglycerols; arabinoxylan and resistant starch may improve glycemic control. Individuals with low cereal fiber intake should increase their intake of whole grains in order to receive the benefits of whole grains in addition to fiber. For those adjusting to the texture and palatability of whole grains, turning to added-fiber products rich in β-glucan and psyllium may allow them to reach their fiber goals without increasing caloric intake.     

Effects of coingestion of different fibers on fecal excretion and cecal fermentation in rats

The effects of the concurrent ingestion of 2 dietary fibers of different fermentabilities on fecal excretion and cecal fermentation were examined in rats. Poorly fermentable, low-molecular-weight sodium alginate supplementation of a fiber-free diet increased fecal excretion and the water content dose-dependently but did not affect cecal pH. Highly fermentable guar gum hydrolysate supplementation decreased cecal pH dose-dependently, whereas there was only a slight increase in fecal excretion. The concurrent ingestion of both fibers increased fecal excretion, lowered cecal pH, and increased the fecal water content and cecal short-chain fatty acids, especially butyrate. The increases in both fecal excretion and cecal fermentation were not achieved by excessive ingestion of the respective fibers alone and were also observed in loperamide-induced constipation. In conclusion, the concurrent ingestion of low-molecular-weight sodium alginate and guar gum hydrolysate increases both fecal excretion and cecal fermentation as a consequence of each fiber compensating for their respective dietary disadvantages in a complementary manner.     

Gastrointestinal effects of modified guar gum and soy polysaccharide as part of an enteral formula diet.

Dietary fiber supplementation may improve gastrointestinal tolerance and decrease diarrhea in patients receiving enteral formula diets. To compare the effects of two dietary fibers on bowel function parameters and short-chain fatty acid excretion we fed 11 healthy men three defined enteral formula diets in random order for 18 days each. The test diets consisted of a fiber-free formula and daily intakes of maltodextrin (0 g of fiber), 15 g of total dietary fiber as an enzymatically modified guar gum, and 15 g of total dietary fiber as soy polysaccharide. Data were also collected while subjects consumed self-selected diets for 5 days. Mean transit time was longer and fecal moisture content was lower on 0 g of fiber and modified guar than on the self-selected and soy diets. Furthermore, mean transit time was slightly longer and fecal nitrogen excretion greater on modified guar compared with 0 g of fiber. Daily fecal output and frequency of defecation were greater, fecal pH was lower, and fecal butyrate concentrations were higher on the self-selected diet compared with the enteral formula diets. However, there was no difference in these parameters among the three liquid diets. Thus, despite significant differences in mean transit time, few differences in other parameters of bowel function were observed when healthy subjects consumed enteral formula diets containing 0 g of fiber and 15 g of total dietary fiber as modified guar and soy.     

Rye bread improves bowel function and decreases the concentrations of some compounds that are putative colon cancer risk markers in middle-aged women and men

Cereal fiber may reduce the risk of colorectal cancer by diluting colonic contents due to increased fecal output, by accelerating intestinal transit, by increasing fecal frequency and by altering bacterial metabolism. The effects of whole-meal rye bread on some putative colon cancer risk markers were investigated in 17 healthy Finnish subjects using a randomized crossover trial with two 4-wk bread consumption periods and a 4-wk washout period between the bread periods. White wheat bread was used as a control. Test breads covered a minimum of 20% of the daily energy intake (range, 4330-14, 033 kJ/d). Intestinal transit time, stool weight, fecal bacterial enzyme activities and short-chain fatty acid, ammonia, diacylglycerol (DAG) and bile acid concentrations in feces (expressed per gram wet feces) were measured. Whole-meal rye bread significantly increased fecal output and fecal frequency and shortened mean intestinal transit time compared with wheat bread in both women and men. Activities of beta-glucuronidase and beta-glucosidase (expressed per gram wet feces) were significantly lower in men and urease activity significantly higher in women during the rye bread period (RBP). Fecal butyrate concentration was higher during the RBP in men. Fecal ammonia and DAG concentrations did not differ between bread periods. Fecal total and secondary bile acid concentrations were significantly lower during RBP in both women and men. This study shows that whole-meal rye bread significantly improves bowel function in healthy adults and may decrease the concentration of some compounds that are putative colon cancer risk markers.     

Fermentable dietary fibers elevate urinary methylmalonate and decrease propionate oxidation in rats deprived of vitamin B-12

This study examines the effect of dietary fiber supplements of different degrees of bacterial fermentability on biochemical indicators of vitamin B-12 deficiency in rats. Groups of rats were fed a fiber-free diet deficient in vitamin B-12 or the fiber-free diet diluted with 5% of a poorly fermentable dietary fiber (cellulose, lignin or alginic acid) or a highly fermentable fiber (pectin, guar gum or xylan). Poorly fermentable fibers had no significant effect on apparent B-12 status, whereas the highly fermentable fibers significantly increased urinary methylmalonic acid and depressed oxidation of [14C]propionate to 14CO2. Pectin consistently induced significantly greater effects than did xylan or guar gum. The data are consistent with the hypothesis that fermentable fibers stimulate bacterial propionate production and exaggerate certain biochemical indicators of B-12 deficiency. Since pectin had a more pronounced effect than did other fermentable fibers, the possibility that pectin may also interfere with B-12 absorption requires further study.     

Identifying Practical Solutions to Meet America’s Fiber Needs: Proceedings from the Food & Fiber Summit

Fiber continues to be singled out as a nutrient of public health concern. Adequate intakes of fiber are associated with reduced risk for cardiovascular disease, cancer, diabetes, certain gastrointestinal disorders and obesity. Despite ongoing efforts to promote adequate fiber through increased vegetable, fruit and whole-grain intakes, average fiber consumption has remained flat at approximately half of the recommended daily amounts. Research indicates that consumers report increasingly attempting to add fiber-containing foods, but there is confusion around fiber in whole grains. The persistent and alarmingly low intakes of fiber prompted the “Food & Fiber Summit,” which assembled nutrition researchers, educators and communicators to explore fiber’s role in public health, current fiber consumption trends and consumer awareness data with the objective of generating opportunities and solutions to help close the fiber gap. The summit outcomes highlight the need to address consumer confusion and improve the understanding of sources of fiber, to recognize the benefits of various types of fibers and to influence future dietary guidance to provide prominence and clarity around meeting daily fiber recommendations through a variety of foods and fiber types. Potential opportunities to increase fiber intake were identified, with emphasis on meal occasions and food categories that offer practical solutions for closing the fiber gap.     

High-Fiber Diet during Pregnancy Characterized by More Fruit and Vegetable Consumption

Higher dietary fiber intakes during pregnancy may have the potential health benefits of increasing gut microbiome diversity, lowering the risk of glucose intolerance and pre-eclampsia, achieving appropriate gestational weight gain, and preventing constipation. In this observational cohort study, we have assessed the dietary fiber intakes of 804 women in late pregnancy, using a semi-quantitative food frequency questionnaire (SQ-FFQ). Overall, the median (interquartile range) dietary fiber intake was 24.1 (19.0–29.7) grams per day (g/day). Only 237/804 (29.5%) women met the recommended Adequate Intake (AI) of dietary fiber during pregnancy of 28 g/day. Women consuming the highest quartile of fiber intakes (34.8 (IQR 32.1–39.5) g/day) consumed more fruit, especially apples and bananas, than women consuming the lowest quartile of fiber intakes (15.9 (IQR 14.4–17.5) g/day). These women in the highest fiber-intake quartile were older (p < 0.01), more had completed further education after secondary school (p = 0.04), and they also consumed more vegetables (67 g/day) compared to the women in the lowest fiber consumption quartile (17 g vegetables/day). Bread intakes of 39–42 g/day were consistent in quantities consumed across all four fiber-intake quartiles. Our findings suggest that antenatal education advice targeting increased fruit and vegetable consumption before and during pregnancy may be a simple strategy to achieve increased total dietary fiber intakes to reach recommended quantities.     

Healthy Subjects Experience Bowel Changes on Enteral Diets

Background: Tube‐fed patients frequently suffer from abnormal bowel function that affects intestinal bacteria and quality of life. Dietary fiber affects laxation and can be fermented by gut bacteria to metabolites that influence gut health and fecal moisture. The aim of this study was to compare the effects of a fiber‐blend fortified enteral formula (FB, 15 g/L), a fiber‐free formula (FF), and habitual diet on bowel function, fecal bacteria, and quality of life. Materials and Methods: In a randomized, double‐blind, crossover design, 20 healthy subjects consumed both FF and FB for 14 days with a 4‐week washout. A 5‐day fecal collection was used to assess stool output, whole‐gut transit time (WGTT), total bacteria, bifidobacteria, lactobacilli, clostridia, and bacteroides. Subject gastrointestinal quality of life index (GIQLI) and side effects were also measured. Results: On formula diets, 5‐day fecal output decreased by >55% from habitual diet, but was 38% higher on FB than FF (P = .0321). WGTT was approximately 1.5 times longer on formula diets than habitual diet (P < .0004). Total bacteria declined from habitual diet on FF (P < .004), but not on FB. Numbers of bifidobacteria and lactobacilli declined from habitual diet on both formula diets, but bifidobacteria was higher on FB compared with FF (P < .0001). Bacteroides and clostridia numbers did not change between diets. GIQLI and incidence of gas symptoms did not differ between formulas. Conclusions: Addition of a fiber blend moderated changes in bowel function and gut bacteria observed in healthy subjects consuming FF. These results support adding mixed fiber sources to enteral nutrition if no contraindication exists.     

Guar gum and similar soluble fibers in the regulation of cholesterol metabolism: Current understandings and future research priorities

The hypocholesterolemic effects associated with soluble fiber consumption are clear from animal model and human clinical investigations. Moreover, the modulation of whole-body cholesterol metabolism in response to dietary fiber consumption, including intestinal cholesterol absorption and fecal sterol and bile acid loss, has been the subject of many published reports. However, our understanding of how dietary fibers regulate molecular events at the gene/protein level and alter cellular cholesterol metabolism is limited. The modern emphasis on molecular nutrition and rapid progress in ‘high-dimensional’ biological techniques will permit further explorations of the role of genetic polymorphisms in determining the variable interindividual responses to soluble fibers. Furthermore, with traditional molecular biology tools and the application of ‘omic’ technology, specific insight into how fibers modulate the expression of genes and proteins that regulate intestinal cholesterol absorption and alter hepatic sterol balance will be gained. Detailed knowledge of the molecular mechanisms by which soluble fibers reduce plasma cholesterol concentrations is paramount to developing novel fiber-based “cocktails” that target specific metabolic pathways to gain maximal cholesterol reductions.     

复合膳食纤维对大鼠降脂效果观察

目的：制备复合膳食纤维（dietary fiber,DF），并探讨其与3种单一 的DF对高脂血症大鼠体内脂类含量的影响。方法：健康、雌性、断乳Wistar大鼠48只，按体重随机分为6组，用高脂饲料诱发高酯血症的同时，分别添加10％的DF：纤维素（B组）、果胶（C组）、海藻酸钠（D组）、纤维素－果胶复合物（E组）、纤维素－海藻酸钠复合物（F组），以单纯的高脂饲料组为对照组（A组），8周后观察各种DF对大鼠的生长发育及脂类代谢的影响。结果：（1）添加10％的各种DF不影响大鼠的生长发育。（2）与对照组比，各种DF中不同程度降低大鼠脂质水平，且以复合物效果为佳。（3）各种DF可不同程度地增加粪重和粪酯排出量（P＜0．05，D组除外），以复合物为明显。（4）相关分析显示，血清TC、TG、LDL－C含量与粪脂含量呈负相关（P＜0．01）。结论：各种DF皆可不同程度地降低大鼠体内脂类含量，春中可溶性DF效果优于不可溶性DF，而复合DF的效果又优于单一的DF。     

Relationship between Dietary Fiber Intake and the Prognosis of Amytrophic Lateral Sclerosis in Korea

The gut microbiota has been suggested as an important factor in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS). This study aimed to investigate whether the intake of different kinds of dietary fiber was related to the disease progression rate (∆FS) and survival time. In total, 272 Korean sporadic ALS patients diagnosed according to the revised EI Escorial criteria were recruited starting in March 2011 and were followed until the occurrence of events or the end of September 2020. The events included percutaneous endoscopic gastrostomy, tracheostomy, and death. Dietary fiber intake was calculated based on a 24-h dietary recall and classified according to five major fiber-rich foods: vegetables, fruits, grains, legumes, and nuts/seeds. Among the total participants, the group with ∆FS values lower than the mean ∆FS (0.75) was noted in the highest tertiles of total and vegetable fiber intake. Participants in the highest tertile for vegetable fiber intake showed longer survival in the Kaplan–Meier analysis (p = 0.033). Notably, vegetable fiber intake was negatively correlated with pro-inflammatory cytokine (interleukin (IL)-1β, IL-6, and monocyte chemoattractant protein-1) levels in the cerebrospinal fluid. This study showed that vegetable fiber intake could influence the disease progression rate and survival time. Further clinical trials are needed to confirm whether dietary fiber supplementation improves the prognosis of ALS.     

Cholesterol-lowering effects and utilization of protein, lipid, fiber and energy in rats fed unprocessed and baked oat bran.

The effects of the addition of 15% or 30% non-heated oat bran or 30% baked oat bran to a purified diet on apparent digestibility of dry matter, protein, lipid and fiber were measured in balance experiments with male Wistar rats. The effects of oat bran on dietary metabolizable energy, fecal bulking capacity and transit time of the ingested food were also studied. Heat processing of oat bran occurred in conditions of moisture and temperature similar to those of bread baking. Compared with the unprocessed oat bran, the baked product had a higher content of insoluble fiber, mainly due to higher Klason lignin content and a shift from soluble to insoluble beta-glucans. Relative to the fiber-free control diet, feeding the oat bran diets increased wet and dry fecal weight and decreased the transit time of the food. Fecal bulking capacity increased proportionally with oat fiber intake. Metabolizable energy of the diets, as well as apparent digestibility of dry matter and protein decreased with oat bran supplementation; on the other hand, lipid digestibility was not significantly changed. Baking of oat brain resulted in no statistically significant effects on dietary metabolizable energy or apparent digestibility of dry matter, protein, lipid and fiber. The measured metabolizable energy of oat bran ranged between 12.7 and 13.2 MJ/kg. Total plasma cholesterol concentration diminished with oat brain intake; non-heated and baked oat bran had comparable effects on plasma cholesterol. An inverse linear relationship (r = -0.80, P less than 0.1) was found between plasma cholesterol concentration and fecal excretion of bile acids.     

Effects of rice fiber on fecal weight, apparent digestibility of energy, nitrogen and fat, and degradation of neutral detergent fiber in young men

The effects of rice fiber on fecal weight, transit time, frequency of defecations, digestibility of nutrients and blood status were investigated in 5 healthy young men. Each of them consumed a brown rice diet and then a polished rice diet for 2 weeks respectively. Both diets contained 1.2 g protein per kg body weight. The brown rice diet contained 2 times as much dietary fiber as the polished rice diet. When they consumed the brown rice diet, it showed an increase of fecal weight and decrease of digestibility of energy, nitrogen and fat. Nitrogen balance was not significantly different and kept zero balance on both diets. Concentration of plasma cholesterol was not significantly different. The results suggest that rice fiber produced an increase in fecal weight, which is assumed to be effective in preventing colonic disease in advanced countries and does not affect plasma lipid level.