Hydrogen and methane production by human subjects consuming various diets with and without dietary fiber

Production of breath hydrogen and methane was related to colonic degradation of fiber to determine whether breath gases were good indicators of colonic fiber breakdown. End-alveolar breath hydrogen and methane were measured in five male subjects consuming three diets: their self-selected diet (SS), a fiber-free diet (FF), and the same fiber free diet plus 75 grams of coarse white wheat bran (B). On each diet, end-alveolar breath samples were collected hourly from 0800 to 2200 hours for hydrogen analysis. Hydrogen production after ingestion of a 15 gram dose of lactulose (L) was also determined. Methane production was determined twice during each diet. Neutral detergent fiber (NDF) of the bran and the fecal composites from the bran diet were measured. Average peak hydrogen production was 64 PPM (range 39–113) during the self-selected (SS) diet and 35 PPM (range 14–59) during the liquid fiber-free diet (FF). Bran ingestion caused hydrogen production to increase to an average peak value of 44 PPM (range 25–74). Lactulose ingestion generally resulted in more hydrogen production, with an average peak of 76 PPM (range 30–142). NDF was calculated to be about 40% digestible (range 27% to 48%) during bran ingestion. These results suggest that less hydrogen is produced on a fiber-free liquid diet than on diets known to contain undigestible carbohydrates. A hydrogen breath test may be used as an indirect measure of fiber digestibility since lactulose, which is highly fermentable, produced a little less than twice the peak hydrogen response than did bran whose digestibility was calculated to be roughly 40%.     

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).     

Effects of corn oil and wheat brans on bile acid metabolism in rats

High concentrations of colonic bile acids may promote tumor formation. Some studies have found that high levels of dietary fat increase fecal bile acid excretion, whereas others report no effect. Wheat bran appears to reduce fecal bile acid concentration. This study was conducted to determine the effect of different dietary fat levels and types of wheat bran on bile acid metabolism. Rats were fed diets containing either no fiber, 2% cholestyramine (CHO) or brans of hard red spring, soft white winter or durum wheat--at both a 5 or 20% fat level. Animals were fed for 7 wk, and feces were collected in the last week. Wheat bran (all types) significantly increased fecal mass approximately fourfold, and CHO significantly increased fecal mass twofold compared to the fiber-free diet. Increasing the fat level did not increase fecal bile acid excretion, nor did the addition of wheat bran. Addition of CHO, however, more than doubled it. CHO increased fecal bile acid concentration, all wheat brans decreased it and fat level had no effect. Bile acid pool size was increased slightly by fat level and cholestyramine feeding but not by wheat brans. These results indicate that fat level slightly alters bile acid metabolism but that wheat brans do not.     

Dietary wheat bran inhibits DNA synthesis and enhances 5-fluorouracil toxicity in rat pancreas

The effect of a 20% wheat bran dietary supplement on pancreatic growth and on the content and synthesis of pancreatic RNA and DNA was examined in male Sprague-Dawley rats fed defined diets for 4-5 weeks. Nutrient intake and body weight gain were similar in the control group (fed a fiber-free diet) and the groups fed the wheat bran supplement. The wheat bran diet produced no significant change in pancreatic weight, protein, RNA content, or DNA content, but was associated with a 28.8% fall in pancreatic DNA synthesis, measured by [3H]thymidine incorporation into DNA, when compared with the controls (p less than 0.05). When rats were injected with 50 mg/kg of 5-fluorouracil (two injections, one week apart), those fed wheat bran exhibited a 40.1% increase in pancreatic wet weight (p less than 0.005) and a 24.5% decrease in RNA content (p less than 0.001), when compared to controls fed a fiber-free diet. RNA synthesis, measured by the incorporation of 32P into RNA, increased 3.6-fold in rats fed wheat bran, when compared with controls (p less than 0.01). These results suggest that wheat bran should be tested further for any inhibitory action on pancreatic carcinogenesis and for its modifying effect on 5-fluorouracil toxicity.     

Bile acid metabolism in rats fed two levels of corn oil and brans of oat, rye and barley and sugar beet fiber.

High concentrations of fecal bile acids are associated with a higher incidence of colon cancer. Dietary changes that alter bile acid metabolism are therefore of interest. Here, we report the effect of feeding diets containing four fiber sources and two fat levels for 7 wk on bile acid excretion and small intestinal bile acids (an index of pool size) in rats. The fiber sources were oat bran, rye bran, barley bran and sugar beet fiber. Fiber-containing diets were 8% dietary fiber and contained either 5 or 20% corn oil. All fiber sources caused significantly greater fecal output compared with the fiber-free basal diet. All fiber sources also resulted in significantly (P less than 0.05) lower fecal bile acid concentration compared with the fiber-free basal diet. Only rye bran resulted in significantly (P less than 0.05) higher total fecal bile acid excretion. Oat bran resulted in a slightly but significantly (P less than 0.05) higher quantity of small intestine bile acids compared with the other diets. Dietary fat level had no significant effect on fecal bile acid concentration or excretion or quantity of small intestinal bile acids. We conclude that all four fiber sources tested resulted in lower fecal bile acid concentration, by effectively causing greater fecal mass. Changes in dietary fat level as corn oil had no effect on fecal bile acids.     

Response to dietary wheat bran in the exocrine pancreas and intestine of rats

Rats were fed a fiber-free (FF) mixture or the same diet with a supplement of 20% wheat bran (WB). After 2 weeks, the pancreas contained higher levels of amylase and trypsin in rats fed WB. In response to a meal, the intestine contained more lipase activity in the WB group. The dry weight of material and protein level in the intestinal contents were also elevated in the WB group. The size of the intestinal villi had not changed, but it did contain more goblet cells. The results indicate that consumption of wheat bran can lead to changes in the exocrine pancreas, perhaps associated with shifts in gut hormones, and may effect absorption by increasing the bulk of material as well as enhancing mucus production in the intestine.     

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.     

Using density rather than mass to express the concentration of gastrointestinal tract constituents

This experiment had two objectives: to develop an analytical technique to measure the density of digesta and fecal samples; to determine whether this measurement is physiologically relevant. To address the latter question, rats were provided with one of five high-fiber diets or a fiber-free control diet, and density determinations were made on samples from the cecum, proximal and distal colon, and from a passed fecal pellet. The density of colonic contents varied with the fiber component of the diet. The fiber-free control diet produced the densest stool at all sites studied (P less than 0.01), whereas wheat bran produced the least dense stool at every site (P less than 0.01). There were also density differences among bowel positions within diet treatments: the stool from those animals consuming the fiber-free, guar and pectin diets became denser as it moved distally; wheat bran, on the other hand, produced the opposite effect--the more distal the stool traveled, the less dense it became. Since the density of colonic contents varied with respect to both diet and anatomical site, these data suggest that the traditional technique of expressing the concentration of a constituent of interest (e.g., bile acid, volatile fatty acid) per gram of digesta or fecal matter may not always be appropriate. This is particularly true if exposure of the intestinal mucosal cells to a substance in the digesta or fecal stream is of interest, since density, rather than mass, reflects the diluting potential of the diet.     

Bioavailability of vitamin B-6 from rat diets containing wheat bran or cellulose

Bioavailability of vitamin B-6 (B-6) in the total diet was studied in male, weanling Sprague-Dawley rats fed fiber-free (FF) diets with 0.2 or 6.9 mg pyridoxine/kg diet (0-, 2- or 6.9-PYR), 20% wheat bran (WB) diets with 3.9- or 5.5-PYR or 7% cellulose (C) diets with 0- or 2-PYR for 28 d. Body weight gain (mean +/- SEM) with 0-PYR was 70 +/- 9.0 and 81.2 +/- 4.2 g for FF and C, respectively. All other groups gained 170-180 g. Urinary excretion of 4-pyridoxic acid (4-PA), a major B-6 metabolite, for FF groups was 1.31 +/- 0.22, 2.26 +/- 0.28 and 6.39 +/- 1.73 micrograms/24 h, at 0-, 2- and 6.9-PYR, respectively. Rats fed WB diets excreted 4.99 +/- 0.58 and 9.81 +/- 0.76 micrograms/24 h (3.9- and 5.5-PYR, respectively) and those fed C diets excreted 1.46 +/- 0.34 and 2.69 +/- 0.72 micrograms/24 h (0- and 2-PYR). There was increasing turnover and shorter biological half-life of [14C]pyridoxine (1 mu Ci injected on d 1) with increasing dietary B-6. Growth, 4-PA and 14C turnover data indicated that WB contributed to B-6 intake of these rats. Cellulose acted as a simple dietary diluent and had no effect on indices of B-6 status. These data suggest that dietary fiber, as cellulose or the indigestible component of wheat bran, does not adversely affect the bioavailability of vitamin B-6.     

The effects of guar gum or wheat bran on the disappearance of 14C-labeled starch from the rat gastrointestinal tract

An animal model was used to test the hypothesis that guar gum, a source of soluble fiber, will slow the disappearance of starch from the gastrointestinal tract. Male Wistar rats were adapted for 1 wk to a purified diet and then divided into three groups and given 30 min to consume a test meal. The test meal contained 5% fiber derived from guar gum (GG) or wheat bran (WB) or was fiber-free (FF), and each contained 2.5 microCi 14C-labeled starch. At 1, 2.5, or 5 h postprandial, a group from each dietary treatment was killed, and stomach, small and large intestine and cecum were removed to determine the distribution of radioactivity. The isotope emptied from the stomach at a similar rate for all three groups. The percent ingested dose in the small intestine (SI) was highest in the upper half at 1 h and highest in the lower half at 2.5 h for all groups. The percent ingested dose of 14C-starch was significantly higher from upper SI segments in the GG group than from those in the FF group at 2.5 and 5 h, whereas percent ingested dose did not differ in the upper SI segments in the WB group compared to the FF group at 1, 2.5 and 5 h. These data indicate that a viscous polysaccharide (GG) can delay the disappearance of starch from the SI whereas a source of insoluble fiber (WB) did not slow starch disappearance.     

Effect of dietary fiber on the disposition and excretion of a food carcinogen (2-14C-labeled MeIQx) in rats.

We studied to what extent dietary fiber may affect uptake, retention, and excretion of a food carcinogen (2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, MeIQx) occurring in fried meat. Four diets--one fiber-free control and three containing either insoluble dietary fiber isolated from sorghum (100 g/kg) and wheat bran (100 g/kg) or the highly soluble pectin (50 g/kg)--were investigated. The fiber diets were given in amounts of 10 g/day to rats. Thus, each rat received 1 or 0.5 g fiber and 100 micrograms 2-14C-labeled MeIQx uniformly mixed in its daily diet. A 4-day adaptation period with unlabeled MeIQx was followed by a 5-day experimental period with 14C-labeled MeIQx, during which urine and feces were collected separately for analysis of radioactivity and mutagenicity. Furthermore the composition and the fermentability of the dietary fiber were determined. The present study shows that a diet containing fiber, especially fiber isolated from sorghum and wheat bran, affects the excretion pattern of the food carcinogen MeIQx in a manner suggesting a lower uptake and a decreased transit time through the gastrointestinal tract in a more diluted form than a nonfiber diet. Furthermore, less radioactivity was retained in the kidneys with sorghum and wheat bran than with the other two diets. On the other hand, none of these types of dietary fiber affected the retention of the hepatocarcinogen MeIQx in the liver 24 hours after the last oral intake. DNA adducts were formed to a higher extent in the kidney than in the liver. The highest levels were found in animals given the wheat bran diet.     

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.     

Effect of wheat bran on bowel function and fecal calcium in older adults

Seven healthy older volunteers participated in a 33-day study consisting of three sample collection periods, a 10-day control, and two 10-day experimental periods. Subjects consumed their usual self-selected diets throughout and a daily wheat bran supplement (30 g) during the two experimental periods. Food intake was recorded daily by subjects and accuracy and completeness checked daily by personal interview. Apparent calcium absorption decreased significantly from 22.1 +/- 5.6% (mean +/- SD) during the control to 8.6 +/- 5.2% during the second bran period. The wheat bran supplement significantly increased wet and dry stool weights but had no effect on stool moisture or defecation frequency. Gastrointestinal transit time of a dose of chromium decreased significantly, from 75 +/- 33 to 54 +/- 19 hr; of a dose of polyethylene glycol insignificantly, from 98 +/- 59 to 69 +/- 46 hr. Mean recovery of 21 doses of chromium of 98.7 +/- 5.0% verified that stool collection was complete. The results suggest that the ability of wheat bran to regulate bowel function in the apparently healthy older adult may be accompanied by increased fecal calcium losses similar to what has been reported for younger adults.     

Serum lipid and fecal bile acid changes with cereal, vegetable, and sugar-beet fiber feeding.

Thirty-four subjects consumed six controlled formula diets for 3 wk each, supplemented with 0 g added fiber, 10 and 30 g dietary fiber as wheat bran (WB), 10 and 30 g dietary fiber as mixed vegetable fiber (VF), and 30 g dietary fiber as sugar-beet fiber (SBF). Serum cholesterol changes for fiber free, 10 g WB, 30 g WB, 10 g VF, 30 g VF, and 30 g SBF (-0.13, -0.18, -0.05, -0.17, -0.24, and -0.70 mmol/L, respectively) were significant for 30 g VF and 30 g SBF. Reduction in total cholesterol with SBF was largely due to significant lowering of low-density-lipoprotein cholesterol. Total fecal bile acid concentrations were significantly higher with the fiber-free diet than with 30 g WB, VF, and SBF (P less than 0.001) and were also higher with 30 g SBF than with 30 g WB and 30 g VF (P less than 0.005). Daily fecal bile acid excretion was not different on 30 g SBF compared with 30 g WB and 30 g VF. Differences in cholesterol reduction across the diets could not be explained by differences in fecal bile acid excretion.     

Program

Seven healthy older volunteers participated in a 33-day study consisting of three sample collection periods, a 10-day control, and two 10-day experimental periods. Subjects consumed their usual self-selected diets throughout and a daily wheat bran supplement (30 g) during the two experimental periods. Food intake was recorded daily by subjects and accuracy and completeness checked daily by personal interview. Apparent calcium absorption decreased significantly from 22.1 +/? 5.6% (mean +/? SD) during the control to 8.6 +/? 5.2% during the second bran period. The wheat bran supplement significantly increased wet and dry stool weights but had no effect on stool moisture or defecation frequency. Gastrointestinal transit time of a dose of chromium decreased significantly, from 75 +/? 33 to 54 +/? 19 hr; of a dose of polyethylene glycol insignificantly, from 98 +/? 59 to 69 +/? 46 hr. Mean recovery of 21 doses of chromium of 98.7 +/? 5.0% verified that stool collection was complete. The results suggest that the ability of wheat bran to regulate bowel function in the apparently healthy older adult may be accompanied by increased fecal calcium losses similar to what has been reported for younger adults.     

Rat bioassay of wheat bran folate and effects of intestinal bacteria

This study estimates the folate endogenous to a food material (wheat bran) and examines the role of intestinal bacteria in the rat bioassay for folate. After a 4-wk folate depletion period, rats were fed for an additional 4 wk basal diets with or without 0.5% phthalylsulfacetamide and with 100, 200 or 300 g of wheat bran; or 50, 100 or 150 g of xylan; or 0, 0.25, 0.50 or 0.75 mg of folic acid added per kg of basal diet. Xylan increased both liver and fecal folate, and this effect was nearly eliminated by phthalylsulfacetamide. Wheat bran contributed 1.6 micrograms of available folate per g of wheat bran without phthalylsulfacetamide in an apparently valid slope-ratio analysis. With the addition of phthalylsulfacetamide, liver folate increased in rats fed wheat bran diets and decreased in rats fed folic acid diets. The slope-ratio analysis for wheat bran folate with phthalylsulfacetamide became invalid due to a lack of intersection. Phthalylsulfacetamide had no effect on fecal folate excretion from rats fed the wheat bran diets. Further studies are needed on a variety of foods with and without phthalylsulfacetamide to evaluate the effect and importance of intestinal folate synthesis in the rat.     

The effect of wheat bran on the bioavailability of vitamin B-6 in young men

The effect of cooked wheat bran on the bioavailability of vitamin B-6 (B-6) was determined in 10 men, aged 20 to 35 years. The subjects consumed a constant diet with and without the addition of 15 g wheat bran during three successive 18-day periods in a switch-back design. Half of the subjects received the additional bran during periods 1 and 3; the other half consumed the bran during period 2. The bran and nonbran diets supplied, respectively, 1.69 and 1.66 mg of B-6 daily. Plasma total B-6 and pyridoxal phosphate (PLP), urinary 4-pyridoxic acid (4-PA), and urinary and fecal B-6 were determined at regular intervals during each period. Bran significantly increased fecal B-6 (P less than 0.05) and decreased urinary 4-PA (P less than 0.01). Bran also significantly depressed plasma B-6 (P less than 0.01) and PLP (P less than 0.05). These results indicate that the addition of 15 g of wheat bran to the diet decreased the bioavailability of B-6. Since this decrease was modest, never exceeding 17% (based on urinary 4PA and B-6), this amount of bran will not adversely affect B-6 status when intake of the vitamin is adequate.     

The effects of dietary fiber feeding on cholesterol metabolism in rats

The flux through the sterol biosynthetic pathway was studied in hepatocytes isolated from male Sprague-Dawley rats fed diets containing one of four fiber sources: cellulose, pectin, oat bran and wheat bran. Sterol synthesis measured by the incorporation of tritiated water or [2-14C]mevalonic acid was not inhibited in hepatocytes isolated from animals fed diets containing cellulose, pectin, oat bran or wheat bran when compared to animals fed a fiber-free diet. Based on these results, it is concluded that the intake of fiber has no inhibitory effect on endogenous sterol synthesis. In fact, in comparison to that in fiber-free controls, sterol synthesis was markedly elevated in pectin- and wheat bran-fed animals. In the case of the pectin-treated animals, the higher synthetic rate corresponded to an increase in 3-hydroxy-3-methylglutaryl coenzyme A reductase activity.     

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.     

Wheat bran and corn oil do not influence proliferation in the colon of healthy rats when energy intakes are equivalent.

Dietary intakes of fiber (wheat bran) and fat (corn oil) by rats were quantitatively varied for 6 wk while intakes of energy and essential nutrients were constant among the diets. The influence of wheat bran and corn oil levels on colonic epithelial cell proliferation was assessed using [3H]thymidine incorporation assays. Cellular proliferation in the cecum, proximal colon and distal colon was not significantly higher when healthy rats consumed low fiber in comparison to high fiber diets, nor when healthy rats consumed high fat diets in comparison to low fat diets. Additionally, there were no significant interactions between these variables. In comparison to the low fiber diets, diets high in fiber caused a significantly lower pH of luminal contents of the cecum and distal colon, but there were no significant differences in the total short-chain fatty acid concentrations of cecal digesta. These results suggest that when energy intakes are equivalent among diets, low levels of fiber or high levels of fat in the diet do not cause biological changes in colonic mucosa that may be associated with increased risk of colonic cancer.