7/30/2019 J. Nutr.-1983-Wrick-1464-79

1/16

The Influence of Dietary Fiber Source on HumanIntestinal Transit and Stool O utput1K. L. WRICK,2 J. B. ROBERTSON, P. J. VAN SOEST,B. A . LEWIS, J. M . RIVERS, D . A. ROEAND L. R. HACKLER3D ep artm en t of A nim al S cien ce, D iv isio n o f N utritio nalS cie nc es, C orn ell U niv ers ity , Ith ac a, N Y 1 48 53

ABS TRAC T Wheat bran ground to a coarse and fine particle size, purified cellulosea nd e th an ol-e xtra cte d c ab ba ge fib er, fe d to 2 4 a du lt m ale s d urin g a n 8 0-d ay m eta bo lictr ia l, w er e e xam in ed fo r e ff ec ts on in te stin al tr an si t t ime , ta xa tio n and s tool c ompos itio n.B rillia nt b lu e, p la stic p elle ts , p oly eth yle ne g ly co l (PEG )-4 00 0 a nd C r(III) m ord an te do nto iso la te d b ra n fib er w ere s im ulta ne ou sly a dm in is te re d fo r tra ns it m ea su reme nts .In te rs ub je ct v aria bility in re sp on se to fib er so urc e w as h ig hly s ig nific an t fo r a ll tra nsita nd s to ol m ea su reme nts. O nly c oa rs e b ra n o r c ellu lo se a dd itio n in cre ase d tra nsit s pe ed(d ec re as ed tra ns it tim e) o ve r b as al ra te s. G rin din g o f b ra n s ig nific an tly re du ce d fe ca lo utpu t beca use o f red uced fec al w ater. O nly su bjects con sum ing cellu lo se o r fin e branre po rte d d if fi cu lt o r uncom fo rta ble d ef ec ati on s. T hough c abbage p roduced th e smalle stfecal output, stools had a high m oisture content com parable to those obtained fromco arse b ran , w hic h su gg ests a larg e m icro bial o utpu t in respo nse to a ferm en tab le substra te . S ig nific an t n eg ativ e c orre la tio ns w ere p ro du ce d whe n c ha ng es in d ry m atte r o rcell w all in tak es w ere reg ressed w ith C r (III) tran sit. T hese fin ding s su gg est th at th ele ve l o f e ith er fo od o r fib er in th e d ie t a re v aria ble s th at in flu en ce in te stin al tra ns it tim ean d sh ou ld be con tro lle d in stu dies m easu ring it. In creases in fib er in tak e lin early increased fecal o utpu t o f w ater an d d ry m atter. R egressio n slo pes w ere ch aracteristic o feach fiber source. J. Nutr. 113: 1464-1479, 1983.INDEXING KEY WORDS fiber transit time stool output human

Investigations assessing the effects of di- norm al con trols. T ypes of disorders have var-etary fiber on m outh-to-anus transit tim e in ied w ithin experim ents and have includedhum ans have often yielded conflicting and, spastic colon, proctitis (10), constipation (8,h en ce , in co nc lu siv e re su lts. O nly a few o f th e 1 0, 1 1), d iv ertic ula r d ise as e (1 0, 1 2), d ia rrh eainvestigations reported successfully m ea- and irritable bowel syndrom e (11). The dif-sured digesta passage for those on controlled ferential passage of chrom ic oxide and poly-diets (1-3). W heat bran has been the main ethylene glycol (PEG) dem onstrated in sub-fiber source tested, though oat flakes (4), ba- jects w ith diverticular disease and choler-g asse (5 ), p urifie d c ellu lo se (6 ), g ua r g um (1 ), rh oe ic e nte ro pa th y (1 3) su gg ests th at a c erta inpectin (3, 7) and fruits and/or vegetables (1- disease state can affect m arker passage m ore4, 8, 9) w ere tested in som e studies. B agasse profoundly than any dietary variable.w as e ffe ctiv e in re du cin g tra nsit tim e, w he re as N ea rly a ll stu die s th at a llowe d se lf-se le cte dthe effect of orange fiber w as only slight (4), diets did not m ention a control for total leveland added cellulose or pectin had no effect, _which SUggestS that different fiber SOUrCeS 19SS American Institute of Nutrition. Received (or publication 29exert different effects on intestinal function. M arch983_. . n | . j , ' Supported in part by Department of Health. Education and Welfare,O ccasionally, m arker transit data trom sub- N ationalance rnstituterantOjects w ith g astrointestinal disturba nces w ere P resentddress:WoodhiiiBoad,ndov"MA018l?I*^ i r i i i Present address: Department of Foods and Nutrition. University of II-compared to those obtained from healthy, Hnou,rbana,Leisoi

1464

7/30/2019 J. Nutr.-1983-Wrick-1464-79

2/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 1465of food intake, which has consistently beena variable affecting rate of digesta passagein animals (14-18). Experiments in humansgenerally have not been designed to assessthe extent that intersubject variability, disease condition and the amount or composition of diet are factors affecting digesta passage rates in additi on to the presence of branor other f iber source.Studies of dietary fibers and their effectson bowel function have indicated variouschanges in stool output and composition, notall of which are solely attributable to water-binding properti es measurabl e in vitro ( 19) .Research reports examining the effects ofadded dietary fibers on stool bulk and composition have been reviewed (20), and it isgenerally agreed that fiber addition to anotherwise low fiber diet increases stool volume and improves taxation. This latter termis somewhat ill defined but usually refers tothe f requency and/or ease of defecati on.D ietary fiber isnot a uniform material andvaries widely in chemical composition andphysical properties with taxonomic class.Large dif ferences between intact vegetableand cereal f ibers and isolated cel lulose preparations have been reported for measurements of hydration capacity (21, 22), bulkvolume (22, 23) and fermentive capacity (24,25) . Variabil ity in physi cochemical properties permi ts speculation that the source, levelof intake and the bulk density (particle size)of dietary fiber consumed would alter therate of digesta passage, the total fecal outputof water and dry matter (DM ) , the frequencyof defecati on and the moisture content of thestool. These hypotheses were tested in a human metabol ic trial by using heal thy subjectswith no history of gastrointestinal disease. Ananalysis of present methods for mouth-to-anus transit time measurement and com-partmental turnover kinetics is presentedelsewhere (26 , 26a) .

MA TERIALSAND METHODSSubjects, diets a nd exper imenta l pla n

Other reports have presented the detailsof subject selection cri teria, selection, preparation and analysis of fiber sources, basaldiet composi tion and the statistical distribu

tion of diets (26-28). T he highlights of theconduct of the study are presented here.Fi ber sources used were white wheat branground to a coarse or fine particle size (R07-3691 Ameri can Associati on of Cereal Chemists, St. Paul, MM ) purified wood cellulose(SW -40 food grade Solka Floe, Brown Co.,Berl in, NH) and ethanol -extracted cabbagef iber (28). Particle size distributions and othercompositional data are presented in table 1.A ll fiber sources were baked into breads,which actually provided from 13-18 g of cellwall (CW ) daily [neutral detergent residue(NDR) or NDR plus pectin in the case ofcabbage fi ber] . Breads w ith added f iber weresubstituted for white bread in the basal diet,which contained approximately 1% NDR byanalysis. During the 80-day metabolic trial,the 12 subjects in group 1 changed fibersource with each 2-week experimental peri od, and the basal di et was given only duringperi od 5, the last period, extended to 3 weeksto account for delays in transit time. Sinceevery subject was fed each fiber source, theexperimental design was balanced acrossdiets to eliminate the effect of precedingtreatment. The 12 subjects of group 2 remained on the same fiber source for the duration of the study beginning with period 2.T he 2400-kcal diet proved insufficient tomaintain body weight i n many subjects. Calculated energy requirements based on individual weight loss data indicated a need toincrease caloric consumption by 0, 21, 42 or63% in selected subjects. T hese changes intotal dietary intake did not influence thechemical composition of the diet, and wereinstituted at period 4. During period 5, group2 doubled their fiber intake. T hough thesedietary changes were unanticipated at theoutset, they ultimately provided a means toexamine the effects of increasing DM andCW intake on transit and stool output measurements during periods 3-5. DM and CWconsumption were calculated for al l subjectsfrom diet homogenates collected and analyzed weekly.Stool collect ions

All feces were coll ected in a device similarto that described by Hinton et al. (29). Ontheir receipt at the metabolic unit, appro-

7/30/2019 J. Nutr.-1983-Wrick-1464-79

3/16

1466 WRICK ET AL.TABLE 1

An al ys is o f d ie ta r y fib er sCoarse bran Fine bran

P a rticle size, (% distr ibution by weight)> 2380 Mm 0.182380 > 1190 Mm 16.221190>590Mm 52.48590 > 297 Mm 28.92297 > 149 Mm 1.90149 > 74 Mm 0.19< 74 Mm 0.12

Geometric mean diameter, pm 744.4Geometric so, nm 1.671Chem ic a l c ompo si ti on o f fi be r sDry matter, % 91.1Cell wall, % NDR 44.0Hemicellulose, % 30.9Cellulose, % 9.3Lignin, % 3.3NDR content breads,2 % 13.6Phys ic a l p r op er t ie s o f fi be r sBulk volume:as fed, ml/g 3.3per unit NDR, ml/g 8.2Hydration capacity, ml/g NDR 3.5

Cellulose Cabbage

O0.020.0623.0449.0112.3015.58172.92.173

90.839.327.28.92.812.8

2.15.22.7

2.951.350.607.6346.6313.5627.27142.92.805

93.8100.02.696.50.117.8

13.013.91.4

0.16O40.9244.7010.492.051.68484.41.838

86.74 4 . 3 '7 .331.11.09.9'

4.712.320.71NDR value ( neutral detergent residue) excludes 29% pecti n. Total di etary f iber content of cabbage powder was73% and of cabbage bread 16.3%. 2 B asal diet white bread contained 1% dietary fiber.

priate data were recorded and samples wereweighed, f rozen and subsequently lyophi-l ized. Dried samples were seived through a2.36-mm screen to remove particulate markers. All 1650 samples were assayed individually for markers, none were pooled.The record of wet and dry stool weightspermitted calculation for each subject ofweekly outputs of total feces (TF) , DM , totalf ecal water (TFW) , the percent water content of stools and laxation rate, defined hereas the number of stools passed per week.Marke r s el ec ti on , admin is tr a t iona nd a na lysisA ll markers were given at breakfast ondays 1 and 7 of each period for al l subjects.During period 5, markers were given on days1, 7 and 17.Br illia n t b lu e. Su bje cts swa llowe d 1 00 mgof bri ll iant blue (F. D . & C. B lue No. 1 ,A l lied

Chemical, M orristown, NJ), a food coloringpreparation typical of dye markers used inhuman balance trials (30), in a gelatin capsulewithout added carboxymethylcellulose. Thetime of f irst fecal appearance was the onlydatum recorded, since the dye could not bequantitated in lyophilized stools.P EG . P EG (Union Ca rbide Chemica ls,New York, NY) with an approximate molecular weight of 4000 was diluted in water suchthat subjects ingested 1.0 g of marker foreach dose. Lyophilized stools were analyzedin duplicate by using the method of M alawarand Powell (31), by using a 2 mg:l gum ar-abic solution and a Bausch and Lomb 20spectrophotometer (Rochester, NY) with ared f il ter. A wavelength of 685 nm was usedsince the blue dye marker contributed ab-sorbance at 650 nm when present in f ecalf iltrates. A separate test indicated minimalinterference of the dye marker at this wavelength (27).

7/30/2019 J. Nutr.-1983-Wrick-1464-79

4/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 1467Ra diopa que pla stic pellets. P la stic pellets(Portex, L td., H ythe, K ent, England, CT 21-6JL ) such as those described by H inton et al.(29) were ingested in a dose of 25 each,packed in a gelatin capsule. L yophilizedstools were hand screened for pel let retrieval .Chromium-mordanted bra n CW. Thismarker, successful ly applied to ruminant di -gesta passage trials, has not been previouslyused in human intestinal transi t experiments.It was prepared by mordanting Cr (I II ) ontowheat bran CWs (32, 33) . Brief ly , starch- freecoarse or fine bran CW preparations werethoroughly washed with water, dried at 65,

soaked in a 10% (wt/vol) sodium dichromatesoluti on and kept at 100or 24 hours. Fiberswere washed and suspended in water acidified to pH 3.3 with ascorbic acid. The resulting greenish f ibers were washed, dried,and weighed into gelatin capsules such thateach dose provided 35-45 mg Cr.Chromium (I I I ) has an affinity for freehydroxyl groups present in CW cellulose orhemicel lulose, forming ei ther strong l igandsor other cross- links with them, such that theyare impervious to digestive or microbial enzymes. Chromium (II I) mordant preparations used in ruminant digestibility studieswere 100% recoverable on the fiber after72 hours of incubation with rumen microbes (32).

Coarse bran mordants were given to subjects on coarse bran diets, f ine bran mordantswere given to al l other diets because attemptsto attach Cr I I I onto cabbage f iber or puri fi edcellulose were unsuccessful. The amount ofbran fiber contributed by the markers wasless than 0.5 g each dose and was not expected to inf luence passage for those fed thenonbran diets.Fecal Cr recovery was assessed by atomicabsorption spectrophotometry (Perkin-ElmerM odel 305, Perkin-Elmer, Norwalk, CT,357.9 nm wavelength, 0.017 slit width, hollow cathode lamp and an ai r-acety lene f lame) .Fecal sample preparation required thatchromic oxide be solubilized, and involvedashing the dried sample, fusing the ash withpotassium nitrate crystals over a direct f lame,and dissolving fused samples in known quantities of distilled water (33). Samples wereappropriately diluted so that any Cr presentwas within the linear range of the standardcurve (0- 5 /ig/ml) .

C a lcula tion of tr ansit time indicesComplete passage of all markers did notoccur for several days fol low ing their inges

tion permitting analysis of excretion curvesfor the pellet, PEG, and Cr markers. A number of transit indices historically used in human and animal passage studies that werecalculated for the 730 admini stered markersare discussed separately (26) and include thetime to marker fi rst appearance (30), the timeto 80% recovery (29), mean transit time andcompartment turnover as estimated fromkinetic analysis of excretion curves (36). Thisreport is limited to the mean transit time(MTT ) for marker passage.The estimate of M TT represents the integrated average of a marker excretion curve.I t has been used in ruminant passage studies(33, 34), in small intestine transit studies inhumans that used mul tiple indicator di lutiontechniques (35) and several dietary fiberstudies in humans (1, 3, 9, 27, 37). T he equation is:

where t, is the time between marker administration and the ith defecation, and M , is theamount of marker in the fth defecation.St at is tic a l a n a lys is

The SAS General L inear Models procedure(38), a form of multiple linear regression on0,1 variables (39) was used to analyze themarker passage data collected on group 1subjects. Tradi tional analysis of variance procedures would not lend themselves to an unbalanced data matrix, i.e., one which hadoccasional missing values. A linear modelapproach f its the experimental observationsto a regression equation, which in turn canbe used to estimate or predict a result whenthe effects of one or more factors are removed. This statistical approach was morerigorous in that known sources of experimental variability, such as the effects fromsubject, experimental period, or carryovereffect from the previous diet, were statistically quantified and removed from the effects of fiber source, the dietary variable ofspecial interest.An R2 value calculated along w ith typicalanalysis of variance statistics served as a cor-

7/30/2019 J. Nutr.-1983-Wrick-1464-79

5/16

1468 WRICK ET AL.relation coef ficient between the estimatespredicted by the equation and the actual observations used to derive it. The Rz can beviewed as an estimator of how wel l the dataf it a l inear model and isreported in al l of theanalysis results.Analysis of variance was performed ondata f rom group 1 subjects only. The orderof presentation of diets to group 2 did notpermit a statistical analysis by this means.

RESULTSMa rker r ecover y. Mea n r ecover y for 242doses of l g PEG was 85.3 12.6%. Theprocedure used was designed for analysis ofintestinal perfusates and may not be ade

quate for rehydrated fecal material. Recovery of a known amount of PEG added tofecal material prior to lyophi lizing rangedf rom 68-72%. Other investigators have reported diff icul ties in recovering PEG fromdried feces, noting that it can associate withparticulate matter if samples are frozen (36).Recovery f rom cow feces has ranged f rom40-60% (40) and in vitro tests (41) have reported adsorption of PEG onto vegetable f ibers even after centrifuging at 14,000 X gfor 1 hour.A signi ficantly low recovery of PEG wasfound for group 1 subjects consuming cabbage (P = 0.05) compared to the recoveryof the marker when the basal diet was fed.This suggests that the f iber composition ofthe diet may inf luence the recovery of a water-soluble marker. The microbial populationinduced by cabbage fiber consumption mightproduce bacterial cel l wal ls of a di fferentnature capable of binding the marker in ly-ophi lized stools. I f so, PEG binding by stoolcomponents could interfere with solubiliza-tion and filtration of the marker during analysis, causing low recoveries.M ean recovery of 244 administrations ofradiopaque plastic pellets was 98.2 3.5%.Recoveries other than 100% could be attributed to ei ther miscounting during markerpreparation or recovery, or fracture duringhandl ing of some very hard, compact stoolsamples. Stools from subjects consuming cellulose lacked the friable characteristics ofthose consuming bran, and had to be hammered in order to break them into smaller

pieces for pellet retrieval. Pellet recovery wassignificantly lower in stools from cellulosediets (P = 0.02) compared to recovery whenthe basal diet was fed. Recoveries were signifi cantly influenced by subject eff ects(P = 0.02).M ean fecal Cr recovery from 244 doses ofCr-mordanted bran was 84.0 16.9%. Recovery of potassium dichromate standardsaveraged 93.2%, with a coef ficient of variation of 6%. Incomplete conversion to chromic-oxide and occasional marker overlap betweenperiods are explanations for results otherthan 100%.Cr recoveries from group 1 subjects werenot inf luenced by intersubject variabi li ty .However, analysis of Cr recoveries duringperiods 1-4 revealed a significant carryovereffect f rom a previous diet of cellulose (P= 0.03), which significantly depressed Cr recovery during the fol lowing experimentalperiod, regardless of what new fiber sourcewas fed. The reason behind this observationis not clear. A possible explanation might bethat cellulose sufficiently altered the coloniemicrof lora such that there was a microbialinteraction with the mordant, which somehow influenced recovery of the metal.There were no significant effects of subject,period, previous diet or f iber source on thetime for f irst appearance in feces of brill iantblue. The fai lure of dye markers to be quantifiable in feces precludes their usefulness intransit studies.Exper imen ta l va r i abl es i nfl uenc ing marke rtr a nsit a nd stool output. The levels of significance of subject, period, previous diet andfiber source effects on transit and stool outputare listed in table 2. Intersubject differenceswere highly significant as was variation dueto fiber source. Analysis of stool output dataf rom periods 1-3 are shown because a separate analysis indicated a strong period effect(P < 0.0004) f rom the increase in intake imposed at period 4. Previous diet effects weresignificant only for the water content of thestool. R2 values range from 0.57 to 0.88, asmight be expected for biological data, andsuggest these data f it a l inear equation reasonably well.The a ddition of differ ent fiber sour ces toa low fib er , b as al d ie t (ta ble 3 ). A c omp ar iso nof transit time and stool output data from

7/30/2019 J. Nutr.-1983-Wrick-1464-79

6/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 1469TABLE 2

Significa nce of exper imenta l va ria bles influencing ma rker tr ansit time (MTT)a nd stool output in group 1 subjects

MT T (periods-4)PelletsPEGCr-mordantStool

output per week (periods-3)2TF.gDM,gTFW,gLaxationrate,efecationsStoolwater content, %R20.720.570.790.710.670.730.750.88Subject0.00010.00010.00010.00010.00040.00010.00010.0001Period

PreviousietProbability0.070.060.002'0.740.390.800.620.25ofa g r ea te r0.760.990.700.970.550.920.660.05Fiber

source0.0020.010.0020.00010.0001

1The signi fi cant peri od ef fect was shown in a separate anal ysi s to be f rom the increase in di etary intake imposedat period 4. 2 A nalysis excludes period 4 data because of the significant (P < 0.0004) intake effects present foral l output measurements except taxation rate.

diets containing fiber and the low fiber basaldiet was made on group 1 data, periods 1-5.Because the basal diet was fed exclusivelyduring period 5, data were corrected for effects of subject and diet only and were testedagainst the basal diet for significance.Coarse bran and cel lulose provided thefastest transit, regardless of marker type. TheMTT values obtained from fine bran andcabbage diets were not significantly differentfrom those obtained on the basal diet. A separate analysis of data from periods 1 to 4corrected transit observations for previous

diet and experimental period effects. Regardless of marker type, only coarse bran andcellulose provided significantly faster transittimes than cabbage (0.0005 < P

7/30/2019 J. Nutr.-1983-Wrick-1464-79

7/16

1470 WRICK ET ALbage fibers provided stoolsof higher moisturecontent than did the basal diet alone. Complaints of diff iculty in passage of hard stoolswere confined to the subjects consuming cellulose and fine bran.To compare the ef fects of di ff erent f ibersources without the influence of increaseddietary intake, data from periods 1-3, forgroup 1 subjects were separately analyzed,and fiber sources were tested against cabbagefor significance. Only subject and diet effectswere signif icant, carryover effects from theprevious diet were not. Relative to cabbagef iber, coarse bran and cel lulose f ibers provided significantly greater taxation rates andoutputs of TF, DM and TFW . Fine branprovided a significantly larger output of TFand DM but stools of a signifi cantly lowermoisture content than the cabbage fiber.P a r tic le size e ffe cts. Tr a nsit a nd sto ol o utput data from the two bran diets were examined in a separate l inear model and analysis for group 1 subjects. As shown in table4, coarse bran provided significantly fastermarker passage than f inely ground bran regardless of marker type, confirming the dataof K irwan et al. (42) and H eller et al. (27).These authors found significant particle sizeeffects on intestinal transit time using a lessrigorous statistical analysis. Fine-grindingcaused a reduced bulking ef fect because asmal ler volume of the colon was occupied.

Fermentation data revealed no effect ofgrinding on fermenlability in vitro (43).Coarse bran produced significantly greaterstool outputs of higher moisture content.C ompa rison of br an a nd cellulose fiber s.( table 5) Subjects fed coarse bran producedstools of significantly greater water content,and outputs of TF and TFW were also higherthan stools from subjects fed cellulose. Thetaxation rate and DM outputs were not signi ficantly di ff erent. A comparison of datafrom subjects consuming f ine bran and cellulose was made because of the particle sizedifference present between coarse bran andcellulose fibers. No significant differenceswere found for any of the stool measurements.

Mar ke r c omp ar iso n. A s ep ar a te a na lysis o fMTT values from al l 3 markers from group1 subjects, periods 1-4, revealed no significant differences in transit time estimates between marker types. Data were corrected foreffects of subject, period, previous diet andfiber source.Changes in tota l food (DM) and fiber(CW) inta ke levels. C a lcula tio ns o f weeklyintakes of DM and CW permitted examination of the effects of increasing fiber intakeon transit time and fecal output by linearregression analysis. Appropriate regressionstatistics derived f rom relating ei ther DMintake to Cr-MTT, or CW intake to Cr-MTT,

TABLE 4Br a n pa r ticle size effe cts o n ma r ker tr a nsit a nd sto ol o utp ut fo r gr ou p 1 s ub jec ts '-2Coarse bran Fine bran

M ean transitimePellets,hrPEG,hrCr-mordant,hrStooloutputTotalfcesTF),Drymatter (DM),Total

fecal water (TFW),Laxationrate,efecationsStoolwater content, %18.1'47.7'26.7"953"219733"6.678.5'34.056.442.58312096225.674.94.78.45.046.89.638.50.70.90.840.490.820.' Transit data from periods 1-4 were analyzed, whereas stooloutput data from periods 1-3 were analyzed becauseof the signi ficant intake ef fect (P = 0.0001) on al l measurements when period 4 was included. 2Intersubjectvariabil ity was signif icant for all measurements (P < 0.005) except stool dry matter content. eans are significantly di fferent (P < 0.03) f rom fine bran.

7/30/2019 J. Nutr.-1983-Wrick-1464-79

8/16

FIBER SOURCE, TRANSIT T IME AND STOOL OUTPUT 1471TABLE 5

Compa rison of coa rse br an a nd cellulose effects on stool composition a nd ta xa tion ra tefor gr oup subjects, per io ds l-3lWeekly outputs

Total feces(TF) Dry matter(DM) Total fecalwater ( TFW) L axationrate3 Stool watercontent

CoarseranCelluloseSEMfi 2958'80849.80.8322021011.90.69737"59839.40.866.26.20.560.8977.8"73.90.710.86

1Anal ysi s excludes data f rom period 4 when increases in di etary intake were imposed. 2 In tersubj ect vari abi li tyw as si gnifi cant ( P < 0.05). 3Me asured as defecati ons. ' M eans are signi fi cantly di ff erent from cel lul ose (0.001< P < 0.01).

outputs of TF, TFW, DM, water content andtaxation rate are shown in tables 6 and 7,respectively. Data for periods 3-5 were usedfrom al l 24 subjects. These periods were selected because they represented the broadestspectrum of f iber intakes, i .e., the total dietincreases of 0, 21, 42 or 63% beginning atperiod 4, the basal level of intake for group1 during period 5, and the approximate doubl ing of f iber intake level for group 2 duringperiod 5. Of the seven sets of regressions performed, those providing significant regression equations are plotted in f igures 1-6. Al lare discussed in greater detail below.DM inta ke and Cr -MTT. The da shedregression l ine in f igure 1 shows a sig

nificant decrease in C r-MTT as DM intake increases, regardless of diet type.T hese data predict a 7- to 8-hour decrease in M TT with each 100-g increasein total DM intake. When transit datafrom individual diets were examined,only f ine bran showed a signi ficantlynegative regression slope, though coarsebran, cabbage and the low f iber basaldiets showed negative trends in the data.The negative trend on the low fiber basaldiet is of interest because CW intakeswere maintained between 3.5 and 5.0g per day, despite an increase in DMintake of over 30% in some subjects. Theexception to these trends was the cellulose diet, which showed a distinct

TABLE 6Regression ana lysis of dry ma tter (DM) intake on Cr -MTT for 24 subjects, per iods 3-5 '

Change in Cr-M T T with increasing DM intakeCorrelationorAlldietsCoarsebranFinebranCelluloseCabbageBasaldf7113141413 9Correlation

coeff.r)-0.32-0.24-0.62+0.36-0.35

-0.17P0.01NS0.01NSNNSRegression

slopeb)-0.08-0.12t P (b *)-2.780.02-2.90

0.05Intercept105.6128.4

' A bbreviations as fol low s: df, degrees of freedom; r, correlation coeffi ci ent; P, level of si gni ficance of r; t, tstati sti c; P( b & 0) , l evel of si gni fi cance of t f or regression slope unequal to zero; NS, not signi fi cant.

7/30/2019 J. Nutr.-1983-Wrick-1464-79

9/16

1472 WRICK ETL.TABLE7Regression

a na lysis o f c ell wa ll (CW) in ta ke le ve ls on ta xa tio n r a te a nd sto ol c omp os itio nfo r 2 4 su bjec ts, p er io ds 3-5Correlation

of CW intakes:1.Cr-MTTAlldietsCoarsebranFinebranCelluloseCabbage2.

Total fecalutputAlldietsCoarsebran2Finebran2CelluloseCabbage3.

Dry matterutputAlldietsCoarsebran3Finebran3Cellulose3Cabbage4.

Total fecalaterAlldietsCoarsebran2FinebranCelluloseCabbage5.

LaxationateAlldietsCoarsebranFinebranCelluloseCabbage6.

Percent waterontentAlldietsCoarsebranFinebranCelluloseCabbagedf711314141387171618198717161719861616171682171616158617161718r-0.20-0.48-0.58+0.02-0.610.770.780.80

(b)-1.50-2.63-5.7140.7451.0054.2639.109.611.616.911.45.431.138.842.3)0.010.020.020.010.010.010.010.010.010.

1Abbreviations asfollows:df, degrees of freedom; r, correlation coefficient; P, level of significance of r; t, t statistic;P (b & 0 ) level o f sig nific an ce o f /, fo r r eg re ssio n slop e u neq ua l to ze ro ; NS, n ot sig nific an t. 2 R eg res sio n slo pesignif icantly greater than cellulose (P < 0.01). 3Regression slope signif icantly greater than cabbage (P < 0.01).

though not significant tendency for anincrease in Cr-MTT with an increase inDM intake.CW intake and Cr -MTT. The regr ession plots relating CW intake to Cr-MTT showed similar results to those of

D M intake (fig. 2). An increase in CWintake from all sources showed a significant decrease in Cr-M T T. T hese datapredict a 7- to 8-hour decrease in M T Twith each 5-g increase in CW intake.Regression of Cr-M TT on CW intakef rom individual diets resulted in signif -

7/30/2019 J. Nutr.-1983-Wrick-1464-79

10/16

FIBER SOURCE, TRANSIT TIM E AND STOOL OUTPUT 1473140

120100

-z 80c .

60

40

20

LF B

a ll d a ta

CB

400 5 )0 60 0Dry M atte r In ta ke , g /w k

700 800

Fig. l Change in Cr transi t time with increasing dry matter intakes. ,CB (coarse bran) ; O, FB (fine bran) ;A, Ca (cabbage); V, Ce (cellulose); D, LFB (basal diet) . Regression slopes for all data and FB were signif icantlygreater than zero (P s 0.05). Dotted lines indicate trends (not significant) for respective diets.

icant negative slopes for f ine bran andcabbage. The steep negative slope obtained for cabbage fiber impli es thatvegetable matter is the most ef fectivefiber source in reducing transit timewith only slight increases in CW intake.However, the 10-12 g of cabbage f iberconsumed in this study, equivalent to 2.2kg of fresh cabbage daily, providedM TT values of approximately 100 hours,ranking it as the fiber source least effective in reducing transit. These datapredict that a steady consumption ofabout 200 g of fresh cabbage daily(about 2.5 g of dietary fiber) for 10 to14 days would have provided an MTTof about 144 hours or 6 days. C learly,vegetable fibers at levels commonly consumed contribute l ittle to speed of di -gesta passage.

CW intake and TF output (fig. 3). A nincrease in CW intake from all fibersources correlated with an increased TFoutput. Significant positive correlationsand regression slopes were obtained fordiets containing coarse bran, f ine branand cel lulose but not for the cabbagediet, though a trend for increased outputwas present in these data. Regressionslopes in table 1 predict the expectedincrease in output of feces per gram ofCW consumed.CW intake and DM output (fig. 4) . Significant positive correlation coefficientsand regression slopes were obtainedwhen DM outputs from all experimentaldiets were regressed collectively or individually against CW intake level. Predicted increases in DM output with each

7/30/2019 J. Nutr.-1983-Wrick-1464-79

11/16

1474 WRICK ET A L14 0

12 0

100

- 80

to40

2 0

Ce

a nda taC B

10 15 20 25 30C e ll W all In ta ke , g /w k

35 4 0 45Fig. 2 Change in Cr transit with increasing fiber intake. ,CB (coarse bran); O, FB (fine bran); A, Ca (cabbage);V, Ce (cellulose);D , basal diet. Regression slopes are signif icantly greater than zero (P -g 1 2 0 0a -

o 1 0 0 0 800

60 0

40 020 0

0 10 15 20 25C ell Wa ll Inta ke , g /w k

30 35Fig. 3(cabbage)for cabbagi

Change in fecal output with increasing cell wall intakes. ,CB (coarse bran) ; O , FB ( fine bran) ; A , CaV, Ce (cellulose); D, basal diet. All regression slopes are significantly greater than zero, (P = 0.01) except;e(dotted line).

7/30/2019 J. Nutr.-1983-Wrick-1464-79

12/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 1475500

400

5f300oe.200100

Ce

10 15 20Ce l lWa l l I n ta k e , g /wk 25 3 0 35Fig. 4 Change in dry matter output w ith increasing cel l wal l intake. ,CB (coarse bran) ; O, FB (fine bran) ;A, Ca (cabbage); V, Ce (cellulose); D, basal diet. All regression slopes are significantly greater than zero (P

7/30/2019 J. Nutr.-1983-Wrick-1464-79

13/16

1476 WRICK ET AL.1312111098765432l

CDO00 0

00 o

10 15 20 25 30CellWallIntake,g/wk

35 40 45 50Fig. 6 Change in laxation rate with increasing cel l wal l intakes. CB (coarse bran) ; O, FB (fine bran) ; A, Ca(cabbage); V, Ce (cellulose); D, basal diet. Regression slopesare significantly greater than zero (P 0.02) for Ce,Ca, and al l data.

from all experimental diets against CWintake level produced a significant positive correlation and regression slope,which predicted an increase of 31 g ofwater output with each additional gramof CW intake. Significant positive correlations and regression slopes were alsoobtained for all fiber sources except cabbage, in spite of the high moisture content present in the stools produced fromthat diet.CW intake and laxation rate ( fig. 6) . Anincrease in CW intake correlated significantly with an increase in laxationrate when data f rom al l experimentaldiets were collectively analyzed (regression slope b = 0.13). Regression analysisof laxation rates f rom individual f ibersources revealed that increased intakesof ei ther coarse or f ine bran did not significantly increase the number of stoolsper week. A positive correlation was obtained between an increase in either cellulose or cabbage f iber intake and laxation rate; however, the rate of increaseper gram of fiber consumed was lessthan one stool per week.CW intake and percent water contentof stools. A change of fiber intake did

not correlate with any change in thepercent water composition of feces forany fiber source except fine bran, whichproduced a positive regression slope.DISCUSSION

The effects of fiber source on mean transittime reported here clearly support the hypothesis that dietary fiber will provide fasterpassage of digesta residues than a diet f reeof or extremely low in f iber, but this conclusion cannot be extended to all f iber sources.The f inding that coarse bran behaves sodifferently from vegetable fiber supports theconclusions of Cummings et al . (1) , who reported different responses in colonie functionwhen bran, apple, carrot, cabbage and guargum were fed under control led conditions.Our f indings are in concert with the expectation that noncrystalline cellulose and pectin, predominant in cabbage fiber, are readilyfermented in the colon, causing considerableloss of bulk. Fiber digestibilities calculatedfor these subjects averaged 75% for cabbageCW, 52% for cabbage hemicellulose and 82%for cabbage cellulose (43). These CW andcellulose digestibility coefficients were thehighest of al l f iber sources fed, despite thehigh level consumed (equivalent of 2 kg freshcabbage daily).

7/30/2019 J. Nutr.-1983-Wrick-1464-79

14/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 1477Solka Floe behaved similarly to coarsebran. Purified cellulose has no CW structure,but i ts high bulk volume despi te smal l particle size was responsible for itseffect on transit. I ts relative nonfermentabi li ty was confirmed by the consistently negative trends indigestibility coefficients in group 2 subjectswho consumed cel lulose as the sole fibersource for 66 days (43).Addition of dietary fibers to a low fiberdiet increased fecal outputs of water and DMto variable extents depending on the f ibersource. A fiber source of a sufficiently largeparticle size to insure an intact CW structureand sufficient lignification to resist extensivefermentation of CW constituents is the mosteffective in promoting bulkier stools of high

moisture content. Coarse bran met these requirements in this investigation and insuredmore frequent defecations. Fine grindingdiminished all these characteristics as mightbe predicted by the reduced bulk volume andhydration capaci ty observed in vi tro. Thisf inding confirms earlier reports regardingparticle size ef fects on stool weight (27, 42,44). Also of interest was the observation thatcellulose and fine bran influenced stool output similarly, probably because of their comparable particle size. The remarkable exception was the difference in stool water content.Relative to the other f ibers tested, f ine branproduced stools of the lowest moisture content, a surprising result in light of a waterholding capaci ty greater than that for cellulose in vi tro. The signi ficant increase instool water content with coarse bran reportedhere refutes several earlier observations (44-46), perhaps because the large intersubjectvariability inherent to human studies maskedfiber particle size effects on stool water composi tion in these reports. The f inding thatlarger, bulkier, moister stools were producedwith the coarse bran in this study has therapeutic implications for constipated patients.Cabbage fiber was fermented so extensively(28) that its influence on fecal output wasconsiderably less than that of coarse bran,and compared closely with the basal diet.Fiber source effects on stool compositionand laxation rates are of interest because theydo not parallel the effects of transit time.Coarse bran provided the fastest transi t inthis study, followed by cellulose and finebran. Transit times on the cabbage diet were

not significantly different from those on thebasal diet. In spi te of low fecal outputs andslow transit, cabbage fiber matched coarsebran in stool water content.These observations suggest several points:1. Stool water content isa function of f ibersource, not transit time, and is generally uninfluenced by fiber level.2. Delayed transit times do not assure thepassage of hard dry stools. Though coloniersorptionmechanisms theoretically havemore time to dehydrate colon contents, vegetable f ibers induce a suf ficiently large mi-crobial mass that is i tsel f high in water unavailable for absorption.3. D if ferent f iber sources serve as stoolsofteners by different means. V egetable fiberinduces the formation of microbial cells highin moisture content by virtue of its extensivefermentation. Coarse bran also induces theformation of a microbial mass by fermentation, but to a lesser extent and maintainsa sufficient CW structure, because of the lig-nin present, to entrap water.4. Comfortable laxation is a function ofstool water content and/or f iber particle sizerather than fecal bulk. Coarse bran providedthe greatest fecal output and cabbage thelowest, but nei ther were reported to causethe hard, dry, diff icult- to-pass stools associated with constipation. Such laxation diff icul ties were conf ined to the cel lulose andfine bran fibers. Apparently ease of defecation is not a function of transit time.Stool moisture variations alone are not sufficient evidence that fiber induces microbialgrowth in response to a fermentable substrate. Increased cabbage fiber consumptionin group 2 subjects, equivalent to over 4 kgof fresh cabbage daily did not significantlyincrease fecal mass (figure 3), but was foundto dramatically increase fecal nitrogen content (43). Fecal nitrogen was least influencedby cellulose, the least fermentable fiber (28).

Only traces of dietary nitrogen are expectedto escape upper tract absorption, and microbes are capable of incorporating nonpro-tein nitrogen into their own cell mass. Thesefindings support the assumption that different fiber sources influence stool compositionas regards moisture and microbial cells.T he data in figures 1 and 2 suggest thatthe total food and/or f iber intake levels are

7/30/2019 J. Nutr.-1983-Wrick-1464-79

15/16

1478 WRICK ET A L.variables that can significantly influence di-gesta passage and that should be controlledin prudently designed studies that measurehuman intestinal transi t or involve the useof indigestible markers. Negative relationships between digesta passage rates and foodintake levels have been reported in experimental animals (14-18). The data for purified cellulose suggest anomalous behavior relative to other f iber sources with intact CWstructures. This observation warrants furtherstudy, especially if purified cellulose preparations are to be considered as a means of"fortifying" foods commercially.The simi lar behavior of the pel lets, PEGand Cr markers suggests that solid and liquidphases of digesta pass through the humandigestive tract in comparable fashion. Find-lay et al. (13) also found nearly identical passage rates for Cr2Os and PEG in one humansubject free of intestinal disease. Togetherthese results suggest that, provided dietaryintake is controlled, any one of the threemarkers studied can be used to measure human intestinal MTT , which can be considered an indicator of total tract passage time.Discussions regarding the preference for anyone marker for use in gastrointestinal kineticstudies that estimate digesta retention timesin individual digestive compartments arepresented elsewhere (26, 26a).

ACKNOWLEDGMENTSThe authors wish to thank Dr. Stephen N.Heller, General M ills, Inc., M inneapolis, M Nand Dr. Peter Uden, the Agricultural Collegeof Sweden, Upsala, Sweden for thei r assistance in marker analysis. We appreciate thehelp of Dr. Lucille Stiles, Research Dietitian,and D r. W alter Federer, D epartment ofBiometry and Plant Breeding, Cornel l University for statistical consultation. M s. M aureen Taupley provided untiring assistance inprocessing biological samples. The computer

facilities and programming assistance of Dr.James G. Oakes, the Raytheon Corporation,Northboro, M A, is gratefully acknowledged.L ITERATURE C ITED

1. Cummings, J. H ., B ranch, W ., Jenkins, D . J. A .,Southgate, D. A. T., Houston, H. & James, W. P. T.

(1978) Colonie response todietary fibre from carrot,cabbage, apple, bran, and guar gum. Lancet 1, 5-8.2 . Kelsay ,J. L ., Behal l, K . M . & Prather, E . S. (1978)Effect of fiber from fruits and vegetables on metabolic responses of human subjects. I. Bowel transittimes, number of defecations, fecal weight, urinaryexcretions of energy and nitrogen, and apparentdigestibi li ties of energy, ni trogen and fat. Am. J.Clin. Nutr. 31, 1149-1153.3. Stasse-Woltheus, M., Albers, H. F. F., Van Jeveren,J. G. C., dejong, J. W. , Hautvast, J. G. A. , Hermus,R . J. J., Katan, M . B ., B rydon, W. G . & Eastwood,M . A . (1980) Inf luence of dietary f iber f rom vegetables and frui ts, bran or ci trus pectin on serumlipids, fecal lipids, and colonie function. Am. J. Clin.Nutr. 33, 1745-1756.4. Wal ker, A . R. P. ( 1975) E ff ect of hi gh crude fi berintake on transit time and the absorption of nutrientsin South African Negro children. Am. J. Clin. Nutr.28 , 1161 -1169.5. W alters, R. L ., Baird, I . M ., D avies, P. S., H ill,M . J., D rasar, B . S., Southgate, D . A . T ., G reen, J.& Morgan, B. (1975) Effects of two types of dietary fibre on fecal steroid and lipid excretion. Brit.Med. J. 2, 536-538.6. Eastwood, M. A. , Kirkpatrick, J. P. , Mi tchel l, W. D. ,Bone, A. & Hamil ton, T. (1973) Effectsof dietarysupplements of wheat bran and cellulose on fecesand bowel function. Bri t. Med. J. 4, 392-394.7. Durrington, P. N ., Manning, A . P., Bot n,H . C.& Hartog, M . (1976) Effect of pectin on serumlipids and lipoproteins, whole-gut transit time, andstool weight. Lancet 2, 394.8. Cowgill, G. R. & Sullivan, A . J. (1933) Furtherstudies on the use of wheat bran asa laxative. J. Am.M ed. Assoc. 100, 795-802.9. Parks, T . G. (1973) T he effects of low and highresidue diets on the rate of transit and compositionof the faeces. Proceedings Fourth International Symposium on Gastro-Intestinal M otility, pp. 369-380,M itchell Press, Vancouver, B. C.10. Paylor, D . K ., Pomare, E. W ., H eaton, K . W . &Harvey, R. F. ( 1975) The ef fect of wheat bran onintestinal transit t ime. Gut 16, 209.11. H arvey, R. F., Pomare, E. W ., & H eaton, K . W .(1973) Effectsof increased dietary fibre on boweltransit. Lancet 1, 1278-1280.12. Findl ay, J. M . , Smith, A . N ., M i tchel l, W . D ., Anderson, A . J. B . & Eastwood, M . A . (1974) E ffectsof unprocessed bran on colon function in normalsubjects and in diverticular disease. Lancet I, 146-149.13. Findl ay, J. M . , M i tchel l, W . D ., Eastwood, M . A .,Anderson, A.J. B*& Smith, A. N. (1974) Intestinalstreaming patterns in cholerrhoeic enteropathy anddiverticular disease. Gut 15, 207-212.14. Castl e, E. J. ( 1956) The rate of passage of f oodstuffsthrough the alimentary tract of goats. I. Studieson adult animals fed hay and concentrates. Brit. J.Nutr. 10, 15-23.15. Coombe, J. B . & Kay, R . N . B . ( 1965) Passage ofdigesta through the intestines of sheep. Retentiontimes in the small and large intestine. Brit. J. Nutr.19, 325-338.

7/30/2019 J. Nutr.-1983-Wrick-1464-79

16/16

FIBER SOURCE, TRANSI T T IME AND STOOL OUTPUT 147916. Grovum, W . L. & W illiams, V . J. (1973) Rate ofpassage of digesta in sheep. 3. D if ferenti al rates ofpassage of water and dry matter f rom the reti culo-rumen, abomasum and caecum, and prox imal colon.B ri t. J. Nutr. 30, 231- 240.17. Grovum, W . L. & Hecker, J. F. (1973) Rate ofpassage in sheep. 2. T he effect of food intake ondigesta retention times and on water and electrolyteabsorpti on in the large intestine. Brit. J. N utr. 30,221-230.18. Grovum, W . L. & W illiams, V . J. (1977) Rate ofpassage of digesta in sheep. 6. The ef fect of l evel offood intake on mathemati cal predi cti ons of the kineti cs of digesti on in the reti culo- rumen and intesti nes. B ri t. J. Nutr. 38 , 425- 436.19. Stephen, A . M . & Cummings, J. H . (1979) W ater-holding by dietary f ibre in v itro and i ts relationshipto faecal output in man. Gut 20, 722-729.20. K el say, J. L . ( 1978) A revi ew of research on ef fectsof fiber intake in man. Am. J. Clin. N utr. 31, S142-S159.21. Eastwood, M . A . & M itchell, W . D . (1976) Thephysiological properties of dietary f iber: a biologicalevaluati on. I n: Fi ber i n Human Nutri ti on (Spi ll er,G. A . & A men, R. J., eds.), pp. 109-130, PlenumPress, New York .22. V an Soest, P. J. & Robertson,]. B. (1976) Chemicaland physi cal properti es of di etary f iber. I n: D i etaryFibre (H awkins, W . W ., ed.), Proc. M iles Symposium, pp. 13- 25, N utrition Soci ety of C anada, D al-housie Universi ty , Hal if ax , N .S.23. V an Soest, P. J. (1975) Physico- chemical aspectsof f ibre di gestion. I n: Proceedings of the Fourth I nternati onal Symposium on Rumi nant Physi ology(M cD onald, I . W . & W arner, A . C. I ., eds.), pp. 351-365, U niversity of N ew England Publishing U nit,Armidale, N.S.W., Austral ia.24. V an Soest, P. J. & M cQueen, R. W . (1973) Thechemi stry and estimati on of fi bre. Proc. Nutr. Soc.32, 123-129.25. Goering, H. K ., & V an Soest, P. J. (1970) Foragef iber analyses (apparatus, reagents, procedures andsome appli cati ons). A grie. H andb. No. 379, pp. 12-15, ARS, USDA , Washi ngton, DC.26. W rick, K . L. F. (1979) The influence of dietaryf ibers on intestinal passage, taxation and stool character istics in humans. Ph.D. thesis, Cornel l Universi ty, I thaca, NY .26a.V an Soest, P. J., Uden, P. & W rick, K . L. (1983)Critique and evaluation of markers for use in humans and f arm and l aboratory animals. N utr. R ep.I nt. 27, 17- 28 .27. H el ler, S. N ., H ackl er, L . R ., R ivers, J. M . , V an Soest,P. J., Roe, D . A., Lewis, B. A . & Robertson, J. B.(1980) D ietary fiber: the effect of particle size ofwheat bran on coloni e f uncti on in young adul t men.Am. J. C li n. N utr. 33, 1734-1744.28. Ehle, F. R., Robertson, J. B. & V an Soest, P. J.( 1982) I nf luence of di etary f ibers on f ermentati onin the human large intesti ne. J. Nutr. 112, 1 58- 166.29. H inton, J. M ., L ennard-Jones, J. E. & Y oung, A . C.( 1969) A new method for studying gut transit timeusing radiopaque markers. Gut 10, 842 -847.30. Lutwak, L. & Burton, B. T. (1964) Fecal dye

markers in metabol ic bal ance studi es. Am. J. C li n.Nutr. 14, 109- 111.31. M alawar, S. J. & Powell, D . W . (1967) An improved turbidimetric analysis of polyethylene glycoluti li zi ng an emulsi fi er. Gastroenterology 53, 250-256.32. M artz, F. A ., V an Soest, P. J., Bogt, J. R. & H ilde-brand, E. S. (1974) U se of elemental tracers andactivation analysis in digestion, rate of digesta f lowand food particle tracking studies in cattle. Proceedings Sixth Symposium Energy Metabol ism , European Association of Animal Production. Pubi . No.14, pp. 111- 114, Stuttgart, West Germany.33. U den, P., Colucci, P. E. & V an Soest, P. J. (1980)I nvestigation of chromium, cerium and cobalt asmarkers in digesta rate of passage studies. J. Sci.Food Agri e. 31, 625- 632.34. Blaxter, K. L., Graham, N. M cC. & Wainman,F. W . (1956) Some observations on the digestibility of food by sheep, and on related problems.B rit. J. N utr. 10, 69- 91.35. L agerl f, H . O. (1976) M athematical analysis ofindicator concentration time curves obtained in systems w ith constant or varyi ng mean transi t times.M t Sinai J. M ed. 43, 9-20.36. V an Soest, P. J. (1982) Anal yti cal systems for evaluati on of seeds; and The kinetics of di gestion. I n:Nutri ti onal Ecology of the Ruminant, pp. 75- 94 and211-229, O & B Books I nc., Corvallis, OR.37. Cummings, J. H., Jenkins, D . J. A . & W iggins,H. S. (1976) M easurement of mean transit timeof dietary residue through the human gut. Gut 17,210-218.38. Barr, A . J., Goodnight, J. H ., Sail, J. P. & H elwig,J. T . (1976) A U ser's Guide to SAS76. SA S (Statistical Analysis System) Insti tute, Inc. , Raleigh, NC.39. Searle, S. R. (1971) L inear M odels, pp. 135-163,John W iley and Sons, I nc., N ew Y ork.40. Corbe , J. L ., Greenhalgh, J. F. D . & Florence, E.( 1959) D istribution of chromi um sesqui oxide andpolyethy leneglycol in the reticulo- rumen of cattle.B ri t. J. Nutr. J3, 337- 345.41. M cConnell, A . A ., Eastwood, M . A . & M itchell,W . D . ( 1974) Physi cal characteri sti cs of vegetabl efoodstuf fs that could inf luence bowel function. J. Sci .Food Agrie. 25, 1457-1464 .42. Kirwan, W . O., Smith, A. N ., M cConnell, A . A .,M itchell, W . D . & Eastwood, M . A . (1974) A ctionof di ff erent bran preparati ons on coloni e f uncti on.Brit. M ed. J. 4, 187-189.43. V an Soest, P. J. ( 1978) Nutri ti onal value of dietaryfibers for humans. GREG Project N o. 1-RO 1-CA -21016-01. Fi nal Report. D epartment of H ealth, Education and Welf are, N ati onal Cancer I nsti tute,Washington, DC.44. Brodribb, A. J. M . & Groves, C. (1978) Effect ofbran parti cle size on stool wei ght. Gut 19, 60-63.45. Cowgill, J. R. & A nderson, W . E. (1932) L axativeef fects of wheat bran and "washed bran" in heal thyman. J. Am. Med. Assoc. 9 8, 1866- 1875.46. Wyman, J. B., Heaton, K . W ., M anning, A . P. &W icks, A . C. B. (1976) The effect on intestinaltransi t and the feces of raw and cooked bran in di ff erent doses. Am. J. C li n. Nutr. 29, 1474- 1479.