Dietary

Devroede,2

bowel

tency time

Bowel

of stools

Several and

of bowel be

comparison

or

meaningful, diarrhea between

should

studies

habits be

suggest

increases

mechanisms

To pation

that water

remain

have

different

recorded addition content

of Am.

unknown.

function1

a diagnosis should be

of Clinical

the

to the

stool.

.1 C/in.

and

including diet

on

reduces

Conflicting Nutr.

frequency,

those

the

long

data

and

are

31: S157-S160,

amount, effects prolongs

difficult

and

consis-

of dietary to

fiber.

short

transit

reconcile,

and

1978.

and it shows a normal g with a large coefficient of based

subjects

constion a and

pa-

).

Journal

study,

of fiber

habits

normal

characteristics,

in any

tients. Therefore, it is surprising that no eva!uation of bowel habits of a healthy random sample of the population eating a standard diet has ever been made. Bowel habits are characterized by several parameters; thus constipation has different meanings for different patients. Most often patients refer to an abnormally how frequency of defecation ( 1 Difficulty of expulsion is second as a complaint, and hard consistency of the stool is another way of characterizing constipation. Some patients complain of all three symptoms. Other characteristics of constipation are a feeling of incomplete evacuation of the rectum and producing abnormally small stools. Each of these symptoms should be discussed with patients who complain of constipation, and they are items to be checked in any study dealing with bowel habits. As mentioned above, no study has been done in a random sample of a healthy population. A random study was done in older people (2), but some of these complained of long-standing constipation, and one had nectal cancer. In another random study with better exclusion criteria (1), subjects had from three stools per day to one every other day; here again, some had chronic constipation, and many were taking laxatives. Available data on normal subjects eating the diet of their choice come from four studies, which have shown that such people have between three stools per day and three per week (1-4). Only one study of stool weight is available, The American

and colonic

M.D.

ABSTRACT

Definition

habits,

Nutrition

31: OCTOBER

stool

weight

is available

range from 35 to 225 of variation for the of each individual (4). No study on other parameters of defeca-

tion.

Dietary

fiber

and bowel

habits

What is the effect of dietary fiber on bowel habits? Interest in this question has increased in the last 10 years with the realization that the treatment of diverticular disease with a low-residue diet was not based on objective data. Indeed, rats develop diverticula when they are fed a low-residue diet. Epidemiological studies also show that there is an association (which does not necessarily mean a causal

relationship)

between

low

intake

of

fiber and incidence of diverticula. A lowresidue diet is also thought to be implicated in the high incidence of bowel cancer in the Western world. Relatively few studies have been carried out on the effects of fiber on bowel habits of healthy subjects, and most of these express results only in terms of weight of stool produced per day without regard to stool frequency and individual stool weight. Dietary supplements of wheat bran and cellulose increase wet weight of stools (5-7), while any increase in dry weight seems mainly limited to

the

ever,

amount

in another

of

bran

study

ingested

(8) suggesting

(5-7).

How-

that

the

‘From the D#{233}partement de Chirurgie, Centre Hospitalien Universitaire, Sherbrooke, Qu#{233}bec, Canada JIH 5N4. 2 Professor of Surgery, Unite of Recherche Gastrointestinale.

1978,

pp.

5157-5160.

Printed

in U.S.A.

S157

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S157/4656086 by East Carolina University user on 10 January 2019

Ghislain

fiber,

DEVROEDE

S 158

Dietary

fiber

and

colonic

function

How does diet affect bowel habits? Two words of caution must be mentioned here. First, all diets have a tremendous placebo effect. In a recent double-blind trial, wheat bran relieved 52% of patients with irritable bowel syndrome while a placebo fared even better with a subjective improvement in 65% of the control group (12). This is similar to a 50% incidence of placebo effect we found in a preliminary survey of a random trial in diverticular disease of the bowel (13). Therefore, any results dealing with symptoms must be viewed with caution. Function could also

C8 .T

possibly be affected. A second problem deals with the ways by which colonic function has been studied. Radioopaque markers permit the study ofcolonic transit time; however, the polyvinyl used for these studies is a marker of the solid phase only. A marked change in stool consistency occurs in some patients with irritable bowel. Stool consistency must also differ in subjects producing 1000 g of stools per day as they do in some countries. This may lead to problems, since radioopaque markers are of no value in diarrhea because of a streaming effect along the bowel (14, 15) as has been demonstrated in studies of bran action (6). Figure 2 represents the results of two studies on the effect of the degree of refinement ofthe diet on bowel transit time (16, 17). The message of both papers is that a refined diet prolongs transit time. However, transit times of

subjects

eating

an

unrefined

or

a mixed

diet are reasonably similar whether transit is measured by radioopaque or carmine markers, and the longest transit times are obtained with radioopaque markers in subjects eating a refined diet. It may be that this greater contrast is partly a reflection of the technique used to measure transit time. Radioopaque markers are probably of great value when comparing healthy subjects and patients on a diet fairly similar in crude fiber content and who produce stools of approximately similar consistency, a characteristic very difficult to objectify. These markers are simply cut from segments of radioopaque Levine tube. The abdomen can be x-rayed to count markers in the different segments of bowel (10) or alternatively the stools may be x-rayed to count how many segments have been passed. A refinement of the technique involves a use of different markers to study mixing (18). When the fiber content is uniform, these markers can be used to distin-

10

> C

5

C

0:5

1.5

2 n stools/day

FIG.

1

.

Average

daily

stool frequency

in healthy

subjects

eating

a diet

containing

14.4

g of crude

fiber.

Downloaded from https://academic.oup.com/ajcn/article-abstract/31/10/S157/4656086 by East Carolina University user on 10 January 2019

cereal manufacturing process alters the properties of wheat bran, it was found that there was no change in wet weight of daily stool output when bran was added to a low-fiber diet. Again dry weight was increased by raw but not cooked bran. There was no effect on stool frequency, and individual stools were heavier with a small dose of raw bran. A fifth study (9) shows that fecal output more than doubled when fiber was added to the diet for over 3 days but that water content did not change. These data are difficult to reconcile. Healthy subjects (10), eating a controlled diet with a l4.4-g crude fiber content, had a normal range of stool frequency between three and I 1 stools per week, a narrower range than normal values obtained without dietary control (Fig. 1). No males and few females had less than five stools per week. On the other hand, with a diet completely depleted in fiber, surprisingly there was no change in stool weight and a decrease in stool frequency only ( I 1). It is evident that subjects on elemental diets do not produce individual stools of 30 g; many studies have been misleading in this regard by reporting only daily outputs when stools are passed infrequently.

DIETARY

FIBER,

EJ

BOWEL

HABITS,

AND

COLONIC

FUNCTION

SI 59

carmine marker radioopaque markers

50 45

35 C

.

‘a-.-

30

.

25

c

20 15 10

[]HH

5 unrefined

FIG.

2

.

Effect

of refinement

of diet

mixed on

bowel

transit

refined

time.

From

Holmgren

and

Mynors

( 17) and

Burkitt

et al.

(16).

guish constipated patients from normal subjects on an objective basis. There is no difference between controls and patients in the right side of the colon, but there is a significant delay in the left and sigmoid colon and rectum (19). Can this technique be used to study the effects of dietary fiber? The normal range of excretion of radioopaque markers is slightly narrower when subjects eat a high-fiber diet than an uncontrolled diet, and all markers are excreted 7 days after ingestion (10). 5everal studies indicate that wheat bran accelerates slow intestinal transit of radioopaque markers. One group of investigators reported that it did not change medium intestinal transit, accelerated initially slower than average intestinal transit, and slowed initial fast intestinal transit, therefore providing an element of regulation (20, 2 1). As a result, the normal range of transit is narrowed and has also been found in patients with diverticular disease given supplements of bran. In another study, however, only large doses of raw bran decreased cohonic transit time. This was of borderhine significance, and there was no change in range (8). In a third study, wheat fiber decreased the mean transit time ofall subjects (7). All studies confirm a previous suggestion that bran regulates bowel habits by correcting eccentric data (22). Once again, the degree to which this effect is nonspecific remains to be seen. There is no correlation (Fig. 3) between transit times of radioopaque markers and stool frequency. This is also true when transit

r

2

0.13

1.5

!

0

2i

I .

Ix

0.5

1

2 3 emptying

time

567 of large bowel

(days)

FIG. 3 . Relationship between stool frequency colonic transit time in healthy subjects eating a diet 14.4 g of crude fiber.

and with

time in each bowel segment is related to stool frequency. If colonic transit is influenced by fiber without change in stool frequency but correlates well with stool weight, this may imply that caliber of the bowel and length of segment emptied at defecation are factors involved. The locations in the large bowel where those changes occur is completely unknown at present. Perfusion of the large bowel coupled with recording of intraluminal pressure shows that the right side of the human colon contracts very regularly when it is quickly filled with fluid (23). The bowel contraction frequency is greater on the heft side of the large bowel than on the right side, therefore creating conditions of storage within the right colon. There are also regional differences in degree of absorption and in

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40

DEVROEDE

S160

eters oflarge entenology,

bowel function in press. 1 1. BOUNOUS, G., AND G. elemental diet on human ogy 66: 210, 1974. 12. S#{216}LTOFT, J., B. KRAG, E. TENSEN AND H. R. WULFF. the effect of wheat bran bowel syndrome. Lancet 13. DEVROEDE, G. In: Fiber Disorders,

I. S. C. An analysis of bowel habit and its significance in the diagnosis of carcinoma of the colon. Am. J. Proctol. 27: 45, 1976. 2. MILNE, J. S., AND J. WILLIAMSON. Bowel habit in olden people. Gerontol. Clin. 14: 56, 1972. 3. CONNELL, A. M., C. HILTON, G. IRVINE, J. E. LENNARD-JONES AND J. J. MISIEWICS. Variation of bowel habit in two population samples. Bnit. Med. J. 2: 1095. 1965. 4. RENDTORFF, R. C., AND M. KASHGARIAN. Stool patterns of healthy adult males. Disease Colon Rectum 10: 222, 1967. 5. EASTWOOD, M. A., J. R. KIRKPATRICK, W. D. MITCHELL, A. BONE AND 1. HAMILTON. Effects of dietary supplements of wheat bran and cellulose on faeces and bowel function. Bnit. Med. J. 4: 392, 1973. 6. FINDLAY, J. M., A. N. SMITH, W. D. MITCHELL, A. J. B. ANDERSON AND M. A. EASTWOOD. Effects of unprocessed bran on colon function in normal subjects and in diverticulan disease. Lancet 1: 146, 1974. 7. CUMMINGS, J. H., M. J. HILL, 0. J. A. JENKINS, J. R. PEARSON AND H. S. WIGGINS. Changes in fecal composition and colonic function due to cereal fiber. Am. J. Clin. Nutr. 29: 1468, 1976. 8. WYMAN, J. B., K. W. HEATON, A. P. MANNING AND A. C. B. WICKS. The effect on intestinal transit and the feces of raw and cooked bran in different doses. Am. J. Clin. Nutr. 29: 1474, 1976. 9. FICHS, H. M., S. DORFMAN AND M. H. FLOCH. The 1.

JONES,

effect

10.

of

dietary

fiber

Alteration

in

Am.

Nutr. H., C.

J. Clin.

MARTELLI, HAN,

edited

New York: 120-123.

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E. KRISdouble-blind trial of on symptoms of irritable 1: 270, 1976. Deficiency and Colonic R. W. Reilly and J. B. Kirsner. Medical Book Co., 1974, pp. GUDMAN-HOYER, A

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transit times in children with gastroenteni16: 458, 1975. FINDLAY, J. M., W. D. MITCHELL, M. A. EAsTwooD, A. J. B. ANDERSON AND A. N. SMITH. Intestinal streaming patterns in cholerrhoeic enteropathy and diverticulan disease. Gut 15: 207, 1974. BURKITr, D. P., A. R. P. WALKER AND N. S. PAINTER. Effect of dietary fiber on stools and transit-times, and its role in the causation of disease. Lancet 2: 1408, 1972. HOLMGREN, G. 0. R., AND J. M. MYNORS. The effect of diet on bowel transit times. South African Med.

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WIGGINS.

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H., G.

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P.

DEVROEDE,

AND transit

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ARHAN

idiopathic

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22.

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R. H., R. B.

HIGGS, BERT.

II.

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1976.

G.

14.

by

Plenum

in normal

obstruction. Gastroenterology in press. R. F., E. W. POMARE AND K. W. HEATON. Effects ofincreased dietary fiber on intestinal transit. Lancet I: 1278, 1973. PAYLER, D. K., E. W. POMARE, K. W. HEATON AND R. F. HARVEY. The effect ofwheat bran on intestinal transit. Gut 16: 209, 1975. WOZASEK, 0., AND F. STEIGMAN. Studies on colon irritation. III. Bulk of feces. J. Digest. Diseases 9: 423, 1942. CHAUVE, A., G. DEVROEDE AND E. BASTIN. IntraluHARVEY,

P. AR-

mmal

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1976.

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histological characteristics in different parts of the large bowel. In patients with severe chronic idiopathic constipation, we found little abnormality in the right side of the bowel. Most ofthe delays were limited to the hindgut (19). It is, therefore, quite possible that the large bowel has different responses to dietary fiber within its different segments. U