The Physiological Effects of Dietary Fiber

21 The Physiological Effects of Dietary Fiber JAMES SCALA

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0015.ch021

Thomas J. Lipton, Inc., Englewood Cliffs, N. J.

In the last century consumption of cereal fiber has decreased more dramatically than either fat or sugar consumption has increased. The9%decline in consumption of cereal fiber compares to a30%increase in fat and a50%increase for sugar. Part of the decline in fiber is probably due to a shift from "crude" sources of carbohydrate such as whole grain cereal, and bread to the "more refined" modern counterparts. Table 1 summarizes the consumption dietary fiber obtained from cereal, potatoes, legumes and fruits and vegetables, as calculated by H. C. Trowell (1) and the author (2). An analysis of the data indicates the change in fiber consumption is largely confined to cereals which have decreased by 75 to 90% fiber from potatoes has decreased by about40%from legumes about20%,while fiber from fruits and vegetables has changed very little. Table 1 Estimates o f D a i l y F i b e r Consumption i n The U.S. i n 1880, 1964, and 1974 F i b e r Source

1880 (1 ) 1964 (1) 1974

Cereals Potatoes Legumes F r u i t s and Vegetables

3.2 1.1 1.0 2.8

0.3 0.5 1.0 3.3

0.8 0.6 0.6 2.0

Total Fiber

8.1

5.1

3.0

(2)

These changes, brought t o the f o r e by B r i t i s h epidemiolog i s t s Drs. Dennis B u r k i t t , Hugh Trowell and the surgeon Dr. N e i l P a i n t e r , r a i s e the question o f what has been s a c r i f i c e d by e l i m i n a t i n g so much c e r e a l f i b e r from our d i e t ( 3 ) . Is f i b e r a f o r gotten n u t r i e n t ? D i e t a r y f i b e r i s defined as p l a n t m a t e r i a l which i s r e s i s t ant t o d i g e s t i o n by the s e c r e t i o n s o f the human g a s t r o i n t e s t i n a l

325 In Physiological Effects of Food Carbohydrates; Jeanes, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.


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CARBOHYDRATES

t r a c t . However, n u t r i t i o n i s t s u s u a l l y speak o f crude f i b e r . "Crude f i b e r " i s the m a t e r i a l l e f t a f t e r treatment with hot a c i d and a l k a l i e , a method o f f i b e r a n a l y s i s developed to t e s t animal feeds f o r undigestable m a t e r i a l . In short, t o p r o t e c t the farmer against poor feed purchases. Consequently, we are l e f t with a value that has l i t t l e , i f any, q u a n t i t a t i v e meaning i n terms of human n u t r i t i o n . Processed g r a i n s c o n t a i n v a r i o u s amounts o f c e l l u l o s e , h e m i c e l l u l o s e , p e c t i n and l i n g i n s , a l l of which are defined as f i b e r ; t h e i r q u a n t i t i e s v a r y with v a r i e t y , p r o c e s s i n g , climate and other f a c t o r s . Consequently, d i e t a r y f i b e r , the und i g e s t i b l e p l a n t carbohydrates, i s from 2 t o 6 times the crude f i b e r content o f food (k). This impreciseness i s a challenge t o food t e c h n o l o g i s t s , and speaks f o r the need t o f i n d a method which w i l l a c c u r a t e l y i d e n t i f y the amount o f " d i e t a r y f i b e r " i n food. I w i l l review the major p h y s i o l o g i c a l e f f e c t s of d i e t a r y fiber. T r a n s i t Time F i b e r increases s t o o l frequency and decreases t r a n s i t time of m a t e r i a l s p a s s i n g through the l a r g e i n t e s t i n e . These two e f f e c t s are i n d i r e c t r e s u l t s of the water b i n d i n g a b i l i t y o f f i b e r and have been demonstrated by comparing s t o o l t r a n s i t times to those on a r e f i n e d , low f i b e r d i e t ; f o r example, an E n g l i s h or U. S. d i e t . Table 2 summarizes data taken from studies by Burk i t t i n which t r a n s i t time was evaluated as a f u n c t i o n o f diet.(5) These comparisons o f p o p u l a t i o n groups have been c l i n i c a l l y e v a l uated and demonstrate that a d i e t h i g h i n f i b e r increases both s t o o l weight and frequency. The increased weight i s due t o the water b i n d i n g c a p a c i t y o f f i b e r which c a r r i e s h t o 6 times i t s weight through the l a r g e i n t e s t i n e . This water i s "bound" i n the s o l i d phase (7) and; consequently, a h i g h f i b e r d i e t w i l l r e s u l t i n l a r g e r and more frequent e l i m i n a t i o n - or i n l a y termsregularity (7). Table 2 T r a n s i t Time as a F u n c t i o n o f D i e t Subject

Diet

T r a n s i t Time

Ugandan V i l l a g e r s and Students

Unrefined

33

35 hours

E n g l i s h Vegetarians, South A f r i c a n P u p i l s and Indian Nurses

Mixed

h2

hours

E n g l i s h Students and Navy Personnel

Refined

69 hours

In Physiological Effects of Food Carbohydrates; Jeanes, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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T r a n s i t times reported i n Table 2, were evaluated by the method o f Hinton (6) i n which radiopaque p e l l e t s ( r i c e g r a i n i n s i z e ) are f e d to volunteers and are observed by X-ray o f the passed, c o l l e c t e d , s t o o l s . Hinton defines t r a n s i t time as the time r e q u i r e d t o pass 80& o f the p e l l e t s .


D i v e r t i c u l a r Disease D i v e r t i c u l a r disease a f f e c t s about 20& of a d u l t s i n the United States - and with increased l o n g e v i t y , i t s numbers i n crease every year. Estimates by B u r k i t t and Trowell i n d i c a t e that i t i s growing at a r a t e of l6& per year ( l ) . T h i s r a t e can be questioned because i t i s not age and l o n g e v i t y compensated. Table 3 summarizes h e a l t h s t a t i s t i c s i n the U. S. which demons t r a t e the age r e l a t i o n s h i p o f d i v e r t i c u l a r disease ( 8 ) . Other e p i d e m i o l o g i c a l surveys have shown c o r r e l a t i o n s of d i v e r t i c u l o s i s with a p p e n d i c i t i s , (9) v a r i c o s e v e i n s , (10) and hemorrhoids. Table 3 D i v e r t i c u l a r Disease as a Function of

Age

Incidence

Age Under 35

^5 - 5^ 60 - 70 over

70

10& 25&

D i v e r t i c u l o s i s i s c h a r a c t e r i z e d by small defects which develop as bulges i n the w a l l of the colon; they are s i m i l a r i n appearance to the bubble which appears at a weak p o i n t on an i n f l a t e d rubber tube. C l i n i c a l l y , they are s a c c u l a r outpouchings o f the mucosa and submocosa which extrude through defects i n the muscularis. As these evaginations f i l l with i n t e s t i n a l contents or gas, they become i n f e c t e d and i n extreme cases, gangrenous. In a l l cases, they are p a i n f u l and u s u a l l y r e q u i r e surgery, i n which the diseased p o r t i o n of the i n t e s t i n e i s removed - a process which o f t e n i n c l u d e s a temporary colestomy. In 1967 Dr. N e i l P a i n t e r found that a high f i b e r d i e t would r e l i e v e the symptoms of d i v e r t i c u l o s i s and could, i n some cases, obviate the need f o r surgery ( l l ) . Of the 70 cases he t r e a t e d with a high f i b e r d i e t , 62 could be spared from surgery. Data from Dr. P a i n t e r s o r i g i n a l 62 p a t i e n t s ( t a b l e k) show that previous t o the high f i b e r regimen the d i v e r t i c u l a r p a t i e n t s had i r r e g u l a r , infrequent, hard s t o o l s , and the simple procedure o f t a k i n g about 15 grams of bran d a i l y i n three servings of two tablespoons each, produced r e g u l a r i t y and eliminated the symptoms. The means by which f i b e r r e l i e v e s , the symptoms of d i v e r t i c u l o s i s has been more c l e a r l y shown by Eastwood who s t u d i e d d i v e r t i c u l a r p a t i e n t s on a high f i b e r d i e t and compared them t o a T


328

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group o f normal h e a l t h y volunteers

EFFECTS

OF

FOOD

CARBOHYDRATES

(7).

Table k Bowel Habits of 62 P a t i e n t s Before and A f t e r Taking B r a n ( l 2 )


Bowel Habit (Frequency of E l i m i n a t i o n s ) Irregular Every 3 days Every 2 days Once d a i l y Twice d a i l y Three times d a i l y Frequent s t o o l s

Before Bran

13 7 8 28 3 none

3

After Bran

31 25 6 none

The d i v e r t i c u l a r p a t i e n t s on Eastwood's high f i b e r d i e t confirmed P a i n t e r ' s f i n d i n g s and e x h i b i t e d : l ) more normal waste t r a n s i t times when put on a bran d i e t v e r i f y i n g P a i n t e r s observ a t i o n s , 2) t h e i r i n t r a c o l o n i c pressure was reduced to more normal values s i m i l a r t o the observations of Hodgson, (13) and 3) the r a t i o of bound water to l i q u i d water i n the feces becomes more s i m i l a r to the normal p a t i e n t s . These observations suggest that f i b e r i s e f f i c a c i o u s by t r a n s p o r t i n g a l a r g e r volume o f water s t o o l s i n t o the l a r g e i n t e s t i n e . These s o f t e r , b u l k i e r s t o o l s reduce the i n t r a c o l o n i c pressure p r e v e n t i n g d i s t e n t i o n o f the d i v e r t i c u l a . However, i t i s more important t h a t f i b e r probably prevents the development o f high i n t r a c o l o n i c pressures which l e a d t o the formation of d i v e r t i c u l a . In a d d i t i o n , a high f i b e r d i e t may induce a much stronger i n t e s t i n a l musculature c o n t a i n i n g fewer weak spots which are p o t e n t i a l s i t e s o f d i v e r t i c u l a . This prev e n t i v e p o t e n t i a l f o r f i b e r could be t e s t e d by animal s t u d i e s . 1

Cardiovascular Disease The low incidence of ischaemic heart disease and low serum c h o l e s t e r o l among p o p u l a t i o n groups on an u n r e f i n e d , high residue d i e t has been a t t r i b u t e d , i n p a r t , to the hypocholesterolemic e f f e c t o f n o n d i g e s t i b l e carbohydrate ( l U ) . The d i e t o f these people i s o f t e n , but not always, low i n f a t ; long term studies with South A f r i c a n White and Bantu p r i s o n e r s on c o n t r o l l e d d i e t s has confirmed the hypocholesterolemic e f f e c t o f f i b e r (15). Comp a r a t i v e s t u d i e s of p o p u l a t i o n groups are summarized on Table 5·


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Dietary Fiber Table 5 Serum C h o l e s t e r o l i n Population Groups Where D i e t D i f f e r s i n F i b e r Content (ik) (15) (l6)


Group

Blood Cholesterol

Diet

New Guinea (Male) New Guinea (Female) New Guinea (Male) New Guinea (Female) Non Vegetarians Lacto Vegetarians Vegan Vegetarians T r a p p i s t Monks Benedictine Monks

Unrefined Native Unrefined Native Western Refined Western Refined Western Vegetarians (Dairy) S t r i c t Vegetarian Lacto Vegetarian Mixed

lOÇjmg^ 13*+ 183 187 291 256 206 l80 225

Other s t u d i e s have been performed d i r e c t l y to evaluate the hypocholesterolemic o f d i e t a r y f i b e r . In general, these s t u d i e s i n d i c a t e that a d d i t i o n o f f i b e r t o the d i e t reduces serum c h o l e s t e r o l by preventing absorption o f d i e t a r y c h o l e s t e r o l and by i n c r e a s i n g the e l i m i n a t i o n o f b i l e a c i d s ; thereby, the removal o f h e p a t i c synthesized c h o l e s t e r o l . These f i n d i n g s have been confirmed by extensive animal s t u d i e s (33), (3J0. These s t u d i e s are summarized i n Table 6. In general, these s t u d i e s have been done over short periods and have u t i l i z e d f i b e r as r e f i n e d c e l l u l o s e , or from n a t u r a l sources. Table 6 The E f f e c t o f D i e t a r y F i b e r on Serum C h o l e s t e r o l on Man Control Diet

Subjects Young G i r l s

(19)

(Cellulose)

226 Male Volunteers (20)

(21)

170 (Oats)

251 Male Volunteers

Experimental Diet

206

223 (Bengal Gram) l60

Although the hypocholesterolemic aspects o f f i b e r has not been q u a n t i f i e d , these s t u d i e s demonstrate i t s e f f e c t i v e n e s s as i n f e r r e d from serum c h o l e s t e r o l . F i b e r helps i n e l i m i n a t i n g both d i e t a r y and h e p a t i c c h o l e s t e r o l thereby reducing, t o some extent, one major r i s k f a c t o r o f c a r d i o v a s c u l a r disease - serum c h o l e s terol.


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Colonic

EFFECTS

O F FOOD

CARBOHYDRATES

Cancer

Since f i b e r i n c r e a s e s the speed o f m a t e r i a l through the gut and the volume which i s passed, i t would be expected t o reduce the exposure time o f the gut t i s s u e s t o any non d i g e s t i b l e com ponent. Therefore, duductive reasoning leads us t o expect i t t o reduce the likelihood o f c o l o n i c t o x i c i t y d e r i v e d from any i n gested o r p h y s i o l o g i c a l l y produced t o x i c agent. Toxic agents o f greatest concern i n the gut are carcinogens. Although s t u d i e s t o r e l a t e f i b e r , i n g e n e r a l , t o the reduc t i o n o f cancer have been u n s u c c e s s f u l , the recent e p i d e m i o l o g i c a l e v a l u a t i o n o f Drs. I r v i n g and Drasar have shown a s i g n i f i c a n t a l b i e t small, negative c o r r e l a t i o n with c o l o n i c cancer and c e r e a l consumption ( 2 2 ) . Although the c o r r e l a t i o n s account f o r a small p o r t i o n o f c o l o n i c cancer, i n t u i t i o n and epidemiology are i n such obvious agreement that the t r e n d i s s i g n i f i c a n t and a milestone i n epidemiology. These c o r r e l a t i o n s are summarized i n Table 7 · Table 7 C o r e l a t i o n o f Cancer o f the Colon With Consumption of Various F i b e r Containing Foods (22) Correlation Coefficient

Source o f F i b e r Cereals Potatoes and Starches Pulses Nuts and Seeds Vegetables Fruit

-0.30 -0.07 +0.07 +0.05 +0.22

Statistical Significance 0.10^P^0.05 N.S. N.S. N.S. N.S.

C o l o n i c cancer i s second only t o lung cancer as a k i l l e r among cancers. I t occurs l e a s t f r e q u e n t l y i n populations with a h i g h residue u n r e f i n e d d i e t such as i n C e n t r a l A f r i c a ( 2 3 ) . This has been observed by e p i d e m i o l o g i s t s who have evaluated b l a c k s l i v i n g i n A f r i c a against b l a c k s i n the U. S. o r Japanese i n Japan t o those i n the U. S. These data presented i n Table 8 are taken from evaluations by Dr. Robert D o l l at Oxford, and have been con firmed by other e p i d e m i o l o g i c a l surveys (2h). Colon-Cancer

Table 8 Incidence i n Males by Race and Country

Country U. S. ( C a l i f o r n i a ) U. S. (Hawaii) U. S. (Hawaii) Rhodesia Japan (Rural) South A f r i c a Nigeria

Race Black Caucasian Japanese Black Japanese Black Black

Incidence 69.8 68.0 66 Λ 18.2 11.8 10.8 5·8


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Dietary Fiber


Colonic cancer i s highest i n c o u n t r i e s which e x h i b i t a high incidence o f c a r d i o v a s c u l a r disease and the two are h i g h l y c o r r e l a t e d (25). Therefore, since c h o l e s t e r o l i s the most widely accepted r i s k f a c t o r i n c a r d i o v a s c u l a r disease, i t i s a common b a s i s on which to compare the two d i s e a s e s . Rose observed 5 groups o f people with high r i s k f o r c a r d i o v a s c u l a r disease by t h e i r h i g h serum c h o l e s t e r o l ; then searched f o r the d i f f e r e n c e s among those who had c o l o n i c cancer (26). As Table 9 i n d i c a t e s , the c o l o n i c cancer p a t i e n t s e x h i b i t e d lower than expected serum c h o l e s t e r o l l e v e l s f o r a group at r i s k , as compared to other cancers o f the alimentary system. Table 9 Serum C h o l e s t e r o l D e v i a t i o n s i n Men Who Died o f Alimentary Carcinoma* Site

Mean D e v i a t i o n (Standard U n i t s ) +0.20 ( W h i t e h a l l Study) -0.13 (Whitehall Study) -O.512 (General E l e c t r i c Study)

A l l cancer except colon Colon Colon

^-Adapted from Rose

(26).

Dr. E r i k B j e l k e had conducted a r e t r o s p e c t i v e and prospec t i v e study on the i n t e r r e l a t i o n s h i p between d i e t and c h o l e s t e r o l (27). The group e x h i b i t e d an elevated c h o l e s t e r o l ; however, those with lower c h o l e s t e r o l e x h i b i t e d the higher incidences o f c o l o n i c cancer. As Table 10 i n d i c a t e s , t h i s r e l a t i o n s h i p t e s t e d out c o n s i s t e n t l y over the f i v e year p e r i o d during which the group was followed confirming the f i n d i n g s o f Rose and adding the v a l uable dimension o f p r o s p e c t i v e epidemiology. Table 10 R e l a t i v e Risk f o r C o l o n i c Cancer As a Function o f Serum C h o l e s t e r o l *

Mean C h o l e s t e r o l

Retrospective Relative Risk

291 287 271

Prospective Relative Risk

1.0 1Λ 2.1

^Adapted

from B j e l k e

1.0 2.3 2.0 (27).



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CARBOHYDRATES

Other forms o f suspected d i e t r e l a t e d cancer d i d not e x h i b i t t h i s same p a t t e r n - adding more confirmation t o the f i n d i n g ; t h a t i s , c o l o n i c cancer among high serum c h o l e s t e r o l c a r d i o v a s c u l a r disease r i s k p a t i e n t s i s i n v e r s e with serum c h o l e s t e r o l . These s t u d i e s r a i s e an obvious question, "What do these people pass i n t o t h e i r l a r g e i n t e s t i n e s which w i l l reduce serum c h o l e s t e r o l below i t s expected value?" One component i s obviousb i l e a c i d s , d i e t a r y s t e r o l s and f a t . Since 19^0, i t has been known t h a t deoxydiolate, a b i l e a c i d by-product i s a weak carcinogen (28). High f i b e r u n r e f i n e d d i e t s produce a spectrum o f b i l e s a l t s which are s u b s t a n t i a l l y d i f f e r ent from those observed on a r e f i n e d low residue d i e t . This i s i l l u s t r a t e d by comparing the b i l e a c i d by-products i n r u r a l A f r i c a n s t o Europeans, as done by Dr. James F a l a i y e o f N i g e r i a (29). His data (Table 11) shows t h a t there i s more deoxycholate i n the feces o f people on low residue than on high residue d i e t s . Table 11 B i l e S a l t Ratios and D i e t * Population Group

Diet

N i g e r i a n Adults E n g l i s h Adults

Unrefined Refined

Cholate 1.5 l.h

Data adapted from F a l a i y e

ChenοDeoxycholate

DeoxyCholate

1.0 1.0

O.k 0.9

(29).

These b i l e a c i d by-products are produced by the anaerobic m i c r o f l o r a . People on a r e f i n e d d i e t have a much greater popu l a t i o n o f anaerobes i n t h e i r l a r g e i n t e s t i n e (29). This i s apparent by c o n t r a s t i n g the r a t i o o f i n t e s t i n a l aerobes of Black Ugandins to Blacks i n the U. S. (30), (31) Along with the b i l e a c i d hypothesis, components of the food i t s e l f should be considered. Nitrogen metabolites ranging from ammonia, n i t r o s o compounds and other amines have been i m p l i c a t e d (32). T h e i r production s i m i l a r l y depends upon transformations by the i n t e s t i n a l f l o r a and the l o g i c o f development f o l l o w s a p a t t e r n s i m i l a r to the one considered f o r b i l e a c i d s . A v i r u s hypothesis i s s i m i l a r except t h a t t r a n s i t time and volume are the cogent f a c t o r s . In each hypothesis, f i b e r emerges as a preven t i v e agent. Conclusions The r o l e o f f i b e r i n the d i e t i s emerging as a preventive agent f o r problems o f the alimentary and v a s c u l a r system. This c o n c l u s i o n i s supported by epidemiology, d i r e c t experimentation, and i n f e r e n c e s from d i e t a r y p a t t e r n s i n ethnic and socio-economic


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333


groups. More research i s r e q u i r e d by food s c i e n t i s t s on f i b e r as a food component and by b i o m e d i c a l s c i e n t i s t s on the l o n g term e f f e c t s o f f i b e r i n the d i e t . I n view o f t h e complexity o f t h e d i e t a r y relevance such s t u d i e s should be l o n g term and cover s e v e r a l age groups. Much work remains t o be done on animals; e s p e c i a l l y f e e d i n g s t u d i e s on primates.


334

PHYSIOLOGICAL


Literature

EFFECTS

O F FOOD

CARBOHYDRATES

Cited

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The Physiological Effects of Dietary Fiber

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