Ted Altar
         "Things sweet to taste prove in digestion sour"
          Shakespeare (from "The Winter's Tale, III:2)
Topics briefly covered:
     I     Introduction
     II    Importance Of Fibre
     III   Kinds Of Fibre:
     IV    What Fibre Does:
     V     How Does Cooking Affect Fibre?
     VI    How The Gastrointestinal Tract (Gi) Is Affect By Fibre
     VII   Detoxification
     VIII  Potential Problems With Too Much Fibre
     IX    Fibre Intake And Vegetarians
     X     Dietary Fibre Of Some Common Foods
     XI    References:


Some recent queries about fibre have arose.  To help sort things
out a bit, I hope you will find the following information to be


An adequate intake of fibre has great importance for health as
indicated by its demonstrated physiologic effects.  Among these
   - the hypoglycemic effect of soluble fibre (reduces high blood
           sugar levels)
   - the hypolipidemic effect of soluble fibre (reduces high
       blood fat levels, i.e., those lipoproteins like LDL
       cholesterol, etc.)
   - the lowering of serum cholesterol levels.  Such a lowering,
       as we know, presently appears to have a significant
       benefit in the prevention of atherosclerosis
   - slowing the absorption of carbohydrate can be very useful to
       the diabetic in regulating blood sugar levels.
   - anti-toxic effects.  Most international epidemiological
       studies show an inverse relationship between colon cancer
       mortality and fibre content of diet.  While these studies
       often fail to disentangle the known effects of fat and
       energy intake on colorectal cancer, some studies have
       still found a inverse relationship after these factors
       have been statistically adjusted for.   Besides the anti-
       toxic effects discussed below, the reduced intestinal
       transit time is also thought to be a key factor.
   - apparent reduction or control of gastrointestinal disorders
       that include diverticular disease, gallstones, irritable-
       bowel syndrome, inflammatory bowel disease and
   - the satiety effect that can help *some* individuals better
       maintain their ideal body weight (also helps a little with
       reducing certain dietary utilization of some sugars and
It is important to recognize that various kinds of fibre perform
different function and therefore a variety of fibre containing
foods should be contained in one's diet.  Eating oat bran alone
is simply a bad way to get fibre.  Indeed, there is some folly to
the careless practice of adding large amounts of a single source
of purified fibre to the diet.  Varied whole plant foods is still
the best course to take.
Dietary fibre is derived from solely from plant cells, mostly
from the plant cell wall.  It is NOT to be found in any animal
product. Dietary fiber is not a single entity but in fact
consists of many substances, as we shall see, and each has
different properties. Important properties of fibre include
     Hydrophilic - literally, "water-guarding"  which means that
          it readily expands and holds onto water as it dissolves
          turning things into a stable soup or thin, viscous
          gel.  Thus they are used as "stablizers" which means
          that it helps to keep ingredients dissolved and at an
          uniform consistence or texture.
     Absorbability.  Fibre differ in their absorption of
          fluids, like that of digestive biles.
     Fermentability.  Fiber varies in how well it can feeds the
          good bacteria in the human gut.
     Mechanical properties.  Increasing particle size helps to
          increase the absorptivity of fiber to absorb.  The more
          curly shaped a fiber particle becomes, the better for
     Gel forming - All gums are soluble in water and produce
          viscous solution, but only a few gums have the ability
          to form rigid textures that do not flow.  As we shall
          see, gellation helps to slightly reduce the absorption
          of fats and sugars
     Fecal bulk producing - Considered a desirable thing so as to
          decrease intestinal transit time.  Highly fermentable
          fibers produce less fecal bulk.
Now that we have briefly describe some of the properties of
fiber, it now time to bite the bullet and learn about the
different types of fibre.  Below are the major dietary "fibre"
substances to be found.  :
     cellulose - consists of a polymer chain of glucose units.
          This is the only fibre component with a truly fibrous
          structure.  A major component in vegetable and legume
          fibres.  Also found in most fruits.  Fermentability:
          low in cereals and moderate in legumes
     hemicellulose - these sugar containing substances are more
          accessible to bacterial enzymes than is cellulose.  A
          major constituent of cereal fibre.  Wheat bran in
          particular has a large amount of hemicellulose.
          Fermentability: moderate-high, very low in raw corn
     gums - these are hydrocolloids secreted by the plant at
          injury sites.  They are composed of various sugars and
          sugar derivatives.  They also can be highly soluble and
          gel forming. E.g., guar gum.  Fermentability: high
     pectin - these polysaccharides are water soluble and gel
          forming . Found in fruits and to a lesser extent in
          vegetables. Fermentability: high
     mucilages & algal polysaccharides - agar and carrageenan are
          examples of algal polysaccharides.  Agar is a seaweed
          extract. Because of their "hydrophylic" (literally,
          water-guarding) properties they are used as stablizers.
          "Guar", which is a mucilage, is in fact secreted by
          plant cells to protect the seed endosperm from
          desiccation.  Fermentability: high
     lignin - this is the primary noncarbohydrate component of
          fibre and is very inert.  Highest in mature root
          vegetables like carrots or fruits with edible seeds
          like strawberries.
Sorry about introducing so many new terms, but it is important to
understand that there are DIFFERENT kinds of fibres and they do
not all play the same physiologic and nutritional role.  Just as
not all fats are equal (or even saturated fats for that matter),
so too with fibre.  And just as we need to eat a variety of
vegetables, so too with dietary fiber.
If you are now a little confuse about fibre, you are not alone.
In fact, nutritionists themselves disagree as to which
substances should be consider dietary "fiber" and there is no
"universally accepted definition for this food component" (Hunt &
Goff, 1990).  At least not quite yet.  Some nutritionists did not
consider lignin to be fiber, hence the differences one might find
between estimates of total fiber in common foods (e.g., the
Southgate method includes lignin, the Englyst method does not)
Generally speaking, fibre has been considered is foodstuff that
resists digestion, at least until they enter the large intestine
unchanged.  But which "foods" and what kind of changes?  Maybe
the most widely accepted definition was proposed by Trowell et al
    "plant polysaccharides and lignin which are resistant to
    hydrolysis by the digestive enzymes of man"
One problem even with this definition is that it doesn't include
all the indigestible residues from food that may reach the colon.
Some potentially digestible starches may reach the colon in an
unaltered state.  This can occur in varying amounts.  Yet, no one
considers such starches to be fiber (because they are
"potentially" digestible before reaching the colon), yet they fit
the above definition as it stands.
Another problem with the above definition is that it is
predicated on the idea of "undigestibility" as a criterion, but
some so-called "undigestible" foods (e.g., nonstarch
polysaccharides) can undergo fermentation by colonic bacteria
thereby producing short-chain fatty acids that can be used for
energy by the host.  This are considered to be fiber, yet they
are "digestible" and so we must now note that no longer can the
potential energy in fibre be considered totally unavailable to
the human body.  An interesting development.
In sum, most researchers believe that materials such as resistant
starch and man-made ingredients should not be considered
components of dietary fibre -- Styrofoam packing "peanuts" are
not to be considered fibre even if they do provide bulk  ;-)
Joking aside, it is should be obviously that one must eat a
variety of *plant* foods in order to get each of these important
fiber substances well represented in your diet.


            |-   protein
    plant   |    lipids (fats)
    cell ---|    inorganic constituents
    wall    |    lignin                 -|
            |    cellulose               |
            |    hemicellulose           |--- dietary
            |-   pectins                 |    fibre
                 gums                    |
                 mucilages               |
                 algal polysaccharides  -|
cellulose         -|             -|              -|
insoluble non-     |-insoluable   |               |
  cellulosic       |   fibre      |-Englyst       |
  polysaccharides -|              |  fibre        |-Southgate
                                  | (non-starch   |  fibre
soluble non-       -|             |  poly-        |  (unavailable
  cellulosic        |-soluble     |  saccharides) | carbohydrate)
  polysaccharides  -|   fibre    -|               |
lignin                                           -|
Fibre has an effect throughout the gastrointestinal tact,
beginning in the mouth.  Insoluble fibre components (lignin,
cellulose and most of the hemicellulose) necessitate greater
chewing which in turn stimulates saliva secretion, together which
serves as a tooth cleaner. Eat some fruit if you forgot your
toothbrush :-)
Some of the more important gastrointestinal responses to the
ingestion of fibre include:
    - increased fecal bulk
    - decreased intraluminal pressure
    - greater frequency of defecation
    - reduced intestinal transit time
    - delayed gastric emptying
    - increased postprandial satiety
    - reduced glucose absorption
    - changes in pancreatic and intestinal enzyme activity
    - increased bile-acid excretion
    - possible alteration in mineral balances
Different fibre components will, of course, produce these effects
in different degrees.


While cooking and kitchen processing is not going to decrease or
increase the total amount of major fibres, heat from cooking can
make certain "indigestible starches" more digestible.
Conversely, what is called "Maillard products can occur (enzyme-
resistant linkages between amino acids of proteins and the
carboxyl groups of reducing sugars), particularly from baking and
frying.  Of course, there is debate as to whether or not include
such Maillard compounds as components of dietary fibre.  Most
researchers prefer not to consider as components of fibre either
the resistant starch or Maillard compounds.
It is also the case that the size of the particles and/or degree
of processing of the foods providing fibre appear to influence
the GI response to ingested fibre.  For example, coarsely ground
bran has a higher hydration capacity than that which is finely
ground.  Hence, coarsely ground bran increases fecal volume by
its water-holding capacity, and it also speeds up fecal passage
time through the colon. With respect to emptying food from the
stomach, these larger particles slow it down rather than speed it


Important characteristics of dietary fibre with respect to its
physiologic role in the GI includes:
                hydration capacity
                absorptive attraction for organic molecules
                cation exchange capacity


The upper GI is affected more by the gellation effect of pectins
and hydrocolloids (i.e. the gums, mucilages and algal
polysaccharides) than by the hydration effects of cellulose and
hemicellulose, irrespective of particle size.
Hydrocolloids and pectin reduce the rate of glucose absorption,
and also decrease the rate of absorption and/or availability of
fats and proteins.  The reduction in "apparent protein
digestibility" is likely nutritionally insignificant.  While some
hydrocollids are natural components in beans and certain cereals
(e.g., oats and barley), most enter the food supply as additives
used in processed food.
This decrease on lipid absorption by fibre is not well
understood. Some general effects of fibre on nutrient absorption
that have been proposed that could in part account for this
decreased absorption (e.g.., blunting of villi in the small
intestine, decreased secretion of GI and pancreatic hormones,
direct reduction of pancreatic enzyme activity, decreased
diffusion rate in the proximal intestine due to an increased
thickness of the unstirred water layer, and decreased solute
movement within the lumen of the intestine).  More specific
mechanisms include the lowering of bile acid concentration by
their absorption into the fibre.
Pectin and guar gum (12-30 g/daily) have been shown to lower
serum cholesterol by 6-15% in normal volunteers.  A number of
mechanism have been proposed for the blood cholesterol lowering
effects of fibre. For instance, when fibre absorbs bile acids it
thereby removes some bile from circulation.  A decrease in bile
acids returned to the liver would cause diversion of some
cholesterol from lipoprotein synthesis to the synthesis of bile
acids, thereby lowering serum cholesterol. Another proposed
mechanism involves the fibre stimulated shift of bile acid pools
toward chenodexoycholic acid -- which inhibits cholesterol
synthesis.  It is thought that the chenodeoxycholate alerts the
liver through inhibition of a key enzyme that no more cholesterol
is needed for bile acid synthesis.  Still, neither of these
proposed mechanisms fully explains the degree to which fibre can
lower serum cholesterol.
Another effect of fibre is its influence on cation aDsorption,
particularly calcium, zinc and iron.  Not only do the cation
bridges formed by fibre serve as a mechanism for the adsorption
of bile acid and fats, but also of minerals.  This can ultimately
help or hinder mineral absorption, depending upon the
fermentability (or its accessibility to bacterial enzymes) of the
fibre when it enters the lower GI.


It is here where most of the signification action of dietary
fibre occurs.  Fermentation of food by colonic anaerobes make
available to the body much of the energy of undigested foods
reaching the cecum. This has indeed been an overlooked source of
energy.  For instance, as much as 10% to 15% of the carbohydrates
we eat in the West may be fermented in the colon.  In general,
from 40-95% of dietary fibre is fermented by intestinal flora.
Certain fibres, like the plant gums (and any starch that has
passed undigested into the cecum), are rapidly fermented by
various anaerobic bacteria residing in the colon.  The main
metabolites produced by this rapidly fermentable fibre are some
short-chain fatty acids (acetic, butyric & propionic acids).  By-
products of this fermentation are hydrogen, carbon dioxide and
methane.  Keep matches away!  These gases are excreted as flatus
or are expired by the lungs.
These fatty acids produced by fermentation are rapidly absorbed
or are used by the epithelial cells of the colon for energy.  The
propionic acid produced from fibre may also contribute to the
cholesterol lowering effect of certain fibres by acting to
inhibit a rate-limiting enzyme (HGG CoA reductase) in the
synthesis of cholesterol in the liver.
The more slowly fermentable or non-fermentable fibres than the
gums are particularly helpful for overcoming constipation by
increasing fecal bulk (1) water absorption and/or (2) promotion
of microbe proliferation.  Slowly fermentable fibres, like cereal
fibres, are particularly valuable in causing microbial
proliferation.  Bacterial cells form part of the fecal mass and
provide moisture.  The volatile fatty acids produced by the
bacteria acidify the colonic content, act on the musosa and,
following absorption, modify the lipid metabolism. Due to these
two factors, it has been shown that for every extra gram of
cereal fibre stool weight gains an extra 2 to 9 grams!
Wheat bran, for instance, can absorb 3 times its weight in water
thereby producing a much softer, bulkier stool.  The large wheat
bran particles take a curly shape on fermentation, constituting
microenvironments in the distal colon, and providing a physical
resistance against the removal of interstitial water and
dispersed gases, thus counterbalancing the absorptive capacity of
the colon. The resulting decrease in fecal density prevents
impaction and constipation.  The threshold volume is rapidly
attained in the rectum triggering defecation, thus limiting the
opportunity for reabsorption and hardening of the intestinal
It should be noted that reducing particle size eliminates this
effect since small particles retain non-solid components less
effectively. Coarse bran will reduce colon segmenting activity
and intraluminal pressure, normalizes slow transit time (40-150
hours) to about 20 hours, increase fecal weight (4 times more
than fine bran and 7 times more than oat bran).
Interestingly, rice bran has been found to be even more effective
in increasing fecal bulk, frequency of defecation and reduced
intestinal transit time.  Now only are these responses are
particularly important in the prevention of constipation, but
they may be advantageous in the management of irritable colon and
diverticular disease).


Microbial proliferation and excretion is not only important for
increasing fecal volume but is thought to play an important role
as a "DETOXIFICATION MECHANISM".  Do not confuse this term with
what the colon irrigation quacks call "detoxification".  They are
not the same thing.
It works as follows.  Increased microbial cell synthesis would
scavenge degradable nitrogenous substances and thereby sequester
those substances into the microbes themselves, which in turn are
eventually excreted.
The downside to this function is that excessive microbial
proliferation may decrease mineral absorption.  What is thought
to happen is that certain essential elements may become bound in
the microbial cells themselves, to then be excreted rather than
absorbed. In contrast, the more rapidly fermentable fibre
components release their calcium, zinc and iron for absorption by
the colon as fermentation occurs.
Fibre from fruit and vegetables is less effective in increasing
fecal bulk since much of their fibre consists of rapidly
fermentable pectin and the less microbial promoting cellulose.
Hence, for every 1 gram extra of vegetable fibre consumed, only
about a 1.9 gram increase in fecal weight occurs.  In contrast to
cereal fibre, fruit and vegetable fibre which contain
considerable amounts of pectin, can delay gastric emptying and
reduce glucose absorption because of its gellation quality.
It would seem that both fast and slow fermentable fibres should
be consumed.  Again, it is not simply the amount of fibre that
should be important, but also that fibre from VARIOUS sources be
ingested so that a varied selection of fibre components are part
of one's diet.
A comparison of the levels of mutagens in the faeces of 12
omnivores, 6 vegetarians and 6 vegans showed even with this small
sample significant lower levels in the vegans and vegetarians
volunteers showed (to pick up a statistically significant effect
in a small sample requires that the size of the effect size be
large).  Another study with volunteers on 20-day experimental
diets showed that vegan diets produced the lowest concentration
of bile acids, and of course cholesterol, in their faeces.
Apparently a high concentration of bile acids or cholesterol in
faeces is associated with risk of colorectal cancer.


There are few reports of adverse effects on the gastrointestinal
tract directly related to fibre.  Excessive intakes of
particulate fibres (e.g., cereal fibres), for instance, have been
reported to produce intestinal obstruction in susceptible
individuals.  In general, more finely ground fibre (even from
wheat bran) may cause difficult or uncomfortable defecation.  The
mean particle size of fibre in ready- to-eat breakfast cereals
varies from 350um to above 1mm.  The number of particles less
than 150um appears to be negligible.
Excessive fibre consumption may cause a transient fluid imbalance
when the fibre consumed absorbs a lot of water.
An excessive intake of nonfermentible fibre could make for a
negative mineral balance, particularly among infants, children,
adolescents, and pregnant women whose mineral needs are of course
relatively greater than for adult men or nonpregnant woman.  If
the intake of calcium, zinc and iron is marginal, then excessive
fibre could exacerbate the already low intake of these minerals.
The nutrition recommendations from the 1990 Canadian scientific
review committee concluded that "evidence of mineral binding is
unequivocal but it is doubtful whether such effects are of any
nutritional importance in the context of an adequate diet".
     "If the ordinary man or woman were confronted for the first
     time with the offensive contents of a constipated large
     bowel, and were told that the body he or she thinks so much
     about... was the casket of such a jewel the shock and
     disgust might almost prove fatal"  ;-)   :-)
          [from F. A. Hornibrook, "The Culture of the Abdomen",


We've seen that a varied selection of fibre should be ingested,
now the question is how much?
The recommendation for the general population has ranged from 20
to 40 grams/day, and may up to 50 gram/day for
hypercholesterolemic individuals.  The National Health and
Nutrition Examination Survey (1976-1980) showed that the
consumption of fibre was lower than expected.  Young white males
(19 to 29 years) had the highest intake of 13 g/d, while older
black males (55 to 74 years) and middle-aged black females (30 to
54 years) had the lowest intake averaging 7.4 g/d.
Presumably people are consuming more fibre since that survey was
taking, but it is likely that the greater majority of people are
still not consuming enough.
A recent survey (Carlson, 1985) of vegetarians has shown:
        vegans                                  45 g/d
        vegetarians in general                  38 g/d
        omnivores                               22
Rather than simply "adding" refined fibre to one's current diet,
the better approach is to thinks in terms of a dietary change of
foodstuffs that simply include foods with more fibre and excludes
foods (like meat or dairy products) that have none.  Vegetarians
naturally do well in this respect :-)
If you think that you need more fibre in your diet, then consider
a dietary change that includes:
    1.  a greater consumption of fibre-rich legumes
    2.  increased consumption of fresh fruits and vegetables
    3.  replacement of refined cereals and flour products to ones
          made by whole grains.
Vegetarians have no problem in getting enough fibre, but some may
not be getting a great enough VARIETY of fibre due to an omission
or shortage one or two of the above three areas.  A bad practice
is to simply consume large amounts of a single source of purified
fibre. Better to simply eat a variety of fibre by simply eating a
variety of whole foods.  By ensuring that at least 60% of energy
is in the form of whole, complex carbohydrates the resulting
dietary patter will perforce increase present intakes of dietary
fibre.  Vegetarians, as we have seen, do well in this regard. :-)


Because definitional problems there are different ways to measure
fibre depending own what is being tested.  Earlier tables only
measure for crude fibre (cellulose & lignin) and did not measure
for the "noncellulosic polysaccharides like pectin,
hemicellulose, and other polysaccharides (e.g., gums, mucilages
and algal polysaccharides). The figures for total dietary fibre
in the following table may be larger than some other tables you
may have, but that may be due simply the following table being
more inclusive in what is being measured as "fibre".)


                        Total   Cellulose  Noncellulose   Lignin
                       dietary              poly-
                        fiber               saccharides
                      (g/100g)  (g/100g)    (g/100g)     (g/100g)
 white                   2.72       .71        2.01       trace
 whole meal              8.5       1.31        5.95        1.24
 broccoli                4.10       .85        2.92         .03
 beans, baked            7.27      1.41        5.67         .19
 cabbage (boiled)        2.83       .69        1.76         .38
 corn (canned)           5.68       .64        4.97         .08
 lettuce                 1.53      1.06         .47        trace
 onions (raw)            2.10       .55        1.55        trace
 peas (raw, frozen)      7.75      2.09        5.48         .18
 carrots (boiled)        3.70      1.48        2.22        trace
 tomato (fresh)          1.40       .45         .65         .30
 apple (flesh)           1.42       .48         .94         .01
 apples (peels           3.71      1.01        2.21         .49
 banana                  1.75       .37        1.12         .26
 peach (flesh & skin)    2.28       .2         1.46         .62
 pear (flesh)            2.44       .67        1.32         .45
 pear (peels)            8.59      2.18        3.72        2.67
 strawberries            2.12       .33         .98         .81
 strawberry jam         1.12       .11          .85         .15
Peanuts               9.30        1.69         6.40        1.21
 peanut butter         7.55       1.91         5.64       trace
     [adapted from Southgate et al., A guide to calculating
     intakes of dietary fiber.  J. HUM. NUTR., 1976, 30:303-13]
To put things in more practical terms, consider again the above
foods but this time in terms of the kinds of actual servings on
is more likely to consume at any one meal.


                       Serving           Serving   Total dietary
                        size             weight     fiber/serving
                                          (g)          (g)
 white                1 slice              23            .63
 whole meal           1 slice              23           1.96
 broccoli             1/2 cup              73           2.99
 beans, baked         1/3 cup              85           6.18
 cabbage (boiled)     1/2 cup              73           2.07
 corn (canned)        1/2 cup              83           4.72
 lettuce              1/2 cup              55            .84
 onions (raw)         2.25" onion         100           2.10
 peas (raw, frozen)   1/2 cup              73           5.66
 carrots (boiled)     1/2 cup              75           2.78
 tomato (fresh)       small tomato        100           1.40
 apple (flesh)        1 medium apple      141           2.00
 apples (peels        1 medium apple       11            .41
 banana               6" banana           100           1.75
 peach (flesh & skin) 1 medium peach      100           2.28
 pear (flesh)         1/2 medium pear      87           1.12
 pear (peels)         1/2 medium pear     11            .95
 strawberries        10 large berries     100           2.12
 strawberry jam       1 Tbsp               20            .22
Peanuts               1 Tbsp                9            .84
 peanut butter        1 Tbsp               15           1.13
     [adapted from Southgate et al., A guide to calculating
     intakes of dietary fiber.  J. HUM. NUTR., 1976, 30:303-13]
Anderson, J.(1986).  Fibre and health: An overview.  Nutr. Today,
Carlson et al. (1985).  A comparative evaluation of vegan,
     vegetarian and omnivore diets.  J. PLANT FOODS, 6:89-100
Health & Welfare Canada.  (1990).  NUTRITION RECOMMENDATIONS: THE
Kay & Truswell (1977).  Effect of citrus pectin on blood lipids
     and fecal steroid excretion in man.  AM. J. CLIN. NUTR.,
Kuhnlein et al. (1981).  Mutagens in feces from vegetarians and
     non- vegetarians.  MUTATION RES., 85:1-12.
McCance & Widdowson (1991), THE COMPOSITION OF FOODS, 5th ed.
Southgate, D. (1987).  Minerals, trace elements and potential
     hazards. AM. J. CLIN. NUTR., 45:1256-66.
Van Faasen et al. (1987).  Bile acids, neutral steroids, and
     bacteria in feces as affected by a mixed, a lacto-
     vegetarian, and a vegan diet.  AM. J. CLIN. NUTR., 46:962-
Van Soest (1984).  Some characteristics of dietary fibre and
     their influence on the microbial ecology of the human colon.
     PROC. NUTR. SOC., 43:25-33.