From: altar@beaufort.sfu.ca (Ted Wayn Altar)
Subject: Fibre: Detoxification
Organization: Simon Fraser University, Burnaby, B.C., Canada
Date: Mon, 11 Jan 1993 08:43:01 GMT



VIII.  DETOXIFICATION

Microbial proliferation and excretion is not only important
for increasing fecal volume but is thought to play an
important role as a "DETOXIFICATION MECHANISM".

In 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 loves in the vegans and
vegetarians. volunteers showed.  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.

                                     ted

References:

Hunt & Groff's (1990), ADVANCED NUTRITION AND HUMAN
    METABOLISM, 1990.

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.

Kuhnlein et al. (1981).  Mutagens in feces from vegetarians
    and non-vegetarians.  MUTATION RES., 85:1-12.

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.,
    46:962-67.

IX.  POTENTIAL ADVERSE EFFECTS

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".

                                     ted

References:

Hunt & Groff's (1990), ADVANCED NUTRITION AND HUMAN
    METABOLISM, 1990.

Health & Welfare Canada.  (1990).  NUTRITION
    RECOMMENDATIONS: THE REPORT OF THE SCIENTIFIC REVIEW
    COMMITTEE.

Southgate, D. (1987).  Minerals, trace elements and
    potential hazards.  AM. J. CLIN. NUTR., 45:1256-66.