Monograph: |
Dietary fibre (Bran)
The fibrous outer layers of cereal grains, usually wheat, con-
sisting of the pericarp, testa, and aleurone layer. It contains
celluloses, polysaccharides or hemicelluloses. protein, fat,
minerals, and moisture and may contain part of the germ or
embryo. Bran provides water-insoluble fibre and. depending
on the source, may also provide water-soluble fibre.
It comprises about 12% of the weight of the grain and
is a byproduct of flour milling. It is available in various
grades.
Adverse Effects
Large quantities of bran may temporarily increase
flatulence and abdominal distension, and intestinal
obstruction may occur rarely. Interference with iron.
zinc, and calcium absorption has been reported; cal-
cium phosphate may be added to bran to neutralize
phytic acid. which can contribute to such interfer-
ence.
Diarrhoea. A report of diarrhoea induced by a dramatic in-
crease in fibre intake. Reduction of dietary fibre led to a
return
to normal bowel habit in 2 to 3 days.'
Intestinal obstruction. Intestinal obstruction associated
with excessive bran intake has been reported.'''
Precautions
Bran is contra-indicated in patients with intestinal
obstruction or with undiagnosed abdominal symp-
toms. Bran should not be eaten dry because of the
possibility of oesophageal or intestinal obstruction.
Interactions
Bran can bind to and reduce the absorption of a
number of drugs including cardiac glycosides and
salicylates when given concomitantly by mouth.
Uses and Administration
The main use of bran is as a source of dietary fibre
in the management of disorders of the gastro-intes-
tinal tract such as constipation , especially
in diverticular disease and the irritable
bowel syndrome . It should always be taken
with plenty of fluid.
It is used as the basis for some breakfast cereals.
There is no precise definition for the complex mixture of sub-
stances known as dietary fibre. It has been defined as plant
polysaccharides and lignin resistant to hydrolysis by the di-
gestive enzymes of man but this covers many substances oth-
er than cell wall and related polysaccharides. Non-starch
polysaccharides are the major component of the plant cell
wall and are used as an index of dietary fibre. They comprise
water-soluble fibres such as pectins, gums, and mucilages and
water-insoluble fibres such as cellulose: wheat, maize, and
rice contain mainly insoluble non-starch polysaccharides
whereas oats, barley, and rye have a significant proportion of
soluble fibres,
In the United Kingdom dietary reference values (DRV) have
heen published for non-starch polysaccharides, In the UK it
is proposed that adult diets should contain an average for the
population of 18 g daily (individual range 12 to 24 g daily)
non-starch polysaccharide from a variety of foods whose con-
stituents contain it as a naturally integrated component. Chil-
dren should receive proportionately less non-starch
polysaccharide according to body size. No evidence exists for
benefit of intakes of non-starch polysaccharide in excess of
32 g daily, and therefore there is no advantage in exceeding
lhis amount,
Discases such as colorectal cancer, ischaemic heart disease.
diabetes mellitus. and obesity are common in affluent West-
ern civilization but occur rarely in rural Africa. This differ-
ence in disease patterns has been linked to the low fibre intake
of Westerners compared with rural Africans. However, there
MC many other differences in diet and lifestyle. such as a low-
er intake of fat. protein, and sugar in rural Africans and less
exposure to toxins and pollutants, any of which could contrib-
ute to the difference. The excessive consumption of energy-
rich foods may be more to blame for diseases of Western civ-
ilisation than is deficiency of dietary fibre. Furthermore,
there is some concern that the use of fibre supplements is not
entirely without harmful effects: it has been pointed out that
fermentable fibre substrates can stimulate cell proliferation in
the colon However the role of cell proliferation as a marker
for the development of colonic cancer is questioned by some
authors.
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