Dietary Fibre - ILSI Argentina

Dietary Fibre 27
starch appears to influence the fermentation of other
less well fermentable substrates in the large bowel.
Accordingly, resistant starch increases faecal excretion
of non-starch polysaccharides. Most studies have also
shown that resistant starch consumption increases
faecal butyrate and acetate concentration, and thus
decreases faecal pH. However, resistant starch does not
appear to influence gut transit time in humans.
Constipation
Traditionally considered as being the need to strain on
defaecation, constipation is defined variously in terms
of regularity of bowel movements, stool consistency
and stool weight. Various types of dietary fibre seem to
prevent and relieve this disorder. Increases in faecal
bulking and stool weight are important, but not the only
factors involved. Wheat bran has been shown to be
most effective in increasing faecal bulk, although
isolated cellulose is also effective and increases faecal
bulk to a greater extent than isolated fermentable fibres
such as pectin. However, all non-absorbed
carbohydrates may increase laxation through water
binding, osmotic effects of degradation products and
increasing bacterial mass. It has been estimated that
fibre intake should amount to 32-45 g/day in order to
reach a ‘critical ‘ faecal mass of 160-200 g/day needed to
minimise the risk of constipation.
Diverticulosis
Diverticulosis of the colon is characterised by
herniations in the colonic wall, which are normally
asymptomatic. They may cause pain when inflamed as
a result of bacterial action, a condition referred to as
diverticulitis. There is evidence from both observational
and intervention studies that dietary fibre intake
protects against the disorder and relieves symptoms.
Non-viscous fibres such as cellulose are particularly
effective in this respect, as are bran-containing cereal
foods. These protective effects may involve increased
stool weight, decreased transit time and decreased intracolonic
pressure.
Inflammatory bowel disease
Butyrate is formed and used more in the proximal colon
than in the distal colon. There is some evidence that a
lack of butyrate availability or oxidation is involved in
the pathogenesis of inflammatory bowel disorder, e.g.
ulcerative colitis in the distal colon. In some patients,
treatment with butyrate reduced inflammation. In
animal studies butyrogenic carbohydrates such as RS3
accelerate the resolution of inflammation. In vitro and
animal studies have shown that polydextrose is
fermented slowly throughout the colon and generates
butyrate in both the proximal and distal colon.
However, it is still uncertain whether consumption of
fibre that generates large amounts of butyrate is
efficacious in patients with ulcerative colitis.
Colorectal cancer and related factors
The effect of dietary fibre on cancer of the colon and
rectum has been the subject of controversy.
Carcinogenesis is a complex biological process that in
some cases results from inherited genetic mutations but is
also influenced by external factors including diet. Dietary
fibre has effects that could contribute to a reduction of the
risk of colorectal cancer. These effects include the dilution
and binding of carcinogens, changes in the profile of bile
salts within the colon, increased speed of gut transit and
effects of end products of fermentation of non-digestible
carbohydrates and analogous substances (inulin, fructooligosaccharides,
resistant starch, aleurone fibre and
wheat bran). Short chain fatty acids may modulate
expression of cell cycle-regulating proteins and induce