Dietary Fibre - ILSI Argentina

24 Concise Monograph Series
HEALTH BENEFITS
Introduction
Since the concept of dietary fibre was established three
to five decades ago, it has been suggested that an
insufficient consumption of dietary fibre contributes to a
plethora of chronic disorders such as constipation,
diverticulitis, haemorrhoids, appendicitis, varicose
veins, diabetes, obesity, cardiovascular disease and
cancer of the large bowel and various other cancers.
These hypotheses have been developed largely from
early observational studies. All these disorders have a
multifactorial aetiology and over time experimental
research has helped to refine our understanding of their
relationships with dietary fibre. This has shown that
only some of the proposed effects actually exist, but also
suggested that dietary fibre influences other processes of
significance for disease risk.
It is now evident that the individual components of
dietary fibre have different physiological effects and
therefore differing potential for disease risk reduction.
More recently claimed properties of potential
physiological significance are butyrate formation,
prebiotic properties and enhanced mineral absorption.
It is important to note that the use of dietary fibre as a
generic term and the use of different methodologies for
its measurement, notably the Englyst method for nonstarch
polysaccharides and the AOAC methods for total
dietary fibre, has complicated the interpretation of
observational studies in this area. In many cases it has
been impossible to disentangle whether the specific
components of dietary fibre have the postulated
physiological effects and health benefits, or whether it is
the total dietary pattern that is responsible.
Furthermore, evidence from well-controlled recent
studies suggests that the beneficial effects of dietary
fibre may not be due only to dietary fibre per se, and
that other components or properties of the dietary fibrecontaining
food also contribute.
Short chain fatty acids
Fermentation and physiological functions
Many dietary fibre components are partially or
completely fermented by the colonic microflora. This
adds to the body’s digestive capacity. The colon is
estimated to contain typically at least 400 different
anaerobic species of bacteria with total numbers of the
order of 10 12 per gram of colon contents. There is
considerable variation in bacterial species between and
within individuals, depending on factors such as age
and diet. Most of the bacteria in the human colon use
carbohydrates as an energy source, but not all species
can degrade the polysaccharides and some rely for their
substrate on the initial degradation products of other
species. The main fermentation pathway generates
pyruvate from hexose sugars in the undigested
carbohydrate. The colonic bacteria produce a wide
range of enzymes subsequently producing hydrogen,
methane, carbon dioxide, short chain fatty acids (mainly
acetate, propionate and butyrate) and lactate. The
bacteria generate energy and carbon from the
fermentation products. Therefore, dietary components
that stimulate fermentation lead to an increase in the
bacterial mass (biomass) and consequently in faecal
mass, that is, they have a stool bulking effect. It is
estimated that about 30 g of bacteria are produced for
every 100 g of carbohydrate that is fermented.
At both the local (colonic) and systemic levels,
fermentation has important physiological effects in
which the short chain fatty acids play a central role
(Box 4). Colonic epithelial cells demonstrate essential
metabolic activities. Butyrate is used preferentially as an