Dietary Fibre - ILSI Argentina

2 Concise Monograph Series
SUMMARY
Definitions and composition
The concept of dietary fibre has changed considerably
in recent years. It is now recognised that dietary fibre
encompasses a much broader range of substances than
was acknowledged previously and that it has greater
physiological significance than previously thought.
There is no generally accepted definition of dietary fibre
in Europe or worldwide. However, there is a consensus
that a physiologically based definition is necessary.
Non-digestibility in the small intestine is a key
physiological characteristic of dietary fibre. Recent
definitions of dietary fibre have therefore encompassed
– in addition to non-starch polysaccharides – other nondigestible
carbohydrates such as resistant starch and
non-digestible oligosaccharides. Research over recent
decades has identified the following main physiological
effects of dietary fibre: improvements in large bowel
function, lowering of blood cholesterol, and attenuation
of post-prandial blood glucose and insulin levels. These
physiological characteristics have been incorporated
into recent definitions of dietary fibre.
According to the more recent definitions, dietary fibre
consists of carbohydrate polymers and non-starch
polysaccharides that are primarily components of plant
cell walls. These include cellulose, hemicelluloses,
hemiglucans and pectins, as well as other polysaccharides
of plant and algal origin, such as gums and
mucilages. Other components included are indigestible
storage polysaccharides such as inulin and resistant
starch. Recent definitions also encompass analogous nondigestible
carbohydrates that pass through the small
intestine unchanged. Examples of such are resistant
starch, resistant maltodextrins, fructo-oligosaccharides
and galacto-oligosaccharides, as well as modified
celluloses and synthesised carbohydrate polymers such
as polydextrose. They furthermore include associated
substances such as lignin and other substances extracted
with the polysaccharides and oligosaccharides in fibre
analytical methods (e.g. waxes, cutin, polyphenols and
phytosterols). The latest definition proposed by Codex
Alimentarius includes carbohydrate polymers with a
degree of polymerisation not lower than 3. They can be
naturally present in or extracted from food raw material,
or synthesised. The debate continues and some recent
opinion has favoured a return to the original fibre
definition along the lines that 'Dietary fibre consists of
intrinsic plant cell wall polysaccharides'.
Analysis
The basis for both legal definitions and analysis of
dietary fibre is, in many cases, the enzymatic,
gravimetric methods approved by the Association of the
Official Analytical Chemists (AOAC). However, dietary
fibre as now defined cannot be measured by a single
method of analysis because of the diversity of its
constituents. For instance, the standard method or any
other method for analysis of dietary fibre or non-starch
polysaccharides does not measure oligosaccharides that
are soluble in alcohol. Furthermore, in some cases, e.g.
in the UK, food manufacturers tend to use AOAC
whereas composition tables and dietary intake
recommendations tend to be based on data produced
with the Englyst method.
Consumption
Methods of data collection and analysis influence
estimates of dietary fibre consumption. This limits
comparison between different countries and
populations. As yet there is even more limited