Dietary Fibre - ILSI Argentina

Dietary Fibre 31
Satiety and body weight
Obesity is a rapidly escalating public health problem
throughout the western world and, more recently, even
in developing countries. Foods rich in dietary fibre tend
to be bulky and have a low energy density. Therefore, it
is contended that dietary fibre could promote satiation
and satiety and play an important role in the control of
energy balance and body weight. This is supported by
observational prospective data showing a negative
association between dietary fibre consumption and body
mass index, percentage of body fat and body weight.
There are indications that whole grains may also assist in
the regulation of body weight. Furthermore, it is
suggested that foods with a low GI are more satiating
than high–GI foods.
Intervention trials indicate that gastric emptying may be
delayed by the consumption of viscous (soluble) fibres
such as pectins. Most important, however, seem to be the
effects that occur in the small intestine. By forming gels,
these types of dietary fibre expand the unstirred layer
and slow the absorption of carbohydrates from the small
intestine by making them less accessible to digestive
enzymes and reducing contact with the intestinal
mucosa. This seems to extend the sensation of fullness.
There is also some evidence that the prolonged presence
of nutrients in the upper intestine promotes satiety.
Improved mineral availability
The large intestine is a poorly recognised site of mineral
absorption. In animal and some human studies the
colonic fermentation of non-digestible carbohydrates,
such as non-digestible oligosaccharides, improved the
absorption of minerals such as calcium, magnesium and
iron. This could have positive implications, such as
increasing bone density. Several mechanisms for
enhanced mineral absorption have been proposed. The
presence of short chain fatty acids, generated by the
fermentation of these substances, reduces the pH of the
colonic contents, thereby increasing the solubility of
calcium, making it more available for passive diffusion
across the colonic epithelium. It has also been suggested
that butyrate and polyamines (metabolites of various
microbial strains), both of which have the potential to
stimulate cell growth, indirectly expand the gut’s
absorptive area and increase the quantity of mineral
transport proteins. This would increase the proportion
of minerals absorbed. However, it is not faecal but
colonic pH which is the most important mechanism (as
evidenced by faecal pH).
It is too early to say whether fermentable dietary fibre
improves overall mineral status and bone health in
humans. Consequently, this physiological characteristic
has not yet been included in definitions of dietary fibre.
Research on the effects of different types of dietary fibre
on appetite, energy and food intake has not shown
consistent results. The findings differ according to the
type of dietary fibre and according to whether it is
added as an isolated dietary fibre supplement rather
than naturally occurring in food sources. Large
amounts of total dietary fibre (30 g/meal) may reduce
the energy intake, not only in a meal that contains such
an amount, but also in subsequent meals. The longerterm
relevance of these effects is not yet clear.