benefits via this process and the subsequent
release of short chain fatty acids. While some
components of dietary fibre are responsible for
adding faecal bulk and enhancing regularity,
various types of dietary fibre offer other appar-
ent health benefits related to glycaemic control,
lipid metabolism, weight control and reduced
risk of colonic cancer (for review, see Baghurst
et al. 1996).
Finally, the issue of dental caries is also
complex and cannot be entirely explained by the
consumption of sucrose and foods rich in simple
CHOs. Starch also provides a source of fer-
mentable CHO for the development of caries,
and the frequency of intake of CHOs and the
physical form of the CHO food/drink which
determines the length of time of adhesion to the
teeth are important factors in the aetiology of
dental decay. Other aetiological factors include
fluoride, oral hygiene practices and salivary flow
(for review, see Navia 1994).
Glycaemic index
In recognition of the lack of uniformity and the
inability to predict blood glucose responses to
the consumption of various CHO-rich foods, the
concept of the glycaemic index was introduced
by Jenkins in the early 1980s (Jenkins et al. 1981).
The glycaemic index is a ranking of foods based
on their actual postprandial blood glucose
response compared to a reference food, either
glucose or white bread. The glycaemic index is
calculated by measuring the incremental area
under the blood glucose curve following the
ingestion of a portion of the test food providing
50 g of CHO, compared with the area under the
blood glucose curve following an equal CHO
intake from the reference food, with all tests
being conducted after an overnight fast. Tables of
the measured glycaemic index of various CHO-
rich foods have now been published interna-
tionally (Foster-Powell & Brand-Miller 1995).
Thorough research in this area has shown that
the glycaemic index has acceptable reproducibil-
ity within and between individuals and can be
applied to a mixed meal containing CHO-rich
foods (for reviews, see Wolever 1990; Truswell
1992).
Many factors influence the glycaemic index of
CHO-rich foods including the food form (e.g.
particle size due to degree of milling or process-
ing, texture and viscosity including the presence
of soluble fibres) and the degree of food process-
ing and cooking (e.g. degree of gelatinization or
retrograding of starch, disruption to the cell
structure). The presence of fructose or lactose,
and the ratio of amylopectin to amylose in
starch are important, as are the presence of
starch–protein or starch–fat interactions, or com-
pounds known as ‘antinutrients’ (e.g. phytates,
lectins). Finally, even the ripeness of some fruits
such as bananas (i.e. degree of conversion of
starches to sugars) may affect their glycaemic
index (see Wolever 1990).
Table 5.3 summarizes the glycaemic index of
some common CHO-rich foods, and illustrates
the impossibility of predicting the glycaemic
index of a food based simply on its composition.
The glycaemic index concept has been used to
manipulate the glucose and insulin response to
diets of equal CHO content; lowering the gly-
caemic index has been shown to improve the
metabolic profiles of individuals with diabetes
and hyperlipidaemia (Wolever et al. 1991) and to
increase postmeal satiety (Holt et al. 1992). Thus
the glycaemic index has gained recognition as a
useful education tool in the management of dia-
betes and hyperlipidaemias.
More recently, it has been suggested that the
manipulation of the glycaemic index of meals or
the diet may have application in the area of
sports nutrition to optimize CHO availability for
exercise; high glycaemic index CHO-rich meals
have been reported to enhance the storage of
muscle glycogen during recovery from pro-
longed exercise compared with CHO-rich foods
of low glycaemic index (Burkeet al. 1993). CHO-
rich drinks or foods with moderate to high gly-
caemic index have been suggested as the most
appropriate source of CHO intake during pro-
longed exercise (Coyle 1991); whereas there has
been some publicity (Thomas et al. 1991), but not
universal agreement (Febbraio & Stewart 1996),