Introduction
Dietary carbohydrates (CHOs) provide the major
energy source in the diets of most people and
include a range of compounds which share the
common basic elements of carbon, hydrogen and
oxygen, and an empirical formula of (CH 2 O)n.
CHOs occurring naturally in foods, or more
recently, manufactured by special chemical tech-
niques and added during food processing, are
generally classified according to their chemical
structure. However, this system does not account
for the variety and overlap of functional, meta-
bolic and nutritional characteristics of ‘CHO
foods’. This chapter will describe briefly the
types of CHOs in our diets, and then focus on the
features of CHO-rich foods that may be of inter-
est to athletes and physically active people, justi-
fying the recommendations of many expert
nutrition bodies that we should further increase
our dietary CHO intake.
Structural classification of CHOs
Carbohydrates are classified according to the
degree of polymerization, or number of saccha-
ride units, in the CHO molecule. Table 5.1 lists
the various saccharide categories along with
examples of commonly consumed CHOs. The
main monosaccharides, glucose and fructose, are
present in fruits and vegetables, while fructose is
now provided in processed foods in increasing
amounts due to the use of high-fructose sweet-
eners derived from the chemical treatment of
corn starch. Sucrose is generally the most abun-
dant disaccharide in Westernized diets, with
foods providing naturally occurring and/or
added sources of this sugar, while lactose is pro-
vided primarily by dairy foods such as milk,
yoghurt and ice cream. Oligosaccharides make
up only a small amount of dietary CHO intake;
for example, raffinose, stachyose and verbascose
are unusual CHOs found in legumes, while
fructo-oligosaccharides appear in other vegeta-
bles. Glucose polymers, short chains of 3–15
glucose units commercially produced by the
chemical or enzymatic breakdown of starch,
have found a small dietary niche in processed
foods, including sports foods such as sports
drinks.
Starch is quantitatively the most important
food CHO, and may occur as amylose in which
the saccharide linkages are almost entirely
straighta-1,4 or linear bonds, or as amylopectin
in which a mixture of a-1,4 and a-1,6 bonds gives
a highly branched structure. Starch is the plant
storage CHO, and is found predominantly in
grains, legumes and some vegetables and fruit.
The non-starch polysaccharides (NSPs) include
structural cell wall components (hemicellulose
and cellulose, and pectins) as well as storage
polysaccharides, gums and mucilages. These
NSPs share the characteristic of being largely
undigested in the small intestine, and together
with lignin comprise ‘dietary fibre’. For further
review, see Asp (1995).