Sugars and starches
in food are sources of energy. Australians obtain 20 to 60 per cent
of their total dietary energy from carbohydrate. Cellulose and some
related substances are not used by our bodies as a significant source
of energy. Nevertheless, these components are very important as, together
with other indigestible substances, they constitute dietary fibre.
The role of dietary fibre is discussed on Chart
The main sugars
in food are sucrose, glucose, fructose, maltose and lactose. Sucrose
is obtained from sugar cane and is usually called 'sugar'. In addition,
sucrose (as well as glucose and fructose) is found in fruit, fruit
juices and honey. Besides providing energy, sugars also produce the
sensation of sweetness. Each sugar contributes the same amount of
energy (kilocalories) to our diet regardless of its sweetness. Different
sugars are not equally sweet and the degree of sweetness of a food
is often not a good indication of the amount of sugars present. For
example, as shown in Figure 45, maltose is only
half as sweet as sucrose.
45: SWEETNESS OF SUGARS RELATIVE TO SUCROSE
Sugars are widely
distributed in foods, particularly processed foods where their sweetness
may sometimes be masked or hidden by other ingredients. Often the
list of ingredients on the label will give an indication of the relative
amount of sugar present. For a fuller discussion on sugars, see
Sugars and Health.
The use of non-nutritive
or artificial sweeteners can be used to make food and drink sweet
without contributing significant amounts of energy. Although there
is controversy about their safety, the most widely used artificial
sweeteners are saccharin and cyclamate. The label of any food or drink
containing these sweeteners must indicate that they are present. An
artificial sweetener recently approved by some health authorities
is aspartame. It has about the same energy value as sugar but because
it is 180 times sweeter, very little needs to be used. The amount
of aspartame providing sweetness equivalent to one teaspoon of sugar
will only provide one-tenth of a kilocalorie.
Starch is the
main form of carbohydrate in our food. It is present in a variety
of cereals, vegetables and fruit, with major contributions from flour,
potatoes and legumes (beans, peas). Starchy foods are usually cooked
to improve digestibility and give a more desirable texture and flavour.
During the ripening of fruit, starch is changed into sugars, which
give sweetness to ripe fruits. In contrast to sugars, starch is often
accompanied by significant amounts of other nutrients including dietary
fibre. Starch has the same energy value as sugars. Health authorities
are in agreement that we should increase our consumption of foods
containing starch, such as wholegrain bread, cereals, fruits, vegetables
There is no specific
dietary requirement for carbohydrate because energy can also be derived
from protein, fat and alcohol. However, a diet that does not contain
carbohydrate can lead to muscle breakdown, ketosis and dehydration.
This can be prevented by 50 to 100 grams of carbohydrate per day,
but levels above this are desirable. Sources of complex carbohydrates,
such as starch, are recommended as these often also provide necessary
vitamins, elements (minerals) and dietary fibre.