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CARBOHYDRATES AND NUTRITION
There have been major advances in the understanding of how carbohydrates
influence human nutrition and health in recent years. Progress in scientific
research has highlighted the diverse functions of carbohydrates in the
body and their importance in the promotion of good health. In fact,
there is so much good news that it is time to take a closer look at
carbohydrates.
The Importance Of Carbohydrates
Carbohydrates take the form of sugars, oligosaccharides, starches and
fibres and are one of the three major macro-nutrients which supply the
body with energy (fat and protein being the others). There is now good
evidence that at least 55% of our daily calories should come from carbohydrates(1).
Whereas it is important to maintain an appropriate balance between calorie
intake and expenditure, scientific studies suggest that:
- a diet containing an optimum level of carbohydrates may help prevent
body fat accumulation
- starch and sugars provide readily accessible fuel for physical performance
- dietary fibre, which is a carbohydrate, helps keep the bowel functioning
correctly.
Apart from the direct benefits of carbohydrates for the body, they
are found in a wide range of foods which themselves bring a variety
of other important nutrients to the diet. For this reason it is recommended
that carbohydrates be supplied from diverse food sources to ensure that
the overall diet contains adequate nutrients(1). It is also important
to remember that carbohydrates contribute to the taste, texture and
appearance of foods and help to make the diet more varied and enjoyable.
What are Carbohydrates?
The building blocks of all carbohydrates are sugars and they can be
classified according to how many sugar units are combined in one molecule.
Sugars
Glucose and fructose are simple sugars or monosaccharides and can be
found in fruits, berries, vegetables and honey. When two simple sugars
combine, they form disaccharides. Table sugar or sucrose is a combination
of glucose and fructose and occurs naturally both in sugar beet, sugar
cane and fruits. Lactose is the main sugar in milk and dairy products
and maltose is a disaccharide occurring in malt. Polyols are so-called
sugar alcohols. They do occur naturally but most are made commercially
by the transformation of sugars. Isomalt is the most commonly used polyol
and is derived from sucrose. Polyols are sweet and can be used in foods
in a similar way to sugars although they can have a laxative effect
when eaten in large quantities.
Oligosaccharides
When 3-9 sugar units combine they form oligosaccharides. Maltodextrins
contain up to 9 glucose units and are produced commercially by the partial
hydrolysis (or breakdown) of starch. They are less sweet than mono-
or disaccharides. Raffinose, stachyose and fructo-oligosaccharides are
found only in small amounts in certain pulses, grains and vegetables.
Polysaccharides
More than 10 and sometimes even up to several thousand sugar units are
needed to form polysaccharides. Starch is the main energy reserve in
root vegetables and cereals. It comprises long chains of glucose and
occurs as granules whose size and shape vary according to the plant
in which it is contained. Non-starch polysaccharides are the main components
of dietary fibre. They include; cellulose, hemicelluloses, pectins and
gums. Cellulose is the major component of plant cell walls and consists
of several thousand glucose units. The separate components of dietary
fibre have different physical structures and properties.
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