The primary role of carbohydrates is to supply the body’s cells with glucose, which is the basic unit of carbohydrates and an important energy source. Nearly all of the energy required by the brain to function each day is supplied by glucose from the diet. Carbohydrates also maintain blood glucose levels and have a role in gastrointestinal health.
When carbohydrates are eaten, they are broken down into glucose which is circulated to all parts of the body via the blood as an energy source. Any glucose that is not required immediately is stored in the liver and muscles as glycogen. Additional glucose is stored as fat.
Classification of carbohydrates
Carbohydrates are composed of sugar molecules made up of carbon with hydrogen and oxygen, and are classified based on their structure.
At one stage, simple sugars were considered the 'bad' carbohydrates and complex carbohydrates the 'good' carbohydrates. It is now realised that a balance of both groups is required for a healthy diet.
Monosaccharides and disaccharides are known as simple sugars because the body quickly digests them. Examples of foods containing simple sugars are sweet-tasting foods, but also fruit and vegetables.
Also known as polysaccharides, these compounds are made up of long chains of monosaccharides, usually glucose. Examples are compounds such as starch and glycogen. Foods containing complex sugars are breads, noodles, rice and vegetables.
Recommended daily intakes for carbohydrates
One gram of carbohydrate gives 16 kJ or 3.75 calories of energy. At least half the energy in our diets should come from carbohydrate, mostly as complex carbohydrates. Sucrose (sugar) and other free sugars found in syrups and juices should be restricted to less than 10% of this energy because of the problems of excess energy intake.
Food sources for carbohydrate
Good sources of carbohydrate include grains, starchy vegetables, legumes and wholegrain cereals, all of which contain at least 3-15% complex carbohydrates. At least six servings of breads and cereal per day and at least three of vegetables and fruit per day are required to achieve a desirable carbohydrate intake.