Carbohydrates are one of the most important food groups in the diet. They provide essential elements that the body needs for instant energy production and various vital functions.
Carbohydrates are classified according to their degree of polymerisation as follows:
- Simple sugars such as monosaccharides and disaccharides
- Longer chains of sugars called oligosaccharides
- Polysaccharides, which includes starch and non-starch polysaccharides
The main components of fibre are derived from plant cell walls and include the non-starch polysaccharides cellulose, hemicellulose and pectin.
Role of carbohydrates in health
Carbohydrates are an important source of energy, forming around 40% to 80% of our total energy intake. Several health organizations recommend carbohydrates should form the main source of energy over other food groups for the following reasons:
- Carbohydrates provide easily available energy for oxidative metabolism and energy production
- Carbohydrates help maintain a healthy blood sugar level
- Fibre is beneficial in maintaining normal and healthy gastrointestinal function
- Unlike fat and protein, a high carbohydrate intake is not linked to adverse health effects, providing the carbohydrates are derived form a variety of sources.
- Compared with diets rich in fat and protein, diets rich in carbohydrates reduce the risk of obesity and its associated conditions.
Sources of carbohydrates
Food sources that are rich in carbohydrates include cereals, root crops or tubers, sugar, pulses and legumes, vegetables, fruits and milk products. Grains and vegetables such as rice, wheat, maize, barley, potatoes, yams, cassava, and sweet potatoes are rich in starch.
Nuts, legumes and high-fibre grain or whole grains contain significant amounts of dietary fibre, about a third of which is present as hemicellulose. Around one-fourth of the fibre in grains and fruits and one third in nuts and vegetables is made up of cellulose. Pectin makes up about 15% to 20% of the content in legumes, nuts, fruits and vegetables. Added sugar in the diet is a small but important source of carbohydrates. Food sources that contain added sugar include fruit drinks, biscuits and desserts.
As per recommendations by the World Health Organization (WHO), the intake of total carbohydrate should be enough to provide 55% to 75% of the total energy requirement. Proteins should provide 10% to 15% and fats should provide 15% to 30% of the total energy. This requirement can be met by consuming a daily minimum of 400 grams of vegetables and fruits including 30 grams of pulses, nuts and seeds.
Reviewed by Sally Robertson, BSc