All living organisms need energy to survive and carbohydrates are the main energy source for many of them.
Carbohydrates are a cheap energy source and depending on the socio-economic situation, culture and habits, carbohydrates can provide more than 60% of the energy needed by humans; they account for 4 kilocalories per gram.
Why do we need carbohydrates?
Although carbohydrates represent a large part of the human diet, they are not considered to be essential. Theoretically the body can synthesize enough carbohydrates for its basic needs. We need carbohydrates for immediate energy and the glycogen stores that we constitute with the surplus are also rapidly available.
Glucose is the primary source of energy for the brain that needs an average of 125 g glucose per day. If no glucose is supplied by the diet, 40% will be synthesized from lipids and 60% from proteins. However this process is very expensive in term of energy and particularly proteins should be kept for a better usage i.e. growth, structure and maintenance. Therefore carbohydrates are a major part of our diet.
How much do we need?
It is recommended that carbohydrates represent around 55% of calories intake, if possible mainly from unrefined sources.
What are the sources in our diet?
The best natural sources of sugar are fruits and vegetables; grains, tubers and legumes are great sources of starch and other polysaccharides.
In many countries most of dietary carbohydrates are provided by staple foods such as rice, corn or tubers. But in the western affluent societies, a large part of carbohydrates comes from refined sugar found in sweetened beverages, breakfast cereals, jams, candies, ketchup etc…
Carbohydrates in human nutrition. Report of a joint FAO/WHO Expert Consultation, FAO Rome, 1998.
Essentials of Human Nutrition, J. Mann and A. S. Truswell Editors. Oxford University Press, 2012