Carbohydrates are a class of organic molecules containing a carbonyl group (aldehyde or Ketone) and several hydroxyl groups (-OH). Carbohydrates were historically called carbohydrates. Their chemical formula is based on the model Cn (H2O) p (hence the title history). However, this model is not valid for all carbohydrates, which provide for some atoms of nitrogen or phosphorus (for example). They belong, along with proteins and lipids, essential constituents of living things and their nutrition because they are a key biological intermediate storage and consumption of energy. In Autotrophic organisms, like plants, sugars are converted into starch for storage. In heterotrophic organisms, like animals, they are stored as glycogen and used as a source of energy in metabolic reactions, they are oxidized during digestion of carbohydrates providing approximately 17 kJ / g depending on the study in the bomb calorimeter .