One of the most important functions of digestible carbohydrates is providing energy and storing it. The following digestible carbohydrates are among those utilisable by humans: monosaccharide/monosugar (e.g. glucose, fructose, galactose), disaccharide/disugar (e.g. saccharose, lactose), oligosaccharide/polysugar (e.g. raffinose), and polysaccharide/multiplesugar (e.g. glycogen, starch).

Polysaccharides mainly serve as energy stores. For mammals, this is in the form of glycogen. For plants, it is in the form of starch. Oligosaccharides or disaccharides also perform this function, but much less frequently. In the main, they are all converted to and from glucose and used in cells for producing energy. Carbohydrates are stored in our muscles and liver in the form of glycogen. There they serve as quickly available energy reserves.

Carbohydrates are, apart from their function as energy providers, also a component in all biologically important structural components. They can be combined with proteins, in which case they are called glycoproteins. These fulfil numerous functions in the body. They are components of the immune system and cell membranes, and also participate in cell-cell interaction. Carbohydrates are also used, with non-essential amino acids or specific fatty acids, to build important molecules in the body. Even basic modules in our genetic make-up, such as glycolipids (also, glycosphingolipids) and nucleotides, possess some carbohydrates.

Sucrose (household sugar) is not only important for our body in its function as a carbohydrate, but also in its role as a taste-providing ingredient in chocolate. It is in fact the greatest source of carbohydrates in chocolate. In milk chocolate, lactose (milk sugar) is the second largest supply of carbohydrates.