Carbohydrates are complex biochemical structures that serve vital functions in the human body. Composed of a building block of sugar, they are the main source of energy for the body. There are many types of carbohydrates. One or more sugars will link together to form carbohydrates of different types. Complex carbohydrates consist of thousands of repeating sugar units and are the major constituent of starch. Nucleotides such as DNA are also composed of carbohydrates.

Ubiquitous in the natural environment, carbohydrates perform important bodily functions. Among the most important are regulation of blood glucose and provision of energy for the body. In addition, carbohydrates spare the use of proteins for energy until the body is completely depleted of carbohydrate stores. They can be used as flavorings and sweeteners and are a source of dietary fiber. Their composition is complex and their function essential.