Carbohydrates are simply chains of single sugar molecules hooked together.
The three most common ones in our food supply are glucose, fructose, and galactose. Starches are one category of complex carbohydrates. Carbohydrates are the body's preferred and main source of fuel or energy. The body can store extra carbohydrate in the liver as glycogen. It can also change extra carbohydrate to fat and store it for later use.