Carbohydrates are an important source of energy. They include sugars, starches, and fiber. Sugars are small, simple carbohydrates like glucose, fructose, and galactose. Starches are complex carbohydrates made of linked glucose units. Fiber is a type of carbohydrate that the body cannot digest. The body breaks down carbohydrates into glucose for energy or stores them as glycogen in the liver and muscles. A balanced diet should obtain about 40-60% of calories from carbohydrates to fuel the body and brain. Too little or too much carbohydrate intake can impair health.