One gram of carbohydrates contains 4 calories. One gram of protein contains 4 calories, and one gram of fat contains 9 calories. The U.S. Department of Agriculture recommends that between 45 and 65 percent of total daily calories come from carbohydrates.
Carbohydrates can come from simple sugars, complex starches and fiber. Fruit, beans, grains and vegetables all contain carbohydrates, as do sweet items, such as candy, cake and cookies. Carbohydrates fuel the brain and are the main source of energy for the human body. It is recommended to eat carbohydrates from nutritious foods, including fruit, vegetables and whole grains, with limited intake from junk foods, such as cookies and cakes.