By definition, carbohydrates are organic compounds that consist only of hydrogen, oxygen, and carbon, with hydrogen and oxygen in the 2:1 ratio. Carbohydrates, protein, and fats are the most important elements for a human being's good nutrition. One gram of carbohydrate contains around 3.75 calories of energy (or 106 calories per ounce). Carbohydrates are broken down and classified into "simple" and "complex" carbohydrates. Foods high in simple carbohydrates include fruits, sugars, sweets, and soft drinks. Foods made mainly from rice, wheat, corn, potatoes, and beans, such as breads, pastas, noodles, etc., are high in complex carbohydrates. Nutritionists generally recommend complex carbohydrates, and nutrient-rich simple carbohydrate food, such as fruit (glucose or fructose) and dairy products (lactose) for the bulk of carbohydrate consumption. Simple sugars, such as candy and sugary drinks, are generally not recommended.
Based on the effects on risk of heart disease and obesity, the Institute of Medicine recommends that American and Canadian adults get 40% to 65% of their dietary energy from carbohydrates. The Food and Agriculture Organization and the World Health Organization jointly recommend that national dietary guidelines set a goal of 55% to 75% of total energy from carbohydrates, but only 10% directly from sugars (their term for simple carbohydrates).