The primary function of carbohydrates is to provide energy for the body, especially the brain and the nervous system. An enzyme called amylase helps break down carbohydrates into glucose (blood sugar), which gives your body energy.
Carbohydrates are classified as simple or complex. This classification depends on the chemical structure of the food, and how quickly the sugar in the food is digested and absorbed. Simple carbohydrates have one (single) or two (double) sugars. Complex carbohydrates have three or more sugars.
Examples of single sugars from foods include:
Fructose (found in fruits)
Galactose (found in milk products)
Double sugars include:
Lactose (found in dairy)
Maltose (found in certain vegetables and in beer)
Sucrose (table sugar)
Honey is also a double sugar. But unlike table sugar, it contains a small amount of vitamins and minerals. (Note: Honey should never be given to children younger than 1 year.)
Simple carbohydrates that contain vitamins and minerals occur naturally in:
Milk and milk products
Simple carbohydrates are also found in processed and refined sugars such as:
Regular (non-diet) carbonated beverages, such as soda
Refined sugars provide calories, but they lack vitamins, minerals, and fiber. Such simple sugars are often called "empty calories" and can lead to weight gain.
Also, many processed and refined foods, such as white flour, sugar, and white rice, lack B vitamins and other important nutrients unless they are marked "enriched." It is healthiest to eat carbohydrates, vitamins, and other nutrients in the most natural form possible -- for example, from fruit instead of table sugar.
Complex carbohydrates, often referred to as "starchy" foods, include:
Legumes, such as beans, peas, lentils and peanuts
Starchy vegetables, such as potatoes, corn, green peas, and parsnips
Whole-grain breads and cereals
Eating too many carbohydrates can lead to an increase in total calories, which can lead to obesity.
Not eating enough carbohydrates can cause a lack of calories (malnutrition), or lead to an excessive intake of fats to make up for the calories not eaten as carbohydrates.
Most people should get between 40 to 60% of their total daily calories from carbohydrates. It is best to get most of these calories from complex carbohydrates (starches) and natural sugars. In addition to calories, complex carbohydrates provide vitamins, minerals, and fiber.
To increase your intake of complex carbohydrates and healthy nutrients:
Eat fruits and vegetables.
Eat whole-grain rice, breads, and cereals.
Eat legumes (beans, lentils, and dried peas).
Here are recommended serving sizes for foods that are high in carbohydrates:
Vegetables: 1 cup of raw vegetables, or 1/2 cup cooked vegetables, or 3/4 cup of vegetable juice
Fruits: 1 medium-size fruit (such as 1 medium apple or 1 medium orange), 1/2 cup of a canned or chopped fruit, or 3/4 cup of fruit juice
Breads and cereals: 1 slice of bread; 1 ounce or 2/3 cup of ready-to-eat cereal; 1/2 cup of cooked rice, pasta, or cereal; 1/2 cup of cooked dried beans, lentils, or dried peas
Dairy: 1 cup of skim or low-fat milk
For information about how many servings are recommended, see the article on the food guide plate.
Here is a sample 2,000 calorie menu that contains 50 to 60% of its total calories from carbohydrates:
1 cup shredded wheat cereal, topped with 1 tbsp. raisins and one cup fat-free milk
1 small banana
1 slice whole-wheat toast
1 tsp. soft margarine
1 tsp. jelly
Smoked turkey sandwich, made with 2 ounces whole-wheat pita bread, 1/4 cup romaine lettuce, 2 slices tomato, 3 ounces sliced smoked turkey breast
1 tbsp. mayonnaise-type salad dressing
1 tsp. yellow mustard
1/2 cup apple slices
1 cup tomato juice
5 ounces grilled top loin steak
3/4 cup mashed potatoes
2 tsp. soft margarine
1/2 cup steamed carrots
1 tbsp. honey
2 ounce whole-wheat dinner roll
1 tsp. soft margarine
1 cup. fat-free milk
1 cup low-fat fruit yogurt
Dietary Guidelines for Americans 2010. 7th ed. Rockville, MD: United States Department of Health and Human Services and United States Department of Agriculture; 2010.
Farrell JJ. Digestion and absorption of nutrients and vitamins. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger & Fordtran’s Gastrointestinal and Liver Disease. 9th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 100.
Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.