Carbohydrates

Definition

Carbohydrates are one of the main dietary components. This category of foods includes sugars, starches, and fiber.

Overview & Functions

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 is used for energy by the body.

Food Sources

Carbohydrates are classified as simple or complex. The classification depends on the chemical structure of the food, and how quickly the sugar 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 not be given to children younger than 1 year old.)
Complex carbohydrates, often referred to as "starchy" foods, include:

• Legumes
• Starchy vegetables
• Whole-grain breads and cereals

Simple carbohydrates that contain vitamins and minerals occur naturally in:

• Fruits
• Milk and milk products
• Vegetables

Simple carbohydrates are also found in processed and refined sugars such as:

• Candy
• Regular (non-diet) carbonated beverages, such as soda
• Syrups (not including natural syrups such as maple)
• Table sugar

Refined sugars provide calories, but lack vitamins, minerals, and fiber. Such simple sugars are often called "empty calories" and can lead to weight gain.
Also, many refined foods, such as white flour, sugar, and polished rice, lack B vitamins and other important nutrients unless they are marked "enriched." It is healthiest to get carbohydrates, vitamins, and other nutrients in as natural a form as possible -- for example, from fruit instead of table sugar.

Complex carbohydrates 

 

Complex carbohydrates are made up of sugar molecules that are strung together in long, complex chains. Complex carbohydrates are found in foods such as peas, beans, whole grains, and vegetables. Both simple and complex carbohydrates are turned to glucose (blood sugar) in the body and are used as energy. Glucose is used in the cells of the body and in the brain. Any unused glucose is stored in the liver and muscles as glycogen for use later. Complex carbohydrate foods provide vitamins, minerals, and fiber that are important to the health of an individual. The majority of carbohydrates should come from complex carbohydrates (starches) and naturally occurring sugars, rather than processed or refined sugars, which do not have the vitamins, minerals, and fiber found in complex and natural carbohydrates. Refined sugars are often called "empty calories" because they have little to no nutritional value. Simple carbohydrates    Simple carbohydrates are broken down quickly by the body to be used as energy. Simple carbohydrates are found naturally in foods such as fruits, milk, and milk products. They are also found in processed and refined sugars such as candy, table sugar, syrups, and soft drinks. The majority of carbohydrate intake should come from complex carbohydrates (starches) and naturally occurring sugars rather than processed or refined sugars. Starchy foods    All food that you eat turns to sugar in your body. Carbohydrate-containing foods alter your sugar levels more than any other type of food. Carbohydrates are found in starchy or sugary foods, such as bread, rice, pasta, cereal, potatoes, peas, corn, fruit, fruit juice, milk, yogurt, cookies, candy, soda, and other sweets. Recommendations Most people should get between 40% and 60% of total calories from carbohydrates, preferably from complex carbohydrates (starches) and natural sugars. Complex carbohydrates provide calories, vitamins, minerals, and fiber. Foods that are high in processed, refined simple sugars provide calories, but very little nutrition. It is wise to limit these sugars. To increase complex carbohydrates and healthy nutrients: Eat more fruits and vegetables. Eat more whole-grain rice, breads, and cereals. Eat more legumes (beans, lentils, and dried peas). Here are recommended serving sizes for foods 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 dry beans, lentils, or dried peas Dairy: 1 cup of skim or low-fat milk For information about how many servings are recommended, see the food guide pyramid. Here is a sample 2,000 calorie menu, of which 50% - 60% of the total calories are from carbohydrates. Breakfast Cold cereal 1 cup shredded wheat cereal 1 tbsp raisins 1 cup fat-free milk 1 small banana 1 slice whole-wheat toast 1 tsp soft margarine 1 tsp jelly Lunch Smoked turkey sandwich 2 ounces whole-wheat pita bread 1/4 cup romaine lettuce 2 slices tomato 3 ounces sliced smoked turkey breast 1 tbsp mayo-type salad dressing 1 tsp yellow mustard 1/2 cup apple slices 1 cup tomato juice Dinner Grilled top loin steak 5 ounces grilled top loin steak 3/4 cup mashed potatoes 2 tsp soft margarine 1/2 cup steamed carrots 1 tbsp honey 2 ounces whole-wheat dinner roll 1 tsp soft margarine 1 cup fat-free milk Snacks 1 cup low-fat fruited yogurt Side Effects Getting too many carbohydrates can lead to an increase in total calories, causing obesity. Not getting enough carbohydrates can cause a lack of calories (malnutrition), or excessive intake of fats to make up the calories. References Farrell JJ. Digestion and Absorption of Nutrients and Vitamins. In: Feldman M, Friedman LS, Sleisenger MH, eds. Sleisenger & Fordtran's Gastrointestinal and Liver Disease. 8th ed. Philadelphia, Pa: WB Saunders; 2006:chap 97. Dietary Guidelines for Americans 2005. Rockville, MD: US Dept. of Health and Human Services and US Dept. of Agriculture; 2005.