What Are Two Major Kinds of Complex Carbohydrates?

Carbohydrates are one of the three essential macronutrients -- which include fat and protein -- and its primary role in your diet is to provide your body with energy. Carbohydrates are so important to your health that they should make up the bulk of your calorie intake, 40 to 60 percent. Carbohydrates are divided into two groups, simple and complex, based on their chemical structure. Complex carbohydrates contain longer chains of sugar than simple carbohydrates and require more effort for digestion. Two major complex carbohydrates include starch and cellulose.

A bowl of sliced potatoes. (Image: lauraag/iStock/Getty Images)

Starch

Starch is a type of carbohydrate found only in plant foods. Starch is made up of long straight chains of sugar, called amylose, or branched chains called amylopectin. Plant foods contain higher amounts of amylopectin to amylose, but the amounts of each vary from plant to plant. Starches are encased in plant cells by cellulose, and cannot be dissolved in cold water. But heating starches softens the cell wall and causes it to rupture, making the starch accessible for digestion.

Food Sources of Starch

Starches are the primary carbohydrate found in cereal grains, such as wheat, rice and oats. It is also the predominant carbohydrate in starchy vegetables like potatoes, beans and peas. When you eat starchy foods, your body works to break them down into glucose. Glucose is the sugar your body uses at its source of energy. The glucose not only helps you physically, but is also the primary source of fuel for your organs, including your brain, kidneys and muscles.

Cellulose

Cellulose makes up the cellular framework of plants. It is made up of unbranched glucose molecules in a long chain similar to amylose. However, the links between the glucose molecules in the cellulose is much stronger, making it more resistant to breakdown, and harder to digest. Hemicellulose is a type of cellulose that has fewer glucose molecules on its chain, and can also form shapes such as hexoses and pentoses.

Food Sources of Cellulose

Cellulose is only found in plant foods. Sources include the skin of fruit, the stalk of vegetables and the outer covering of grains, seeds and nuts. Your body cannot digest cellulose because it lacks the enzymes needed to break it down. Cellulose is the fiber in plant foods. Fiber in food helps move food through your digestive tract and adds bulk to stool. It improves satiety, helping to control hunger. Cellulose also acts as a source of fuel for the friendly bacteria found in your small intestines.

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