Carbohydrates are abundant in nature, existing in both plants and animals. They have a number of functions, serving as structural and messenger components of cells. The primary role of carbohydrates in the diet is to provide energy. The two main classes of dietary carbohydrates are simple sugars and complex sugars. Fiber is a third type of carbohydrate. Nondigestible by humans, fiber is not a source of energy, but it does provide numerous health benefits.
Simple Sugars
Simple sugars include monosaccharides and disaccharides. Glucose and fructose are the principal monosaccharides found in food. Glucose is abundant in fruits, sweet corn, corn syrup and honey. Fructose is found together with glucose in honey and in fruits. Disaccharides are sugar pairs and include sucrose, lactose and maltose. Sucrose consists of glucose and fructose. Also known as "table sugar," it is abundant in sweeteners such as molasses and maple syrup. Lactose is the principal sugar found in milk. Maltose is found in significant quantities in beer and malt liquors. It is also a product of the digestion of complex sugars.
Complex Sugars
Complex carbohydrates, also known as polysaccharides, are long chains of glucose. Unlike simple sugars, complex sugars do not have a sweet taste. Starch is an example of a complex carbohydrate that is found abundantly in plants. Common sources include wheat and other grains, such as barley, rice and oats. Additionally, potatoes, dried peas and beans and starchy vegetables such as yams and squash contain large quantities of starch.
Fiber
Dietary fiber is defined as the nondigestible carbohydrates and lignin present in plants. Fiber cannot be broken down by the human intestines and therefore does not supply any calories. However, fiber aids digestive function, helping move food through the intestines. Additionally, soluble fiber, found in oats and legumes, can lower cholesterol levels and normalize blood sugar. Insoluble fiber, present in such foods as raspberries and Brussels sprouts, helps prevent constipation and intestinal disorders, such as diverticulitis.
Glycogen
Glycogen is a storage form of carbohydrate. Like starch, glycogen consists of long chains of glucose molecules. Unlike starch, glycogen is not found in food. Instead, it is manufactured and stored in your liver after meals, to provide an energy reserve. After a large meal, your liver typically contains about 100 g of glycogen, which is sufficient to supply your body's energy needs for 10 hours or more.
References
- "Biochemistry"; Pamela C. Champe; 2005
- "Physiology"; Linda S. Costanzo; 2009
- Linus Pauling Institute: Micronutrient Information Center: Fiber
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