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What Is the Basic Function of Carbohydrates?

by James Connell

About James Connell

James Connell is a nutritionist who has been writing about his field since 2003. He has authored material for Quest Vitamins and various health publications, now advising clients at his private clinic in Wales. Connell has a Bachelor of Science in applied human nutrition from the University of Wales.


Carbohydrates -- chains of sugars that differ in their length and complexity -- serve as your primary source of energy. After you eat carbohydrates, energy is released from these sugar chains to immediately fuel your metabolism. Your body also has the ability to store carbohydrates for use when energy from food is not available.

Metabolic Fuel

Carbohydrates provide around four calories of energy per gram. During the three or four hours that follow a meal, the enzymes of your digestive system break down carbohydrates into glucose, which your body then uses for energy. The rate at which carbohydrates release energy depends on their structure. Complex carbohydrates, such as those found in pasta, release energy more slowly than simple sugars, such as table sugar. Carbohydrates contribute to your energy supply both at rest and during exercise, but they are especially important during anaerobic activities, because they can fuel exercise even without oxygen.

Energy Store

When your intake of carbohydrates is greater than what you require to meet your demand for energy, the excess does not go to waste. Glucose from digested carbohydrate that is not immediately required is converted to a substance called glycogen, which is similar to starch, and is stored in your muscles and liver. This storage form of carbohydrate is then mobilized during the fasting state, when levels of glucose in the blood begin to decline.

Brain and Red Blood Cell Function

Although protein, fat and alcohol also provide your body with energy, your red blood cells and your brain rely entirely on glucose as their source of energy. After prolonged starvation, your brain can begin to use ketones for energy, but under normal circumstances it exclusively uses glucose as its fuel source. Without adequate glucose, your brain cannot function properly, which accounts for the negative effects a low blood-sugar level has on mood and ability to concentrate.

Macronutrient Interactions

When adequate carbohydrates, either from food or glycogen stores, are unavailable to meet your need for metabolic fuel, your body will begin to break down protein as an energy source. This condition is especially undesirable if you are an athlete or someone who is trying to build muscle through resistance training, because it will deplete your muscle tissue. Ensuring an adequate supply of carbohydrates in your diet will spare dietary protein for the growth and repair of muscle tissues. Conversely, if you consume so many carbohydrate that you saturate your glycogen stores and consume many calories, the excess carbs will be converted to and stored as fat.

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This article reflects the views of the writer and does not necessarily reflect the views of Jillian Michaels or JillianMichaels.com.