Because carbohydrates are your body’s primary source of fuel, you burn them daily. Within your bloodstream, carbs are available as glucose, or blood sugar. Your muscles and liver store a form of carbohydrates known as glycogen. The chemical bonds of carbohydrates require less energy to break down than those of fats or proteins.

Fuel Factory

All of the tissues in your body including your brain and other organ systems depend on glucose in order to function optimally. Every motion your muscles generate requires energy. The primary source of your body’s energy comes from adenosine triphosphate -- ATP -- which is formed through several different processes when carbohydrates are broken down and converted. Eating too few carbohydrates may leave you feeling tired because your body has less access to an immediate fuel source and has to work harder to convert other fuel sources into ATP.

Complex vs. Simple

Carbohydrates are largely divided into two main types: simple and complex. Complex carbs are found in whole grains, vegetables, fruits, nuts and seeds. These carb sources must be broken down before they can be converted to glucose and later into ATP. Simple carbs, also called simple sugars, are often found in sugary beverages, candy and products that use white flour. Simple carbs can be quickly broken down into glucose. Because they can quickly enter the bloodstream, simple carbs, if not immediately used to fuel activity, can be stored as fat.