Carbohydrates Burn at What Rate in the Body?

At any given moment your body is using a combination of carbohydrates, fat and protein for energy. How much of each energy source is being used depends primarily on your activity level. Lower-intensity activities rely heavily on fats to supply energy while higher intensities require more carbohydrates. The respiratory quotient will allow you to determine the relative percentage of each nutrient being utilized during any activity.

Exercise Intensity and Carbohydrate Utilization

The predominant factor determining how much carbohydrate your body uses is exercise intensity. At rest, the body primarily uses fat to supply needed energy. As intensity increases, the body relies less on fat and more on carbohydrates. At very high intensities, carbohydrates are the primary source of energy in the body. It takes more time for the body to convert fat into usable energy than carbohydrates. When energy is needed quickly, as in intense exercise, the body prefers carbohydrates for fuel.

Respiratory Quotient

Carbohydrates Burned During Exercises

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The respiratory quotient is the ratio of carbon dioxide produced by the body to oxygen consumed when breaking down carbohydrates, fats and protein for energy. An RQ of 1.0 would represent the body using 100 percent carbohydrates for energy. An RQ of 0.70 represents total fat utilization, while 0.82 represents total protein use. Typically, the body uses a blend of nutrients for energy and the RQ value ranges somewhere between 0.70 and 1.0.

Respiratory Quotient and Exercise Intensity

Walking at a moderate pace has a respiratory quotient of 0.85, meaning you'd burn approximately 50 percent fat and 50 percent carbohydrate. Walking for one hour burns approximately 254 calories, or 127 calories of carbohydrates. Compare that to running, with a respiratory quotient of 0.89. At that RQ, energy comes from approximately 64 percent carbohydrate and 36 percent fat. In one hour you would burn 572 calories, 366 calories from carbohydrates.

Carbohydrates to Fuel Your Workout

The Digestive & Circulatory Systems Converting Food Into Energy

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Consuming enough carbohydrates in your diet to supply adequate energy is an important consideration in your diet and exercise program. Failing to eat enough carbohydrates forces your body to rely on protein for energy and that protein comes from the breakdown of your lean muscle. Eating a healthy diet will ensure adequate amounts of each nutrient are available. Always consult with your physician before beginning a diet or exercise program.