How Many Minutes of Exercise Till the Body Burns Stored Fat?

Understanding how the body uses energy for exercise aids in effective training. For fat burning, increase both intensity and duration. It takes several minutes for the body to use fat storage for energy, so a longer workout results in more fat burned. More calories are burned, including fat calories, during higher-intensity workouts. Higher-intensity and longer-duration workouts are the keys to burning stored fat.

  1. Intensity and Duration

    • Intensity and duration are the key factors in burning fat during exercise.

      Intensity and duration of exercise are the key factors regulating the source of fuel the body uses during exercise. Short-duration exercises, such as sprints, will predominantly use stored ATP and phosphocreatine. Exercises between one and two minutes predominantly use anaerobic glycolysis for energy. Increasing duration to several minutes causes stored carbohydrates and fats to become the primary energy source. Increase duration of exercise to burn stored fat.

    Energy During Exercise

    • The body turns to fat for its primary energy source after 90 minutes.

      The amount of energy available from stored ATP and phosphocreatine is easily accessible but very small, making it the perfect energy source for sprints and other exercises of short duration. The amount of energy from stored carbohydrates is larger, but it is still limited. However, the amount of available fuel from fats is essentially unlimited. After 90 minutes of exercise, the majority of carbohydrate stores are depleted, turning the body's primary energy source to fats.

    Estimating Fuel Contribution

    • The respiratory quotient (RQ) is a calculated number that can determine the relative contribution of fats and carbohydrates as fuel sources. A respiratory quotient measurement of 1.0 indicates that 100 percent of the energy is fueled by carbohydrates. A respiratory quotient of 0.7 indicates that fat is supplying 100 percent of the fuel for exercise. A measurement in between 0.7 and 1.0 indicates a combination of carbohydrates and fats fueling the exercise. Tables can be found online that show exactly how the mixture of fuel changes depending on the RQ.

    The Myth of the Fat-Burning Zone

    • A higher intensity will burn more calories, including calories from fat.

      Understandably, some people believe low-intensity exercise burns more fat because it does not require the body to energize quickly from carbohydrates. However, though a lower-intensity workout does decrease RQ and increase calories derived from fats, a higher-intensity workout raises the total caloric expenditure, including from fats. For example, a woman walking for 20 minutes at 3 mph expends 4.8 calories per minute, with 3.2 coming from fat. A woman doubling the intensity to 6 mph for 20 minutes would result in 9.75 calories expended per minute, with 4.48 from fat. For the full 20 minutes, 64 calories were metabolized from fat while walking and 90 calories while jogging. A slightly higher intensity nearly doubled the caloric expenditure from fat, despite the increased reliance on carbohydrates as the primary fuel source.