Is Fat Burning Zone a Myth?

As personal trainers, we get lots of questions about the "fat burning zone"; but, as Fitness Professionals, we need to make sure we are educated before we begin to educate our clients.  One myth that has been floating around for years is the "fat burning zone".  It was once believed that exercising at a lower intensity would burn more fat than exercising at a higher intensity.  This misinterpretation or myth spread after several studies concluded that high intensity exercise relied more on carbohydrates.  For example, walking burns 50% of its calories from fat and 50% from carbohydrates.  Moreover, running would only use 40% of its energy from fat while relying on 60% carbohydrates.

However, a closer look at the studies revealed that while a higher percentage of fat is used for low intensity exercise, there are more total calories and more total fat calories used for high intensity exercise.  This stands to reason as runners are normally less fat than walkers.

Also, exercising at a higher intensity induces a greater rate of "excess postexercise oxygen consumption".  That is, once you are done with your high intensity exercise, your body continues to consume oxygen and burn fat for up to 3 hours after exercise.  Furthermore, exercising at a higher intensity also improves your cardiovascular system.

In summary, while low intensity exercise is a great place to start for beginners, the best way to burn fat, lose weight, and improve your cardiovascular system is to increase the intensity of your exercise when you or your client are able to.  You can start by charting you or your client's exercise intensity and continue to increase intensity throughout your exercise plan.

Source: Gregory L. Welch, "Fat Burning Zone", 1998.