The so-called fat burning zone occurs when exercise is primarily fueled by body fat. It’s a belief that is based in exercise physiology, but one that is now considered misleading because it overlooks a key factor: total calories burned.

To understand how low and high-intensity exercise influences weight loss, it helps to first understand how the body uses fuel during exercise.

Exercise is fueled by a mix of fat and carbohydrates. Exercise intensity changes the amount of fat and carbohydrate used by the body. When exercise intensity is low, the body uses a greater percentage of fat to fuel muscles. As intensity increases, the body increases its use of carbohydrates.

While the calories burned during low-intensity exercise are primarily sourced from body fat, higher intensity exercise can burn more stored fat in the same amount of time because the total amount of calories burned is greater. The table below provides an example.

*Energy expenditure (calories) based on a 45-minute workout with constant intensity

Low-intensity exercise has its place in your workout plan, especially if you are a beginner. But don't hold back your intensity level because you think a lower intensity workout will create a magic fat-burning zone. As you become fit, start incorporating high-intensity intervals into your workouts to maximize your fitness and weight loss.

Lori Rice, M.S., is a nutritional scientist and author with a passion for healthy cooking, exercise physiology, and food photography.