The Truth About the Fat Burning Zone

Woman walking on the beach
Woman walking on the beach. Alistair Berg/Getty Images

Do you exercise because you want to lose weight? If so, you've probably heard, or been told, that for best weight loss results you should work in your "fat burning zone. But what is the fat burning zone and does it really work? How hard should you really work during exercise?

What Is the Fat Burning Zone?

When it comes to exercise, particularly cardio exercise, there are different heart rate zones that equate to different levels of intensity.

These different levels of intensity actually determine which energy systems your body uses during exercise and that often directly affects how many calories you burn.

We usually look at four different heart rate zones when it comes to exercise, a percentage of your maximum heart rate (MHR):

  • Low intensity, also known as the 'fat burning zone' is 60% to 70% of your maximum heart rate and usually considered light cardio or warm-up level.
  • Moderate intensity is 70% to 80% of your maximum heart rate or a level at which you're working but you can still talk.
  • High intensity exercise is 80% to 90% of your maximum heart rate, putting you well out of your comfort zone and pushing your anaerobic threshold.
  • Maximum effort is 90% to 100% of your maximum heart rate, something for very advanced exercisers, athletes, and professionals.

From these numbers, you can see that the fat burning zone is the lowest intensity.

So, why is it called the fat burning zone? Because the body relies on more fat for fuel when you work at a lower intensity.

Some people have translated this to mean that we actually burn more fat when we work at a lower intensity, but that's a bit of a misconception. While lower intensity workouts are great for beginners and for great for building endurance, you need to work harder for some of those workouts if you really want to lose weight.

The Truth About Your Fat Burning Zone

The thing is, the body does burn a higher percentage of calories from fat in the fat burning zone or at lower intensities.

However, at higher intensities (70-90% of your maximum heart rate), you burn a greater number of overall calories.

It's the number of calories you burn that leads to the most weight loss and you just won't burn as many when you work at a low intensity all the time.

The chart below details the fat calories expended by a 130-pound woman during cardio exercise.

 Low Intensity - 60-65% MHRHigh Intensity - 80-85% MHR
Total Calories expended per min.4.866.86
Fat Calories expended per min.2.432.7
Total Calories expended in 30 min.146206
Total Fat calories expended in 30 min.7382
Percentage of fat calories burned50%39.85%

Source: From The 24/5 Complete Personal Training Manual, 24 Hour Fitness, 2000

In this example, the woman burns more total calories and more fat calories at a higher intensity.

This isn't to say that low-intensity exercise doesn't have its place. In fact, endurance workouts should be a staple of a complete fitness program along with shorter, higher intensity workouts or interval workouts, which are a great way to burn calories and build endurance.

To figure out your own target heart rate zone, you can use  these detailed steps for figuring out your own levels of intensity.

Structuring Your Cardio Workouts

So, if you want to lose weight, what should a cardio program look like?

A general schedule would include workouts at a variety of intensities within your target heart rate zone.  If you're doing 5 cardio workouts a week, you might have one high intensity workout, one lower intensity workout and then two somewhere in the middle.

Sample Cardio Workout Program for Beginners

Let's say you're a beginner and you're trying to figure out just how to put together a cardio program that lets you slowly build endurance while getting you a little out of your comfort zone, which will help burn more calories.

Where do you start? You begin by focusing on more moderate interval training - Practicing getting just out of your comfort zone a little at a time so that you don't have to spend an entire workout miserable, yet you still challenge yourself.

Below is a sample program with about 3 days of cardio and 2 days of walking.  Another great option is to get a pedometer or activity tracker to keep track of your steps on a daily basis.

DayWorkout/IntensityLength
MondayBeginner Interval WorkoutUp to 21 Minutes
TuesdayLow-Intensity Walking10-20 Minutes
WednesdayRest 
ThursdayCardio Endurance WorkoutUp to 35 Minutes
FridayRest 
SaturdayInterval Training Level 2Up to 25 Minutes
SundayLow-Intensity Walking10-20 Minutes

 

The key is to start with what you can handle and slowly build from there. And, if you're just getting started, don't worry too much about how hard you're working. Focus more on making exercise a habit you can keep up with on a regular basis.

Source:

Carey DG. Quantifying Differences in the “Fat Burning” Zone and the Aerobic Zone: Implications For Training. Journal of Strength and Conditioning Research. 2011;25(8):1-1. doi:10.1519/jsc.0b013e3181f7c424.

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