Your Fat-Burning Zone and Weight Loss

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If you exercise because you want to lose weight, you've probably heard or been told that for best results you should work in your "fat-burning zone." (Sounds enticing, right? Who doesn't want to burn more fat?) But the term "fat-burning zone" is misleading and tells only part of the working-out-for-weight-loss story. 

Target Heart Rate Zones

When it comes to exercise, particularly cardio exercise, there are different​ heart-rate zones that equate to different levels of intensity. These levels actually determine which energy systems your body uses during exercise, and that often directly affects how many calories you burn.

There are four different training zones and each is a percentage of your maximum heart rate (MHR), the maximum number of times your heart can beat in a minute:

  • Low-intensity, also known as the "fat-burning zone," is 50% to 70% of your MHR. It's usually considered light cardio or a warm-up level.
  • Moderate-intensity is 70% to 80% of your MHR. At this level, you'll be working out but still be able to talk. 
  • High-intensity is 80% to 90% of your MHR. This usually puts you well out of your comfort zone and pushes you to your anaerobic threshold, which is when your cardiovascular system can't deliver oxygen to your muscles fast enough. 
  • Maximum effort is 90% to 100% of your MHR, something that even the most highly trained athletes can't maintain for more than a few minutes.  

The Truth About Your Fat-Burning Zone

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 stored fat (versus carbs) as its primary fuel source when you work at a lower intensity compared to a higher intensity.

Some people have translated this to mean that you actually burn more fat when you work at a lower intensity, but that's a bit of a misconception. In reality, picking up the pace will torch more total calories—and ultimately more fat—in less time. And it's the number of calories you burn overall that leads to the most weight (and fat) loss.

To give you an example, the chart below details both the total calories and the fat calories expended by a 130-pound woman during cardio exercise.

  Low Intensity
(60% to 65% MHR)
High Intensity
(80% to 85% MHR)
Total calories burned per minute 4.86 6.86
Fat calories burned per minute 2.43 2.7
Total calories burned in 30 minutes 146 206
Total fat calories burned in 30 minutes 73 82
Percentage of fat calories burned 50% 39.85%

As you'll see, the woman burns more total calories and more fat calories when working out at a higher intensity.

While lower-intensity workouts are great for beginners and for building endurance, you need to work harder during some workouts if you really want to burn fat and lose weight.

The Importance of Low-Intensity Exercise

Now, this isn't to say that low-intensity exercise doesn't have its place, especially if you're just starting out and can't sustain a faster pace. If you go slower, you may be able to exercise a lot longer, so you'll end up burning more calories and fat that way. 

Even for more advanced exercisers, endurance workouts should be a staple of a complete fitness program along with short, high-intensity interval workouts. Interval training where you alternate high-intensity exercise with low-intensity recovery periods is proven to increase fitness and burn more calories than steady-state cardio.

Structuring Your Cardio Workouts

If you want to lose weight, a general cardio schedule would include workouts at a variety of intensities within your target heart rate zone. For instance, if you're doing five cardio workouts a week, you might have one high-intensity workout, one lower-intensity workout, and three somewhere in the middle.

Sample Cardio Program for Beginners

A beginner cardio program lets you slowly build endurance while getting you a bit out of your comfort zone. That way, you don't have to spend an entire workout miserable, yet you'll still challenge yourself, which will burn more calories.

Below is a sample program that will help get you started. 

Day Workout Intensity Time
Monday Beginner-Interval Workout Level 1 Up to 21 minutes
Tuesday Low-Intensity Walking 10 to 20 minutes
Wednesday Rest  
Thursday Cardio-Endurance Workout Up to 35 minutes
Friday Rest  
Saturday Beginner Interval Workout Level 2 Up to 25 minutes
Sunday Low-Intensity Walking 10 to 20 minutes

The key is to start with what you can handle and slowly build from there. 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 manage on a regular basis.

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Article Sources
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  1. Carey DG. Quantifying differences in the "fat burning" zone and the aerobic zone: Implications for training. J Strength Cond Res. 2009;23(7):2090-5. doi:10.1519/JSC.0b013e3181bac5c5

  2. American Council on Exercise. I’ve Heard That Performing Aerobic Workouts at a Low Intensity Is Best for Losing Body Fat–Is That True?.

  3. U.S. Department of Health and Human Services. Physical Activity Guidelines for Americans, 2nd edition. 

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