The Fat Burning Zone: What You Need to Know

Set foot in any gym or on any piece of cardiovascular equipment and you’ll find it impossible to miss the charts directing you to train in the enticingly sounding “fat-burning zone.” You’ve heard about it, but what exactly is the fat-burning zone?

To exercise in the “fat burning zone”, means to exercise at lower intensity for better fat burning. How does it work? When you exercise some of the calories you burn are carbs and some fat. As exercise intensity changes (i.e. how hard you exercise), there is a shift in how much fat versus carbs your body burns to fuel your workout. Research shows that at lower exercise intensities, your body’s preferred fuel of choice is fat. The lower the exercise intensity, the greater the proportion of fat used for energy; as exercise intensity increases you burn progressively more carbs and less fat.

Advocates of the fat-burning zone have misconstrued this research, believing it to mean lower intensity cardio burns more fat. They’ve confused proportions and total amounts. And they’re definitely not the same.

Proponents of the fat burning zone have taken burning a greater percentage of fat to mean burning a greater total amount of fat. But, percentages are not the same as absolute numbers. And that’s where the fat burning zone theory collapses.

A large percentage of little is still little. Would you prefer 20% of Oprah’s fortune (a lot) or 80% of mine (a little)? Exercising at low intensity may burn a greater proportion of fat, but it does not necessarily burn more fat.

Let’s compare walking versus running. Walking burns a greater percentage of fat, but burns fewer calories. Running burns a smaller percentage of fat, but burns way more calories overall. In the end you’ll burn more fat running, that you’ll do from walking.

Activity (60 min)% of fat burned
Total Calories BurnedCalories from Fat
Walking50%300 calories150 calories
Jogging40%600 calories240 calories

Basically, you’re not interested in percentages of fat burnt, you want to know the actual number of fat calories burnt. The percentage of fat the body burns changes with intensity, but so does the amount of calories you burn. The more intensely you exercise the more calories you burn.

Lounging on the sofa is a very low intensity effort and burns the greatest percentage of fat possible, but that’s not going to help you lose weight, is it? You’re barely burning calories. Maximum fat burning, but minimum calorie burning. Remember, a large slice of little is still little.

Fat Burning Zone: Is it worth it?

You want to burn the greatest total amount of fat, not the greatest percentage of fat. Exercising at high intensity burns a lot of calories; so much more, that in the end, you almost certainly torch more total fat calories and experience greater fat loss.

And to tell you the truth, all this is talk about ratios, carbs and fat is just splitting hairs. In practical terms these fat/ carb ratios don’t make a big difference when it comes to losing weight and reducing body fat. If your goal is weight loss, calories are calories – whether carbs or fat. What really matters is how many calories you burn, not what you burn.

Does this mean you shouldn’t exercise at low intensity? Absolutely not. In fact, less intense, longer workouts (LSD) have their place in every workout schedule and have many advantages. But, what you must not do is fall into the fat burning zone trap by planning an entire exercise strategy around low intensity exercise.

So what’s best way to lose weight?

  • If you’re a beginner low to moderate intensity is a great way to start.
  • If you’re more fit and your goal is to lose weight, exercising at a higher intensity 2-3 times a week will get you there faster.
  • Mix up different types of cardiovascular training for maximum results. If you want to exercise more than 3 times a week, add in some lower intensity workout sessions to avoid overtraining, burnout and injury.
  • Alternate bursts of high and low intensity (interval training), and try adding short spurts of all-out efforts (high intensity interval training), to burn a greater number of total calories during your workout and to keep your metabolism elevated for hours after your workout. This will ultimately result in more fat loss from exercise.

2 sources

  1. Achten J, Jeukendrup AE. Relation between plasma lactate concentration and fat oxidation rates over a wide range of exercise intensities. Int J Sports Med. 2004;25(1):32-7.
  2. Phelain JF, Reinke E, Harris MA, Melby CL. Postexercise energy expenditure and substrate oxidation in young women resulting from exercise bouts of different intensity. J Am Coll Nutr. 1997;16(2):140-6.

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