Is the Fat Burning Zone the Best Way to Lose Weight?

The wellness industry is full of buzzwords that sound flashy and scientific, but are more often than not designed to sell products and services rather than convey useful information. One that I most often hear being misused or misunderstood is ‘Fat Burning Zone’. Anyone trying to lose weight might hear reference to the ‘fat burning zone’ might reasonably think that being in the ‘fat burning zone’ is the best way to lose fat. Let’s take a look at what ‘fat burning zone’ actually means and why it’s neither the best way nor only way to lose weight.

What is the ‘Fat Burning Zone’?

During cardiovascular training we (somewhat arbitrarily) divide the intensity of the training into 5 zones, ranging from maximum heart rate - zone 5, to zone 1, about 50% of your maximum heart rate. When you hear someone talking about your ‘fat burning zone’ typically they are referring to ‘zone 2’ or working at 60-70% of your maximum heart rate.

The problem

The problem with the ‘fat burning zone’ is that it is usually presented without any kind of explanation or context leading to the myth that you need to exercise at 60-70% of your maximum heart rate to lose weight. This is just not true. The body uses both fat and carbs for fuel and, depending on the intensity of the activity, will use a greater portion of one or the other.

Crossover Concept: During lower intensity activities a greater portion of the energy burned is fat. During higher intensity, a greater portion is carbohydrates. But it's a gradient, not a switch.

"Fat Burning Zone"

Suppose you are planning a 30 minute run in zone 2. At that pace you might complete 2 miles and burn 200 calories. We know that in zone 2 about 70% of the energy burned comes from fat.

70% of 200kcal is 140kcals of fat in 30 minutes. 

Higher Intensity Training

If instead you decide to work at a zone 3 pace (70-80% of your max heart rate) you might complete 3 miles and burn 300kcal. During zone 3 you might only be burning 50% of your calories from fat.

50% of 300kcal is 150kcal of fat.

The Bottom Line

What if instead you decide to walk three miles instead of running? You’re still burning about the same number of total calories. At a lower intensity the same distance will take you longer, but an even higher percentage of those calories will be calories from fat. There is a lot of variability and this example is somewhat contrived, but it highlights an important point regarding the percentage fat burned vs total calories burned.

‘Fat burning zone’ is a real thing. But ‘fat burning zone’ is most often applied to weight loss and it doesn’t take into account that total calories burned is more important than the percentage of calories burned made up of fat. What the fat burning zone actually tells us is how to burn 300 calories as quickly as possible while making sure the greatest percentage of those calories are from fat. It can be a useful tool and is great for improving cardiovascular endurance, but it shouldn’t be the guiding principle of your weight loss program.

Benefits of the 'Fat Burning Zone'

None of this is to suggest that you shouldn’t include zone two training as part of your schedule. Sustained exercise at 60-70% of your maximum heart rate improves cardiovascular endurance, builds denser capillaries and even increases the number of mitochondria in the cells. If you’re regularly doing vinyasa type yoga classes you’re probably already training in zone 2. The next time a teacher or coach or trainer tells you that you’re in your fat-burning zone, you’ll know exactly how much importance to give it.