Best Way to Lose Fat | The Science of the Fat Burning Zone

January 18, 2023

Best Way to Lose Fat | The Science of the Fat Burning Zone

Topics of Interest

Topics Covered:

  • The most effective ways of burning fat (based on physiology and the data)
  • Confusions and myths around fat burning
  • Can you actually target certain areas of the body to pull fat from based on exercise choice

The Main Places Where You Find Fat

  • Fat is often referred to as adipose tissue
  • Places where fat can be found:
    • Deep into the skin (3rd layer down called the Hypodermis)
    • Surrounding organs
    • In the liver
    • Skeletal muscle

Burning Facts vs Burning Carbs

Muscles primarily consume energy through carbohydrates or fats

We want to find out what exercises burn more fats or carbohydrates.

For example, one the times that we burn the highest percentage or proportion of fats to carbs is at rest

Is There Actually a Fat Burning Zone?

Exercise intensity influecnese how our body consume fats compared to carbs. The chart below is from a male preparing for a marathon and so while the data won't be exactly the same between each person, the pattern generally is.

  • As you increase intensity (heart rate) the percentage of fat burned compared to carbohydrates is lower
  • HOWEVER, we need to look at the overall calories burned when increasing your intensity.

For example, in the chart above - If you're at a heartrate of 72 your total fat KCal burned per minute is 1.1. If you increase your heart rate to 127 the total fat KCal burned per minute is 4.7.

The "Fat" burning zone in the chart above is 138 (row 3).

The fat burning zone is dependent on many factors for a person though. Things such as:

  • Age,
  • health
  • medical issues
  • genetics
  • gender
  • fitness status

All influence where the fat burning zone would be for a person.

That being said, the fat burning zone for most people is around Zone 2 in the endurance world. Zone 2 training would be this level on intensity where you are working hard but you are still able to have a conversation with somebody (known as the "talk test").

Is this the most effective way of burning fat though?

  • NO

What Is The Most Effective Way Of Burning Fat?

The total amount of calories burned is the more important thing to focus on rather than focusing on the specific ratio of fats to carbs or finding that perfect fat burning zone.

If the goal is to just lose fat then the focus should just be on total caloric expenditure.


They took 2 groups and divided one group into a low intensity group that was doing Zone 2 training (fat burning zone) and then another group was in the high intensity group.

What they had to account for in those situations was the amount of time because it's common knowledge that spending 1/2 hour in the high intensity zone will burn more calories than being in a lower intensity zone.

The study therefore increased the amount of exercise time for the Zone 2 group to match the total calories burned by the higher intensity group.

At the end of the study they found that both groups lost fat or weight at the same rate (there was not a significant difference between the 2 groups).

So the study showed that the more important factor was total caloric expenditure rather than which zone you are in.

Pros/Cons of Higher Intensity Workouts


  • Some people just simply enjoy it more
  • It allows your burn calories in a shorter amount of time


  • If somebody is only focusing on high intensity training you risk overtraining and lose the benefits that come from Zone 2 training

Pros/Cons of Lower Intensity Workouts


  • Cardiovascular benefits
  • Increase in the number of capillaries that will grow and develop within muscle tissue
  • Muscle cells will increase the number of mitochondria
    • These mitochondria become really great at utilising fats for energy
  • Spending large amounts of time in Zone 2 will increase your % of fat consumed when exercising due to the mitochondria becoming more efficient. This can have a direct effect on endurance performance.

Our bodies can only store about 500g of carbs which is approx. 2000 calories (~8368 kilojoules). If we were just utilising carbs for an endurance race it would only last for about 1.5 hours.

Someone who is relatively fit can store upto 100,000 calories of fat (even more at higher body fat %). So if your body has spent a lot of time in Zone 2 due to training and you can mobilise fat it means you can spare some of those carbohydrates to utilise later on and last longer.

How Your Body Uses Fats After Exercise

Yes, technically there is a fat burning zone but it's not necessarily the most important thing to focus on if your main goal is losing fat. The main thing to focus on is the overall caloric expenditure (total amount of calories burned).

How does this work though if you're still burning more carbohydrates than fats?

  • Something else that also contributes to this idea of just focusing on the calories is something called "Excess Postexercise Oxygen Consumption"

Excess Postexercise Oxygen Consumption

  • It takes a little while for our bodies to "ramp" down after exercise (especially after a high intensity workout)
  • We have this "oxygen debt" that our bodies are trying to replenish all of the ATP that we utilised throughout the exercise
  • That replenishment is mostly coming from aerobic type mechanisms that utilise fats to replenish that ATP that we burned.

Can You Control Where You Pull Fat From?

Unfortunately not, we don't have any control of this as it's primarily decided by genetics


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