Ever heard people talk about the ‘fat burning’ zone before? Ever heard people say that if you walk you will burn more ‘fat’ than if you run? Sound too good to be true…. That’s because it is! This mythical ‘fat burning’ zone is inferring that exercising at a low heart rate (60-70% of max heart rate) will burn more fat than working at a high intensity.
During exercise we use a combination of fat, carbohydrates and protein to give us energy. Fats are a vast energy source as we have enough to last us around 5 days. We mainly use fats as a dominant fuel source at low intensities because they break down quite slowly. Carbohydrates (stored in the muscle and liver as glycogen) are used at higher intensities because their break down rate is faster. Protein provides a minimal contribute to energy during exercise.
So yes it is true that we use fats at low intensities and carbohydrates as high intensities, however when trying to burn fat it’s not what fuel we are using that’s important it’s the total amount of calories we burn that really matters. The higher the level of exercise intensity, the greater the amount of energy required to fuel the exercise. Therefore, high intensity exercise will burn a greater amount of total calories than lower intensity exercise, it is this total calorie burn that we should be most concerned about.
A study that compared a 20 minute jog compared to a 60 minute walk found we burn over double the amount of calories during the jog. See the results below:
Low Intensity Exercise
Total Calories Burned – 277
% Calorie Burn from Fats – 50%
Total Fat Calories Burnt – 138.5
High Intensity Exercise
80-85% MHR (Heart rate Max)
Total Calories Burned – 986
% Calorie Burn from Fats – 25%
Total Fat Calories Burnt – 246.5
Whilst the lower intensity exercise burns a greater percentage of fat, the total amount of fat burnt in the higher intensity exercise is greater due to the substantial increase in total calories burnt.
Despite running burning more fat than walking, it’s not for everyone! It is important that you slowly build up to running if you are not already a runner. So next time you go for a walk try incorporating some intensity, for example try jogging for 30 – 60 seconds every couple of minutes. Try extending the length of the jog every time so you can eventually build up to jogging for the entire duration.
Research shows that it is not what fuel you are burning, whether it’s fats or carbohydrates, but in fact the amount of calories you are burning. As we have learned lower intensity exercise does burn a greater amount of fat but higher intensity exercise burns more calories which is more important. In order to build up to being able to jog continuously or work up to these higher intensity forms of exercise it is however important to start small and work your way up.