Fat Burning: The truth about HIIT

Is HIIT the magic bullet for fat burning?

High Intensity Interval Training (or HIIT) is often cited as a magic bullet to increase ‘fat burning’ while reducing body weight and improving overall health. There is little doubt that HIIT, or any kind of exercise for that matter, improves health contributes to weight management and fat loss. Yet HIIT’s ability to stimulate fat burning during exercise itself is somewhere in the region of zero! As humans increase the exercise intensity from low to high, there is a gradual (sometimes rapid) increase in the amount of carbohydrates combined with a substantial decrease in fats used to produce energy in muscle. This is highlighted in the figures below. The key point is that HIIT is not fat burning! It is however energy sapping and if combined with the correct life-style and nutritional intake, it can help reduce fat mass while encouraging gains in lean muscle mass when combined with traditional resistance exercise.

Fat is NOT burnt during HIIT because…

1. Fast-twitch fibre recruitment

2. Accelerated glucose requirements

3. Reduced fat breakdown

4. Reduced fat deliver to muscle

HIIT Podcast

A quick Google search using “HIIT & Fat Burning’ revealed 79,800,000 results in 0.83 sec. The first video to appear is of Joe Wicks tells us he has a 15 minute “Fat Burning HIIT workout”. There is no shortage of celebrities selling fat burning exercise sessions but we should all be clear, these exercise’s themselves do NOT burn fat during the session. They may very well help reduce body mass, and increase lean mass in the hours afterwards, but HIIT does not burn fat during exercise.

If you want to hear more information, have a listen to our Podcast on this topic with Dr Gibala and feel free to read our recent paper on the topic from Dr Mackenzie’s lab here.