Exercise Timing & Fat Loss


by Skye Swaney

Do you force your tired body out of bed in the morning and drag yourself through a workout in the belief that if you exercise on an empty stomach you’ll burn more fat?

The fasted cardio craze

In the last few years the popularity of ‘fasted cardio’ – exercising in the morning on an empty stomach – has moved beyond the confines of body builders and into the realm of the regular gym goer. And no wonder, who wouldn’t sign up for the promise of increased fat burning for the same amount of effort? But before you lay out your gym gear and set your alarm or 5am, let’s look at whether it actually makes a difference?

The theory is that if you exercise first thing in the morning in a fasted state, there is very little carbohydrate (glucose) available and therefore fat is burned instead to fuel the exercise. On the surface this makes sense. But unfortunately for us, our bodies aren’t so easy to manipulate.

What the science says

Numerous studies have investigated this controversial topic, comparing the results over time of exercise in the fasted state versus exercise after eating. In the majority of studies, no changes in body composition were found when overall exercise amount and energy intake were the same.

It is true that you will burn a greater percentage of fat in a fasted state, but this doesn’t actually mean that you’re burning more fat in total over the course of the day. The reality is that if you burn more fat while exercising but still eat the same amount overall, you’ll simply end up burning more carbohydrates later on in the day. So whether you eat breakfast before you exercise or afterwards, the net result is the same in terms of fat burned.

Fasted exercise = lower intensity exercise

Then there is the issue of exercise intensity. Ever tried to go for a run after fasting for 12 hours? Chances are it wasn’t you best performance – and it probably wasn’t particularly enjoyable either. Exercising on an empty stomach meas that there is less energy available for the body to use, which results in lower intensity exercise. Unfortunately, lower intensity exercise means fewer kilojoules burned, which means less fat loss. So, contrary to the fasted cardio theory, eating before you exercise can in fact increase fat loss as you’ll be able to exercise at a higher intensity and burn more kilojoules.

What really counts

Ultimately, what is most important is what’s going to work for you in the long term/ Dubious fat loss benefits aside, many people simply find that exercising first thing in the morning means that they are more likely to do it. For many of us, the risk of making up excuses or getting side tracked can increase exponentially as the day goes on, so getting it done first thing in the morning definitely has its benefits.

On the other hand, mornings just don’t work for some people. If you’re one of these people, there’s absolutely nothing wrong with going for afternoon or evening workouts when you feel more energised. The bottom line is that the best time of day to exercise is the time that suits you.


This article was originally published on Dr. Joanna McMillan’s site.

Dr Joanna McMillan

Joanna has a PhD in Nutritional Science, is one of Australia's best known health experts and founder of Get Lean. She is also the author of several books, has a weekly column in Sunday Life and writes for several magazines and online blogs. She is also a proud ambassador for Diabetes Australia, The Skin & Cancer Foundation, FoodBank NSW/ACT & Muscular Dystrophy.

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