Fasted cardio v standard cardio – which is best?


A popular debate, and one that I have flip flopped on when it comes to fat loss is ‘fasted cardio’ vs ‘standard cardio’ and which is best. Everyone is looking for that magic bullet, that differentiator that could be the missing link in why they’re not losing weight. Has there been something so small all this time that has stopped me from making the breakthrough I’ve been searching for?

What is fasted cardio?

‘Fasted’ cardio is the practice of doing cardio on an empty stomach or in a ‘fasted’ state.  When you traditionally train, your body will go to it’s glycogen stores to utilise it as fuel.  Glycogen is our primary energy source and fuelled by carbohydrates.  This is typically why you will see endurance athletes or footballers drinking sports drinks during competition to replenish their glycogen and give themselves as much energy as possible.

A recent concern that has emerged in the fitness industry is that if you train fully fed you’re simply burning calories from the carbohydrates in your system which will then be refuelled after food, meaning you burn no fat.  The theory goes on to suggest that ‘fasted’ cardio is the optimum way to burn fat.

A fast can be anything over 8 hours of not eating.  This leaves your body with depleted levels of glycogen (commonly sourced from carbohydrates) to use for energy.  In this instance the body has to take energy from somewhere and will therefore start to ‘burn’ fat as it’s new primary source of fuel, doesn’t that sounds unbelievable?  I can actually burn fat as fuel?  That is fantastic!  Unfortunately it’s not quite as straight forward as this…let’s look into why.

‘Calories in’ versus ‘Calories out’ (CICO)

It can be easy for people to hear ‘new wave’ ideas that could be the single reason why they’ve been going wrong the entire time but in reality is not the answer. When training, whether fasted or fed you are exerting more energy from the body than if you didn’t train.  Obviously the more rigorous and longer the session the increased energy expenditure.  This will then play into your TDEE (Total daily energy expenditure) alongside how far you’ve walked, cycled, swam or even fidgeted that day to give a final figure.  This figure then needs to be taken off the amount of energy you’ve inputted that day through food & drink – calories.  This gives a very simple equation of:

Calories in – Calories Out = body / weight maintenance

If the equation balances to 0 you will maintain your weight.  If you’ve consumed more than you’ve exerted you’ll begin to store fat and if you’ve exerted more than you’ve put in you will lose weight!  When this is applied consistently over a longer period of time you will begin to see results.

Now, with the above ‘fasted’ approach there can be benefits.  For example, you can get the benefit of making the body efficient at using fat as a fuel source and improving the body’s ability to perform for longer periods with less glycogen, such as endurance athletes.  However, despite what the ‘bros’ say you don’t get a magic overlay to the equation through training fasted.

For example, if I were to train fasted in the morning and burn through 500 calories and then for the rest of the day my body burns through say 2000 calories my total daily energy expenditure (TDEE) is 2500 calories for that day.  If I then eat / drink 3000 calories (easily done) then I have a net overlay of 500 calories – in this instance I am storing body fat rather than losing it!  Doesn’t the magic of the fasted cardio give me any added benefits?  Not in this context.

What does this lead to?

Articles that glamorise ‘magic formulas’ to lose body fat can be dangerous and misleading.  Individuals are left thinking if they follow that very specific formula that they’re going to make a breakthrough but are left unaware that it is other areas of their lifestyle that could be letting them down.  It can also be that some people react quite negatively to training fasted therefore put themselves through the pain barrier for no additional return.  People also love a ‘scientific’ discovery that sounds like a golden nugget.

So what should I do then?

Essentially, it’s about finding the system that works for you.  I personally like to train fasted as I train first thing in the morning so it helps me contain my calories when in a deficit within a narrower window of the day.  This helps me to control hunger and means I have more calories in a smaller period of time.  I wake up at 6am and train at 7am.  If I eat during this period it just gives me less calories to play with between 7am and 11pm.  By delaying my first meal until 9-10am I can far easier control cravings and back weight a lot of my calories to the evening when I like to treat myself – This is what works for me.  I am under no illusions that this is simply a timing strategy for me rather than an extra ‘fat melting’ system.

Does this mean Intermittent Fasting (IF) doesn’t work?

I am not saying intermittent fasting doesn’t work – but what I am saying is that fasting doesn’t give you a magic formula that ‘melts’ fat.  Lots of people find success with IF over a short period of time given the diet, which only allows you to eat within a specified window (say 12pm – 6pm), normally manages to cut calories as people end up missing a meal or two (breakfast or evening snack).  This is essentially a more complex and indirect way of getting you into a calorie deficit, and potentially quite anti-social.  However, individuals who then eat 2 days worth of food within their allotted window tend not to see results – it comes back to that same old argument of calories in vs calories out.

In summary

If you’re controlling your diet, tracking your macros and hitting a calorie deficit consistently you will begin to lose weight over a period of time.  Chose whether you want to workout ‘fasted’ or ‘fed’ but know that it’s all about finding a methodology which works for you as long as you’re in that all important deficit!  To find out more about the my personal training and nutrition plans click here.

All views are my own.