Fitness Facts: Fasted Cardio

So fasted cardio……..This form of workout has gained popularity due to its purported increases in fat burning but were you aware that there are some significant caveats and situations where we can actually be causing the opposite effect by exercising in this way?

As part of a new series of posts on my social media channels (find me on Instagram and Facebook) I have decided to share two specific research based de-mystifying posts a week – Tuesdays will be related to nutrition, naturopathy and general health, and Fridays to fitness and lifestyle practises. I am always happy to take suggestions for topics to cover so feel free to comment below or directly message me if you have a burning question or are confused about anything in particular 🙂 .


So diving into this topic –  the research behind improved fat metabolism is relatively shaky, and in fact many studies have found no difference in the quantity of fat burned when compared to exercise performed after a meal. There have also been a number of papers published to indicate you actual double the protein you burn (AKA your hard earned muscle mass!) when you workout on an empty stomach as any fat liberated cannot be broken down fast enough for you to use for energy. Not ideal by any means!

From a functional medicine perspective fasted cardio/workouts in general may also stimulate the other systems of your body in a negative way as they spark your ‘fight or flight response’. In a very summarised way (find more information on this topic here) if this happens repetitively we will begin to see raised cortisol levels which will actually cause you to hold more fat as a protective mechanism……..oh dear. In women this can be doubly concerning as long term fight or flight will seriously affect hormone levels – many female gym bunnies finding their periods become irregular or disappear altogether. And actually men should not discount this effect either, many may experience a loss of libido when performing regular intense or endurance exercise.

So my advice?

If you enjoy fasted cardio that’s fine, it will make many people feel good due to that sparking of our stress hormones (which we will know more familiarly as an adrenaline rush) but as a blanket statement I wouldn’t advise this form of workout more than once a week.

Also if you currently experience any hormonal irregularities, PMS, anxious feelings, mood swings, poor immunity, fatigue, or sleep disturbances I would strongly urge you not to do fasted cardio at all as all of those things say to me that your body is already struggling somewhere. Instead you would be much better served by a more calming practise such as yoga or pilates  which will not only help you build lean muscle mass but also lower those cortisol levels.

I hope that un-muddies this topic for you and as always please do not hesitate to come to me with any additional questions.

With health wishes,

Phoebe x

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