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Fasted Training: Yay or Nay



The great debate on fasted training! Is it ‘better’ or ‘worse’?


As ever, context is everything. Inherently, it is neither better nor worse. It all depends on the context!


So let’s dive into some of the debates, pro’s, con’s and context …


Is it ‘better’ for weight loss?


Short answer: no!


When we eat carbs, all else being equal, our body will use the carbs to power our training session. This is because they are the energy source we can access fastest. So we are likely to burn more fats and less carbs in a fasted training session than a fuelled training session, simply because there are not so many carbs available.


This does NOT mean we lose more body fat.


Why? Because it is just a timing thing! Body weight is determined by total calories in versus calories out. If I train fasted I burn more fat. But then I eat and depending how many calories I eat I will replace that fat or not. If I train fuelled I burn some fat and carbs. Depending how many calories I ate I will either use all these or not. If calorie intake is equal overall in both cases, the net outcome for bodyweight is the same.


We could get into the weeds and actually argue that if we train fuelled we might actually burn more calories if it means we can push harder for longer in training … !


A related topic is that of ‘Train Low’ and fat adaptation. This is where we become better at using fats in exercise by doing selected sessions with low carbohydrate availability. This can have benefits for the competitive endurance athletes, because if we can spare carbs by using more fats, we can typically push harder for longer in a long event … as our carbs don’t run out as fast. Carbs running out are where we then ‘hit the wall’ and cannot maintain our pace any longer. However, fasted training is not necessarily ‘train low’. This is because if I ate a high carb meal before bed, although I am fasted, my carb levels may not be low enough to drive this adaptation! And – as above – being fat adapted it is NOT better for weight loss because burning fat does not mean losing fat … losing fat is determined by total calorie intake versus total calorie burn … not whether these calories came from carbs or fats.


Are you training first thing?


If first thing in the morning is the only time you can consistently train, and you want to maximise the sleep you get for recovery then rolling out of bed and straight to the gym may be the best way to support your fitness!


And you may not want to eat anywhere between bed and getting to the gym, because of the risk of sickness (or the other end!) and stomach cramps as you train at high intensity or for a long period whilst food is digesting in your stomach.


The reason this occurs is that your blood is diverted from your gut to your muscles to enable them to move at high intensity. And so your gut reduces or stops digesting your food … so it just sits there jiggling about, or flushes out one end or up the other!


Will your training session be as ‘good’?


If energy (and particularly carbs) are lower than they otherwise might be because you are training fasted, then maximal training intensity and duration may be reduced. And, with reduced energy to power workouts, the perceived effort of the workout may increase. This may be a con, as it may cause you to further slacken off the intensity because you feel tired. This might mean you avoid placing key performance sessions at times you will be training fasted.


Or, a potential workaround is to use a sports carb powder or gel that is fast digesting. This provides energy for the session without sitting in your gut for an extended period. If you are training for 60 mins anywhere between 30-60g carbs per hour, combined with 750-1000 ml fluid (if taking 60g) may do the trick.


Plus, consider your final meal the day before. If training fasted and you want to maximise output (i.e. high intensity for an extended period) from the workout, you want to ensure you have some carbs available in your system. Easy way to do this: make sure your final meal of the prior day is high carb, e.g. a bowl of pasta or perhaps a bowl of porridge pre bed!


On the flip side, training fasted where everything feels harder may have an upside. It can make you more comfortable with the uncomfortable, meaning you can push further into the pain cave at times you train fuelled!


Does is lead to muscle loss?


If you are training fasted, the body is likely to have less energy and more limited building blocks immediately available. This means it is in a greater ‘breakdown’ state during exercise than it otherwise might be. In other words we may see greater breakdown of things like muscle protein during the workout.


This is not necessarily going to have a long term negative effect … assuming you fuel effectively after. So to recover effectively, hitting up sufficient carbs and protein soon after the workout is vital. If you are on the go, a protein smoothie or handful of jerky and dried fruit can tide you over until you can have a full refuel!


So there you have it! Some context and things to consider when thinking about fuelling before training (or not!).




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