Should I be training fasted?

‘Should I be training fasted?’ is a common question I get from clients who are athletes or recreationally active. And my answer is always ‘Well, it depends’.

When I’m asked this, I always like to first understand their reasoning. And as you’ve probably guessed, most of them say it’s because they want to lose some extra body fat. Unfortunately, it’s not that simple.

Training fasted means training in a non-fed state, i.e. with reduced energy availability. Normally, this is done after waking up from an overnight fast (before breakfast). When you exercise in the fasted state, the body increases its use of fat as fuel while carbohydrate use decreases because glycogen availability is reduced. And this is exactly where most people get it wrong…using more fat as fuel does NOT equate to losing body fat! A negative energy balance needs to be maintained for a prolonged period for there to be any effective body fat loss. If you train fasted and then don’t really care about what you eat for the rest of the day, that’s not going to help much at all.

Some research suggests that this selective fat use from fasted training can extend over 24 hours and is independent of energy balance. So, in theory, fasted training combined with consuming less calories than needed should help to accelerate body fat loss, right? Well, it’s not that straightforward. Why? Because we’re complex human beings, not machines. And the current evidence supports this given that the findings are mixed and inconclusive.

One reason why I wouldn’t recommend training in the fasted state every day, purely for fat loss, is because this actually stresses the body on top of the exercise, increasing the risk of immunodepression and muscle mass loss. Plus, if you consistently train in the fasted state, you risk underperforming because your training intensity might be compromised.

While I understand that training fasted might help magnify the training stimulus by promoting ‘metabolic flexibility’, i.e. the flexibility of the body to tap into carbohydrate or fat stores when needed, these fasted sessions should be carefully planned so training intensity isn’t compromised. Therefore, I always suggest that if you’re going to train fasted, do it on your ‘easier’ training sessions. This will also put less stress on the body and reduce the risk of immunodepression and muscle mass loss.

For the purpose of losing body fat, I believe that there are other smarter and enjoyable ways to do this. As a starting point, I always look at food quality as this automatically tunes the appetite to eating less energy-dense foods, which should help establish an optimal body fat level over time.

Lastly, fasted training is a refined tool and should only be used sensibly and within the correct context. You shouldn’t be doing it because you’re following the latest trend or because your mate is doing it. However, if you actually enjoy fasted training and feel like it works for you, I wouldn’t try to stop you, but I would urge you to be cautious.