Fasting and Exercise

Training in a Fasted State

The benefits of fasted training is a controversial topic, especially when it comes to fat loss. Studies comparing fasted and fed training in individuals following a ‘regular’ eating schedule with the same caloric intake, where fasted training was performed in the morning followed by a post-workout shake, found that although fatty acid oxidation is increased during fasted exercise, total fat loss over time is unchanged.[35]

This shows that fasted and fed training has the same effect on fat loss when performed with a normal eating schedule, providing the same daily calories are consumed.

So, waking up early to squeeze your cardio in before breakfast isn’t going to have any advantage over performing that training later in the day, provided your net energy balance over the course of the day is the same.

When a similar protocol was performed in physically active men who were fasting during Ramadan, training after 15-16 hours of fasting, a great representation of intermittent fasting, the results differed slightly.

Body fat percentage (BF%) in the fasted group decreased by 6.2%, but the BF% of fed remained unchanged during the whole period of the investigation.[36]

However, in this study, caloric restriction was not controlled, and the fasted group reported a slightly lower caloric intake during periods of the study.

Again, standing to reason that fasted training is not beneficial over fed training for fat loss, provided total energy balance over the day is the same.

So, what are the benefits of fasted training?

As displayed by the fasted group during Ramadan, performing fasted training can make finding a calorie deficit easier.

Training dissipates hunger, so any hunger you carry into a training session soon fades away.

Once you’ve completed your session, you will need to refuel, regardless of the food you ate prior, and so for those who trained fasted, they will have consumed less calories up to this point, facilitating weight loss.

Training fasted can also be used as a method of lengthening your fast.

If you train at the end of your fast, the session will carry you through what may usually be a difficult period to abstain from food.

With hunger dissipated, you may have added an hour or two onto your fast with no extra difficulty.

When training fasted, you’ll also be clear from any interruption from digestion.

Once blood flow and energy towards digestion is removed, your body can be fully focused on supplying those resources where they are required for training.

A key point to be aware of is that fasted training doesn’t majorly interfere with muscle development, having said this, it may be sub-optimal for growth.

The same men who fasted during Ramadan, lifting weights after 15-16 hours of fasting, found that body composition wasn’t impacted when compared to those who trained fed.

A final benefit of fasted training is increased metabolic flexibility.

Fasting alone increases metabolic flexibility by allow your body to tap into and effectively use fat stores for energy.

Extending this into a training environment, where the energy demands are higher, allows you to become better accustomed to accessing stored fat and using it for fuel.

This is a point of focus for many endurance athletes that perform fasted training.

Can You Train in the Morning and Continue Your Fast into the Day?

In my opinion, this is more of an advanced technique... Say you normally break your fast at 2:00pm, you can train at 8:00am and continue fasting until your usual time and still reap the rewards of that session.

Should you provide your body with the correct nutrition in your feeding window, it’s not going to disappear overnight. Having said this, intensity and frequency most certainly matters. A taxing session, especially resistance training, should be followed up immediately with post workout nutrition, ideally in the form of a combination of protein and carbohydrates.[37]

But What About Endurance Training?

As I’ve previously mentioned, fasted training has become an integral part of endurance training and competition. The 2018 Kona Age Group World Champion, who also set the course record in the event, Dan Plews, is an advocate of fasted training and claims that being able to utilise fat for fuel is an integral part of endurance racing.

I am not an expert in the field of endurance; however, through my own experience and research, the following recommendations can be made here:

Keep fasted workouts to a low intensity, so you don’t overtax your body and immune system, integrating a selection of fasted and fed training, tending towards fed training for the intense sessions.
Ensure that if you are training again soon after or require optimal recovery from the given session, you consume a post-workout meal with roughly between a 3:1 - 4:1 carb:protein ratio.[38] A perfect example of this would be a peanut butter jelly sandwich! For 1 slice of whole wheat bread, 1 tablespoon of peanut butter and half a tablespoon of all fruit jam, you should be just in the right range. </aside>

Please consult your doctor to ensure that you are aware of any hormonal imbalances or other health issues that may lead you to refrain from fasted training; this is especially the case for women. Practice fasted training at your own discretion and moderate the frequency, duration and intensity of sessions.