Intermittent Fasting and Running

Intermittent fasting has quickly become one of the most popular dietary strategies of the decade. Over the last few years, it has evolved from a niche topic into something that everyone is doing.

And with evidence it can boost health and help promote fat loss, why shouldn’t they?

But is it a good fit for runners?

What is Intermittent Fasting (IF)?

Intermittent fasting (IF for short) describes small periods of eating that are broken up by longer periods of not eating (AKA fasting).

While this may sound like an odd dietary strategy, you need to remember that we all fast during the night while we sleep. Overnight we abstain from food, and then break our fast (break fast… breakfast… get it?) the following morning.

As a result, ‘intermittent fasting’ describes a range of eating patterns that have you extend your overnight fast for a few hours.

For the sake of simplicity, in this article we are going to be talking about the most common form of intermittent fasting which is also known as time-restricted feeding. This intermittent fasting is the type that revolves around simply extending your overnight fast until it lasts about 16 hours.

In this scenario you would cease eating food at about 8pm and would not eat again until about 12pm the following day.

See, simple.

What are the benefits of IF?

When you extend your overnight fast by a few hours, your body reduces its secretion of the hormone insulin. Concurrently, it also increases its secretion of human growth hormone, while lowering inflammation throughout your body (Ho, 1988; Heilbronn, 2005, Mattson, 2018).

As a result, intermittent fasting can result in:

An enhanced ability to burn fat for energy
Improved insulin sensitivity, and lower resting blood sugar levels
Reductions in blood pressure
Improvements in blood cholesterol
A reduced risk of cardiovascular disease and diabetes.
Improved brain function

Importantly, for a lot of people it also makes it easier to maintain an energy deficit – which aids in fat loss.

But how in the world does this impact runners?

Is IF good for runners

Well, when it comes to intermittent fasting and runners, there are two trains of thought.

Firstly, athletes who have lower body fat percentages tend to have less ‘dead weight’ to carry around. This means that IF can make them more efficient, by helping them reduce their body fat percentages.

Secondly, you will notice above that the first benefit of IF that I touched on was the ability to break down fats for energy in a more efficient manner – and this is important.

See, during long distance running events (like marathons, for example), you are exercising aerobically for 99% of the event. This means that you will be using a good mix of fats and carbohydrates for energy.

And in essence, the more effectively you can break down and use fats for energy, the better off you will be.

This means that implementing intermittent fasting into your daily routine may have the ability to improve your running performance by making you more efficient.

However, it is important to note that performing your running in a fasted state may not be the best idea…

Fasted running benefits

If you choose to go for a run in a fasted state, there is one key thing that occurs – you breakdown and use more fats (and less carbohydrates) for energy than you would in a non-fasted state.

At face value, this might sound like a good thing.

I mean, if fats are our best source of fuel during aerobic activity, wont this make us more efficient during running – especially if you are running long distances?

Well in short, no.

Very simply, the reason that you break down more fats in a fasted state is because you have less carbohydrates available for energy.

More of energy must be derived from fats.

Interestingly, over long distances this has been shown to have a small reduction in endurance running performance in several different studies (Zouhal, 2020).

Importantly, this detriment to performance becomes even more significant during shorter running races like sprints and middle distance events, where carbohydrates are the most predominant source of energy.

But that doesn’t mean that fasting should not be implemented in runners – just that it should be done carefully.

What is the ideal IF schedule for runners?

We know that IF can enhance your capacity to use fats for energy and aids in fat loss – but we also know that running fasted may reduce performance.

So how should we do it?

Well, very simply, you should try and employ the method of fasting discussed above on days where you either train in the afternoon, or don’t train at all – and avoid it on competition days, and days where you train in the morning.

For example, those days where your train in the afternoon, your meal timing might look something like this.

First meal of the day at 12pm
Training at 2pm
Post workout snack 4pm
Last meal of the day (dinner) 7pm

In this manner, your rest days would look extremely similar, just without the run.

This would allow you to reap all the benefits of intermittent fasting while ensuring that you can train at your peak.

Does IF improve run recovery?

Building on this notion a little further, there are some people who firmly believe that IF can improve recovery.

But research would suggest that this is not the case (Burke, 2010).

One of the most important aspects of recovery is having enough energy and nutrients available to repair and rebuild your damaged tissue. In short, without having adequate nutrients available, your ability to repair is impaired.

As a result, fasting after exercise may have a detrimental effect on recovery.

While this can be mitigated by using the intermittent fasting schedule suggested above, it is still an important point to touch on. It also suggests that during periods of extreme training, it might be best to avoid fasting altogether.

Related Article: Does Dark Chocolate Aid In Muscle Recovery?

Tips for runners to get started on IF

Well, to be honest, it is pretty simple:

Stop eating around 8pm at night
Skip breakfast and do not eat your first meal until about 12pm the next day
Drink lots of water
Feel free to use no-energy beverages like black coffee and green tea to blunt your hunger and keep your energy levels high
Eat normally when you break your fast (i.e. fasting does not give you a license to eat whatever you want)

Like I said – simple!

Take Home Message

Intermittent fasting appears to be a useful strategy for runners that can enhance their ability to use fats for energy and strip off any unwanted body fat. However, as exercise performance can be impaired when training in a fasted state, it needs to be used carefully.

References

Heilbronn, Leonie K., et al. “Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism.” The American journal of clinical nutrition 81.1 (2005): 69-73.

Ho, Klan Y., et al. “Fasting enhances growth hormone secretion and amplifies the complex rhythms of growth hormone secretion in man.” The Journal of clinical investigation 81.4 (1988): 968-975.

Mattson, Mark P., et al. “Intermittent metabolic switching, neuroplasticity and brain health.” Nature Reviews Neuroscience 19.2 (2018): 63.

Zouhal, Hassane, et al. “Exercise training and fasting: current insights.” Open Access Journal of Sports Medicine 11 (2020): 1.

Burke, Louise. “Fasting and recovery from exercise.” British Journal of Sports Medicine 44.7 (2010): 502-508.

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