Ask The Expert

Is Intermittent Fasting Good For Running? (Experts Answer)

We asked a select group of fitness and nutrition experts for their take on whether intermittent fasting and running are a good match

Is Intermittent Fasting Good For Running?
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Intermittent fasting has become more popular in recent years thanks to its supposed health benefits. So, are fasting and running a good mix?

In case you didn’t know, intermittent fasting is simply a way of eating that involves splitting your time into periods of eating and not eating.

There are various different methods of intermittent fasting, but one popular one is to split the day into a 16-hour fast and an eight-hour ‘eating window’.

Of course, there are many factors to take into account when it comes to fasting and running, such as the length of the run, the duration of the fast and your specific goals.

But, generally speaking, is fasting a good idea if you’re a runner? What do runners need to know about intermittent fasting and what are some of the key points to bear in mind?

We asked a select group of experts for their take on intermittent fasting when it comes to running.

Here’s what they said.

Editor's note: The content on this website is meant to be informative in nature, but it should not be taken as medical advice. Our articles and the products featured in them are not intended for use as diagnosis, prevention, and/or treatment of health problems. Always speak with a certified medical professional before making any changes to your lifestyle, diet, exercise routine, and/or taking any supplements.

Clarify Your Goals Before Trying Intermittent Fasting

Eleanor Baker, Sports Dietitian and Nutritional / Dietary Advisor For Athletes at Tagalong

When it comes to intermittent fasting and athletic performance, the results from the research are mixed.

There are a variety of ways to approach intermittent fasting, from a 12:12 or 16:8 hour fast that includes your sleep time, to the 5:2 approach, where you eat normally five times a week and practice a form of fasting for two days.

As a dietitian, when I am talking to an athlete who is considering fasting, my first question is ‘what is your goal with fasting?’

There are a variety of reasons why humans have historically fasted and with fasting trending as a diet these days, I find it is important to take into account the motives for implementing it.

I then consider if it is best for that individual. Research has found that those practicing fasting, specifically the 12:12 or 16:8 approach, have seen a reduction in fat mass.

Group running

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While this does not necessarily equate to performance enhancement, it can be desirable by some.

There have been trials where athletes have practiced in a fasted state to increase insulin sensitivity and increase glucose uptake by the muscles, which can have a performance benefit.

Regardless, if you do consider trying out fasting, you really need to listen to your body and what feels good.

I encourage keeping a log of food intake, timing, symptoms and performance to help you better understand how it’s benefiting you.

Also, if you find that fasting is turning into a binge and restrict form of dieting, you should talk to a dietitian like myself to come up with a better eating plan that fits your unique needs and eating patterns!

Intermittent Fasting

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The Jury Is Still Out On Fasting And Athletic Performance

Dr Rami Hashish, Body Injury and Performance Expert

There are various potential benefits of intermittent fasting, including promoting weight loss, reducing blood sugar levels and blood pressure, and protecting against certain diseases.

However, when it comes to athletic performance, the jury is still out.

Preliminary evidence indicates that intermittent fasting may improve aerobic capacity, but has no real effect on anaerobic capacity, muscle strength, or running performance.

A benefit of training while fasted is you may potentially burn fat to fuel your workout, as your glycogen storage (i.e. carbohydrates) is likely depleted. The potential downside is that you also run the risk of breaking down muscle.

Therefore, the key to a successful training schedule while fasting is proper nutrition when you are not fasting.

With that in mind, always maintain proper water and electrolyte consumption to prevent dehydration. Also aim to eat a meal immediately following training to replenish your nutrients.

If engaging in strength training, it may be wise to incorporate more carbs into your diet the day before training. Following training, try to consume more protein to support recovery.

Most importantly, remember to listen to your body.

A common intermittent fasting protocol is fasting for 16 hours with an eight-hour ‘eating window’. That may be too aggressive – particularly at the outset – so pace yourself to allow for healthy habits to develop.

Man Running On Road

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Fasting Is A Tool That Can Be Used When Necessary

Brett Durney, Personal Trainer and Co-Founder of Fitness Lab

When I’m presented with questions like these by my clients, I always respond with the following: it depends.

We all know that there is no one-size-fits-all approach with health, fitness and nutrition. As such, my thoughts about intermittent fasting and running would revolve around the person’s specific goals.

That being said, both running and intermittent fasting are excellent tools to utilise for fat loss.

Essentially, what you are looking for when it comes to fat loss is a calorie deficit across a sustained period of time (both fasting and running can create this).

When it comes to building endurance for ultra events such as Iron Mans or marathons, the use of intermittent fasting should be considered carefully.

This is because you’ll need to ensure that your natural stores of glycogen are replenished frequently, so that you body has enough energy readily available to complete the set distances at a given intensity for a desired period of time.

Although it is possible for humans to complete extraordinary feats on very little fuel, as a regular activity I would personally not recommend this approach.

Woman Running in Park

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If your training sessions tend to be in the mornings, fasting can be a great approach for those who can’t train on full stomachs. This alone makes it a super useful tool in training and running.

However, there are also some potential downsides to fasting and running.

Exactly when you choose to fast and train can dramatically affect your performance in exercise. It’s therefore important to understand why you are using fasting as a tool and what you are ultimately trying to achieve. Most people dive in blind, not really knowing why they’re doing it.

Additionally, if you’re completing an endurance event which utilises your anaerobic / lactate systems, you run the risk of performing at a lower level due to lack of energy.

Depending on your goal, don’t feel you have to do it everyday! It doesn’t have to be black and white.

Intermittent fasting is a tool and can be used when necessary. Be smart about how when and how you use the tool.

Man Running

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Intermittent Fasting May Be Helpful For Runners

Lisa Richards, Nutritionist, The Candida Diet

Intermittent fasting, which can also be referred to as ‘fasted cardio’, may be helpful for runners.

The ‘fasted’ state occurs when the digestive system is void of food, which typically takes between six and eight hours to accomplish.

This makes the ideal fasting period, for those who subscribe to the practice, to be around six to eight hours prior to exercise.

For most people, this means hitting the gym or the road on an empty stomach first thing in the morning, after a full night’s sleep.

However, the question has to be asked, is this a good idea? The idea is that your body may burn more fat because it is void of as much glycogen, carb stores, to use for energy.

Woman Running

(Photo: Adobe Stock)

At this point, studies are showing minimal difference between exercise in a fasted versus a fed state.

However, some people note that their exercise performance and quality is improved when fasting.

This could potentially be a benefit when it comes to weight loss, as the body could be pushed harder and for longer periods, leading to more calories burned.

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