NEW!Incredible offer for our exclusive subscribers! Read More
Cross Training For Runners

Intermittent Fasting for Runners – The Complete Guide

13 Mins read

Running and intermittent fasting can mesh well if you do it right.

Today, I will share with you all you need to know about this practice, along with a few practical diet and training tips to help you proceed with this method without fail.

In this article, I’ll dive into the following:

  • What is intermittent fasting
  • The benefits of intermittent fasting for runners
  • The dangers and limits of intermittent fasting for runners
  • Can you run while intermittent fasting
  • And so much more

Let’s get in.

Intermittent Fasting – The Definition

Intermittent fasting consists of fasting and eating over a defined period.  It’s an eating method that cycles between fasting—calorie restriction—and normal eating during a specific period.

Intermittent fasting limits how much food eats for a given period, followed by an interval of normal eating known as the feeding window.

You’ll be fasting –not eating—for a period ranging from 16, 20, to even 36 hours, depending on your chosen IF method.

Intermittent fasting is not new. It has been practiced for millennia and used by many religions—mainly Judaism and Islam— for healing and spiritual enlightenment.

These belief doctrines regard fasting as a powerful healing method that allows the human body to take time out from the food toxins present in our bodies and as a means for reaching higher spiritual existence.

What happens To Your Body When You Fast

The fed-fast cycle your body goes through  changes your metabolism and hormone levels. And this is the case whether you opt for a whole-day fast, time-restricted feeding, or alternate-day fasting.

Let’s dive into what takes place inside your body during a fast.

The Feeding Phase

During the feeding period, the body digest and absorbs nutrients from food. As this happens, your blood sugar levels and insult production increase. Insulin helps carry glucose from your blood into the cells to be used or stored for fuel. In most cases, extra glucose not immediately burned off for energy is either stored in your liver and muscles as glycogen or turned into triglycerides and stored as fat.

Technically called the anabolic growth phase, the first few hours after eating is the feeding period. Your body employs the fuel you just consumed to power your activity and for tissue and cellular growth. Your pancreas releases insulin. This hormone lets your body use up glucose after eating to sore any excess fuel in your cells for later use.

The first 4 to 18 hours in a fasting state

The size and content of your last meal impact how long you stay in the feeding phase, but usually, your body starts to access the early fasting state within 4 to 6 hours after your last meal.

As your body switches from a fed to a fasting state, insulin levels drop since no carbs are consumed from food. At the same time, leptin plummets, and ghrelin increases. Thanks to the absence of food, your body starts to burn off its fuel stores.

Around 8 hours of fasting, your liver will burn off the last of its glucose reserves. At this stage, your body enters a state known s gluconeogenesis, which marks the transition into fasting mode.

At first, your body taps into muscle and liver glycogen and switches back into glucose as you exhaust your glycogen stores. Next, your body secretes lipolysis, which converts fat into triglycerides as an additional energy source. As lipolysis levels peak, your body breaks down protein—including your hard-earned muscles—as a source of glucose for your brain and red blood cells, which rely mostly on glucose for energy.

Once you’re passed the 16-hour mark, glycogen in your liver and glucose in your cells diminish quickly. This, in turn, causes your body to turn int its stored fat to meet its energy needs. In most cases, your energy needs at this stage remain the same. You’re still likely working, walking, running errands, and even working out—so how much fuel you need can be substantial.

About 18 To 48 Hours Into A fast

The fasting state starts around 18 to 48 hours after your last and lasts until day seven. This is the most challenging part of the fast for most people.

Roughly 18 hours into skipping meals, your body will go into full-on fasting mode. Your body’s glycogen levels are likely completely exhausted at this mark, leaving protein and fat as the primary fuel source. Because of the low insulin level, some fatty acids might get converted into ketones, which sets the stage for your body to enter a metabolic state known as ketosis.

During this stage, you might notice changes in your feelings and physical appearance. You start entering ketosis around 18 to 48 hours after your last meal.

You know what ketosis is all about if you’re into the keto diet. Not the case? No problem. Ketosis is a metabolic state in which your body burns fat as the main source of energy instead of carbs or protein.

Ketosis is a crucial phase of the fast during which your body begins to use its fat reserves as the main energy source. as you fully transition into ketosis, you might stop feeling tired and hungry. That’s why achieving the state of ketosis is highly sought after in the keto community. Eating the right foods and fasting for just enough can be all you need to kick off this fat-burning process.

Again, how fast you access the state of ketosis depends on the content of your last meal -high fat, low carb Vs. High carb, low fat, for example—and your last meal timing. f you eat low carb—anything less than 100 net grams of carbs per day—your body will transition into ketosis on the earlier side.

Prolonged Fasting – over 48 hours after your last meal

Shunning food for more than a few days is considered long fasting.

Around the 48-hour mark, your body relies heavily on ketones and muscle protein for fuel.

Additional resource – Can Running Help Cure Your Hangover?

Over 48 hours

Once you’ve been fasting for over 48 hours, your body enters a deep state of ketosis. If you’re planning to fast this long, I’d recommend that you put some planning into how and when you’ll start the fast. Try choosing a day and time, and then take the right precautions for the duration of your fast. It never hurts to be careful..

Just keep in mind that shunning food and nutrients for this long isn’t recommended for most people and should only be practiced under medical supervision. You’ve been warned

intermittent fasting for runners

The Benefits of Fasting

Intermittent fasting has gathered so much steam over the past few years thanks to the many health benefits such as improved insulin resistance, weight loss, cellular repair, weight loss, and mental clarity.

Let’s briefly discuss some of the benefits.

Lose Weight

Looking to lose weight? Fasting may boost your body’s fat-burning potential.

Here’s the truth. Restricting your food intake during certain times of the day is a powerful hack for losing the pounds quickly and keeping them off. When you fast, your body runs out of its main fuel source—glucose, thus forcing the body to switch to using fat as the main energy source.

Don’t take my word for it. Research from the Proceedings of Nutrition Society revealed that intermittent fasting boosts metabolism and greatly affects insulin sensitivity and fat loss.

Another research out of the Annual Review of Nutrient showed that prolonged overnight fasting might improve gut health in subjects.

That’s not the whole story

A study published in the International Journal of Obesity revealed that intermittent fasting leads to great weight in obese men.

Faster Ketosis

It’s also great for people on the ketogenic diet. Intermittent fasting may assist your body in attaining ketosis faster than the keto diet alone.

Live Longer

Intermittent fasting can also help you live longer. According to a study by the University of Southern California’s Longevity Institute, fasting decreases the release of IGF-1, an insulin-like growth factor that drives the aging process and activates other DNA repair genes.

Reduce Diabetes

Studies have reported that intermittent fasting can improve blood sugar and metabolic health by decreasing blood sugar, insulin resistance, and fasting insulin levels. These, in turn, can help prevent or reduce the severity of type 2 diabetes and other chronic conditions.

For more on the benefits of fasting, check the following research papers:

This is great and all, but what about runners? Does intermittent fasting help? Let’s check them out.

What Are The Health Benefits Of Intermittent Fasting For Runners?

 A lot of research suggests some fitness and health benefits of intermittent fasting for runners.

Research out of the British Journal of Nutrition that looked into male runners reported that training in a fasted state could improve fat-burning capacity, which is key for long-distance running during which glycogen stores might be depleted.

A study published in the Journal of Applied Physiology found that participants who regularly trained in a fasted state over six weeks experienced more endurance improvement than those who ate before exercising.

A study found that IF may improve post-workout recovery by improving nutrient absorption and reducing inflammation.

A meta-analysis out of the Journal Nutrients reported that intermittent fasting might help reduce the body, decrease fat mass, and improve VO2 max.

I can go on and on, but the picture is clear – Intermittent fasting has much to offer runners.

Intermittent fasting and running performance

Although the impact of IF on overall health has been heavily scrutinized, especially in overweight and diabetic individuals.

Although research on runners is limited, intermittent fasting can help athletes improve performance markers such as body composition, sustained performance, inflammation response, and improved immunity.

Can you Do Intermittent Fasting Without Sacrificing Performance

It depends. Are you a competitive runner? Do you have an important race in mind? If that’s so, then intermittent fasting will hamper your training. This is especially true if you’re not used to training in a fasted state.

But if you want to lose weight and shift body composition while running, then intermittent fasting might help.

An experiment that examined elite cyclists given an 8-hour feeding window shed weight, improved their body composition, and performed similarly during the 4-week high-level training period.

The fasting athletes also experienced increased power out related to body weight thanks to the weight loss.

That’s not the whole story. Research has also reported that time-restrictive eating could reduce inflammation and offer a protective impact on the immune system.

That’s not the whole story.

Research has been performed on athletes who fast during the holy month of Ramadan from dawn to sunset.

Though the typical Ramadan fasting protocol is different from the standard intermittent fast (during which water or any other nutrient or liquid intake isn’t allowed), the research has reported that athletes who kept the same non-fasting fuel and macronutrient intake (and other variables such as sleep) didn’t experience any drastic performance issues while fasting during Ramadan.

So what’s the conclusion?

According to the research, one can assume it’s possible to maintain performance while intermittent fasting as long as your overall fuel intake, sleep, and training isn’t adversely impacted.

I’d say it’s safe for recreational runners to practice intermittent fasting, but if you try going on a long fast in the middle of a serious training cycle, you risk losing your gains.

If you’re a serious endurance runner, I’d recommend keeping your runs around the fasts easy since mixing intense training with fasting can have dire consequences that can hurt your performance and recovery.

The Downsides Of Intermittent Fasting

The benefits of intermittent fasting can vary from one person to the next.

And it’s not for everyone.

There is a catch to it. To get the most out of this diet, you must know its downsides.

For starters, hunger is the biggest issue.  Going for long periods without food is something we in the developed world are not used to.

Going for a long or hard run during the fasting period’s end could leave you dizzy or completely exhausted. That’s why this is your first time doing intermittent fasting, you should ensure you’re keeping your runs easy. Otherwise, you could be putting your fitness and health at risk.

What’s more?

A review published in the Journal of Sports Medicine on Fasting’s effect on athletic performance reported no clear evidence and suggested that endurance athletes should avoid intense training while in a fasted state.

Because of a lack of fuel, you also run the risk of performing at a mediocre level.  If you had an easy run on schedule, this should be no problem, but a quality run—a long run or interval work—can be greatly affected.

Is It Good For Runners?

I hope I had a straight answer, but I don’t. There’s no universal all, and whether intermittent fasting is healthy for you as a runner depends on a few variables such as your running routine, training frequency and intensity, body weight, training goals, lifestyle, and overall health.

No suit fits all.

Before you give intermittent fasting a chance, it’s key to consider your running plan, the types of sessions you do, and how your body responds to training overall.

Runners That Should Not Fast

Despite the many fitness and health benefits, skipping meals isn’t for everyone.

Since If limits your caloric intake, you should avoid it if any of the following applies to you:

  • If you find it hard to gain weight
  • If you’re underweight
  • If you are pregnant or breastfeeding
  • Have a history of eating disorder
  • Have chronic conditions such as high blood pressure, diabetes, or heart disease.

Fasting may have dire side effects if the above applies to you.

Intermittent Fasting and Running  – How To get Started

Now that you know a thing or two about intermittent fasting and how it can help (or hurt) your running performance, let’s dive into how to make the most out of it.

Sounds great

Let’s get started.

Don’t Eat Crap

Just because you are fasting doesn’t mean you can eat whatever you want during the feeding window.

That’s a common mistake.

People who fast are much more likely to binge and reach for high-calorie foods when they eat again.

There are many various ways to start intermittent fasting.

The method may differ in the number of fast times and calorie allowances.

People have different needs; therefore, different styles will suit them and help them get the most out of practice.

There are many ways to start intermittent fasting.

Just like any other health program, how you get started hinges on your fitness goals, workout routine, physiology, genes, and lifestyle—to name a few.

Break The Fast Right

Once it’s time to break the fast, go for a meal with plenty of complex carbs and proteins.

In other words, stick to healthy food choices.

Or it’s a no-deal.

Low Intensity

If this is your first time doing intermittent fasting, keep your runs at an easy pace, around 3 to 5 out of 10. When you stick to this pace, you’re mainly burning off fat as energy instead of glycogen will be depleted in a fasted state.

I’d recommend the Maffetone method (which also works great if you’re in the base building phase of a training cycle).

You might risk hitting the wall if you try to push the pace. You should never try your run your hardest while starving your body of energy. You won’t get that far.

Run Short

Another thing you can do is limit your training duration. For example, you don’t want to run for over 90 minutes in a fasted state.

As a rule, increase your running duration as you get more comfortable training in a fasted state. This, believe me, doesn’t happen overnight.

Feeling weak or dizzy in the middle of a run? Then either slow down or refuel with carbs and protein to give your body the energy boost it needs. A snack should help.

Choose The Right Time

I’d also recommend that you schedule your runs and workouts while fueling.

Running first thing in the morning in a fasted state? Then refuel the moment you’re done running. Refueling immediately helps you avoid muscle waste and speeds up recovery. That’s a good thing if you ask me.

Supplement Just In Case

During intense training days—if you have any speedwork or long run scheduled—take a supplement, such as BCAA.

Here are a few recommended dosages:

5 g of BCAAs before your run

5 to 10 g of BCAAs during long running sessions, and

10 to 15 of BCAAs immediately following a hard run.

Fasting Protocols For Runners

There are many ways to approach intermittent fasting.

Your chosen method depends mostly on your fitness goals, workout schedule, physiology, personal preference, lifestyle conditions, and other factors.

Here are the main protocols.

  1. The Periodic Fast

If you’ve never tried fasting before, then the periodic fast should be your trial fast—Your opportunity to take IF for a test drive before committing to anything serious or long-term.

Also, if it’s your first time doing it, write down your thoughts and notes, then use them as a reference for future practice.

The How

This method entails a fast for 24 hours, starting at any time of the day, preferably on a Sunday.

You can start at a specific time, on Saturday at 11 pm, for instance, drink plenty of water, then break your fast on Sunday night.

For the most part, you should not do this method more than once or twice a week.

  1. The Warrior Diet

The Warrior Diet consists of 20 hours of fasting, then a four-hour feeding period, and consuming one healthy meal daily.

This method can help you boost energy levels, shed weight, increase muscle mass, and save money.

The How

During the feeding window, usually, during dinner time, go for one large meal, aiming for roughly 2000 calories (or more, depending on your needs) in one sitting.

For the best results, put the feeding window at the end of the day, as it’s more suitable for family dinners and post-run sessions.

If you have a run or workout on the schedule,  plan it at the end of the fast.

  1. Leangains

The Leangains method was made famous by author Martin Berkham, consisting of a 16-hour fast (from 10 p.m. to 2 p.m. the next day, for instance), followed by an 8-hour eating window.

This method is great to increase muscle gains while shedding fat.

To make the most out of Leangains, skip breakfast daily, then break your fast roughly eight hours after waking up.

During the leangains approach, ensure the bulk of your calories during the post-run window, following a diet high in protein, complex carbohydrates, and some healthy fats, like olive oil and avocados.

The How

For example, on this plan, you’d fast from 9 pm Monday until 1 pm Tuesday.

If you were planning to run, you’d do it on Tuesday afternoon.

  1. Alternate-Day Fasting

This is similar to the last method but involves eating within a 24-hour window followed by 24 hours of true fasting every two-day cycle.

In other words, you simply eat every other day with this method.

According to research by the University of Illinois at Chicago, the Alternate-Day Fasting approach promotes weight loss and decreases the risks of coronary artery diseases.

During the feeding period, you can eat what you want and aim for a broad range of healthy food choices—especially if the 24-hour fast is too much.

The How

This is simple.

All you have to do here is fast one day and eat healthy the next day.

Listen to your body

Ultimately, you are the boss and can decide which approach works best for you.

With that said, to do that, you need to keep in mind that it’s of paramount importance to listen to your body’s signals of pain and discomfort—mainly your hunger signals.

Intermittent Fasting For Runners  – The Conclusion

There you have it! If you ever wanted to try intermittent fasting while running, then today’s post should get you started on the right foot. The rest is just details.

Please feel free to leave your comments and questions in the section below.

In the meantime thank you for dropping by.

Keep training strong.

David D.

Related posts
Cross Training For Runners

The Ultimate Guide to Finding the Perfect Fit for Your Running Shoes

8 Mins read
Are you ready to unravel the mysteries of the perfect running shoe fit? Well, you’re in luck because you’ve stumbled upon the…
Cross Training For Runners

How to Lose Weight? Top 4 Tips and Tricks

2 Mins read
People aspire to lose weight for all sorts of reasons. They fall into so many con traps of products promising to help…
Cross Training For Runners

20 Essential Safety Tips for Running in Busy City Streets"

14 Mins read
Running outdoor is awesome. It will keep you sane, healthy and will get you into the best shape of your life. It’s…