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Cross Training For Runners

Can You Run ON The Keto Diet? How to Combine Keto & Running

8 Mins read

Are you looking for ways to combine keto and running in a safe way?

Then you have come to the right place.

Carbs are the primary energy source on the run.  It’s, in fact, the reason so many runners load up on pasta and bread the night before a long run. Carbs are key.

But over the past few years, the keto diet—a nutrition plan known for its super carb restrictions—has gathered a lot of steam in the fitness world.

And as far as I can tell, a lot of runners from various backgrounds are also embracing this trend.

But can you really run on the keto diet? Is it possible?

In short, the answer is YES—as long as you do it the right way (and are willing to make some sacrifices along the way).

In this article, I’ll share a few practical guidelines on how to adopt the keto diet as a  runner.

More specifically, I’ll look into the following:

  • What is the keto diet
  • The background of ketosis
  • The pros of the keto diet
  • The cons of the keto diet for runners
  • How to keto the safe way
  • And so much more

Sounds great? Let’s get started.

What Is The Keto Diet

In essence, the keto diet is a high-fat, mild protein, and super low carbohydrate diet.  It’s similar to the Atkins diet and other low-carb diets, but to properly follow the diet, you’ll need to get into a state of ketosis.

The idea is that you eat a lot of fat and severely restrict your carb intake to exhaust your body’s carb stores and force it to tap into fat for energy.

Doing this forces your body into ketosis, a metabolic state where your body switches to burning fat for fuel since it doesn’t have enough carbs for energy.

During ketosis, your body starts to make ketones for fuel—derived from fat—instead of glycogen which mainly comes from carbs.

When you achieve complete ketosis adaptation, you’ll use fat as your primary fuel source.

There are many methods to check whether you’re in ketosis—some of which I’ve already gone into great detail about in this post.

Additional resource – Keto marathon training

The Meaning Of Keto Adaptation

Keto-adaptation, or what’s referred to as fat-adapting, refers to the metabolic jump from carbohydrates to fat as the main energy source.

According to current scientific literature, fat-adapting may take anywhere from 4 to 12 weeks, depending on variables such as your diet, physiology, metabolism, training habits, etc.

running on keto

Staying In Ketosis

To stay in ketosis, your carb intake should be limited to around 30 to 50 grams per day—depending on your activity level.

The more running you do, the more carbs gram you can get away with. Here’s a list of the off-limits foods on the keto diet.

  • Bread
  • Fruits
  • Starchy vegetables like beets and potatoes
  • Legumes
  • Beans
  • Lentils
  • Beer and alcohol
  • Many condiments and sauces high in sugar
  • Any other sugar-rich food item

You get it. If it has carbs in any form, you shouldn’t be eating when you’re trying to adhere to the ketogenic diet.

As you can already tell, switching to the keto diet will most likely mean a complete diet makeover—especially if you’re used to eating a lot of carbs.

Additional resource – Probiotics For Runners 

The Benefits of Keto And Running

Here are some of the acclaimed benefits of the keto diet.

Note – Please keep in mind that research on the keto diet’s effectiveness for runners is still inconclusive. Most of the evidence is anecdotal so take it with a grain of salt.

The Wall and Fat Store

If you’re familiar with endurance training, then you know that your body requires nonstop carbohydrates intake to keep going.

How come?

The human body can only store a limited volume of glycogen—roughly 500 grams in muscle and liver cells. That’s around 2000 calories of fuel.

As you can already tell, 2000 calories ain’t enough to sustain you through a whole marathon. That’s why marathon runners need energy on the go. They need the extra fuel to keep going.

However, the theory is if you’re completely keto-adapted, you might be able to tap into a more abundant energy fuel source, which is your body fat. In fact, body fat packs roughly 20 times more calories than glycogen, even in a lean runner.

In theory, if you’re truly keto-adapted—as in, you’re using fat as the primary source of energy—the wall, or what’s known as bonking, may disappear.

Since the keto diet forces your body to use fat as its main source of energy, there’s a chance that it can help you avoid hitting the wall during endurance running.

Additional Resource – Here’s how to create a running program

Improved Body Composition

Logging the miles on the keto diet can help you burn fat and achieve your body composition goals. I lost over 12 pounds and improved my body fat percent by over 4 points the first month I went on keto.

Science also backs up the power of keto for losing weight. This research, for instance, has revealed that the keto diet can positively impact one’s body composition when combined with moderate-intensity training.

Here are more research papers to check out:

In essence, the keto diet improves your body’s ability to burn fat, both at rest and during training. This, in turn, maximizes your fat loss effort while exercising in these zones.

For example, research out of the Journal of Endocrinology reported that the ketogenic diet boosted the production of the hepatic growth hormone, which can be key for youthfulness and strength.

Other benefits of the keto diet include:

  • Improved energy levels
  • Better sleep
  • Enhanced cognition and focus
  • Improved weight loss
  • Improved body composition
  • Improved heart health
  • Helping reduce seizures
  • Improve acne
  • Protect brain function
  • Improve PCOS symptoms
  • And so much more

Additional resource – Best supplements for runners

The Downsides of Keto While Running

As you can already tell, the keto diet is a controversial subject in running circles.

I hate to sound like a broken record, but runners love their carbs as they’re the main energy source on the run.

This makes the likelihood of suffering a few downsides—or a lot—more likely once you start restricting your intake of this valuable macronutrient.

Let’s check some of the cons of the keto diet for runners.

Additional resource – Keto recipes list 

The Keto Flu

During the early days of a keto diet, expect to experience a plethora of unwanted symptoms.

First, you’ll feel bad—like really bad. This is what’s known as the keto flu among keto fans. It’s, essentially, the result of sugar and carbohydrate withdrawal as well as a change in the gut bacteria and an immune system reaction.

Some of the side effects include

  • Brain fog
  • Irritability
  • Headache
  • Fatigue
  • Nausea
  • Trouble sleeping
  • Cramps
  • Sore muscles
  • Constipation
  • Dizziness
  • Smelly breath

Additional resource – Salt tablets for runners

Muscle loss

An unwanted side effect of keto-related weight changes is a loss of muscle mass.

This is especially the case if you’re limiting your protein intake and/or engaging in prolonged endurance exercise.

Sure, the keto diet is scientifically proven to help people lose weight—and a lot of it. But some of the weight might be muscle as well. Not good at all.

And since fat burns fewer calories than muscle mass, that will impact your metabolism.

That’s why most people who drop off the ketogenic diet tend to regain much of their pre-keto weight and often not in the same proportions. Instead of gaining back your muscle mass, you’re likely to pile on the fat.

Reduced Performance

One of the telling signs of the keto full is diminished performance. If performance matters, this should worry you since complete fat-adaptation takes a while.

So don’t expect to switch into the keto diet and start breaking your PRs left and right. It doesn’t happen that way in the real world.

The opposite is more likely to happen.

Carbs, after all, are your body’s favorite source of energy for running, and without them out, you simply won’t be able to run as long and/or as hard as you’re used to be.

What’s more?

The research on the effectiveness of the keto diet for improving running performance is still in the woods.

That’s why most runners who might benefit from keto-adaptation are those logging a lot of miles at low to moderate intensity—think marathon runners.

Once you log in enough miles, your body needs to start burning off those fat energy stores.

When you’re logging the miles at low intensity, your body will be able to sustain its energy needs from fat. But since glycogen is the primary fuel source during high-intensity exercise, you might be limiting your performance on some runs and workouts to follow a certain diet.

Additional Resource – Why is my running not improving

Fat Adaptation Takes time

Although getting into ketosis might only take a few days, becoming truly keto-adapted might take up to months.

Fat adaptation typically begins between 6 and 12 weeks after entering ketosis, depending on how strictly you follow the keto diet as well your physiology, metabolism, and training load.

For example, research shows that endurance athletes may become fat-adapted faster than the average individual.

For this reason, expect your first few weeks—or months—to suck.

Once you’re truly fat-adapted, you can go the distance. At least, that’s been my experience.

However, keep in mind that, for some reason or the other, some athletes might never be able to fully adapt to endurance exercise while on keto. I know life is unfair and all that, so be careful.

That’s why some of these athletes practice carbo cycling by switching in from a ketogenic diet or might go low-carb during higher training load weeks of training.

The Verdict

So should you really try the keto diet as a runner? Will it work for you?

In the end, it’s really up to you.

I believe that if the keto diet is done right, sooner or later, you’ll be able to tap into your fat stores for fuel.

Overall, the benefits of the keto diet far outweigh the downsides—this is especially the case if you’re willing to sacrifice performance for weeks over long-term health gains.

Note – I hate to sound like a broken record, but if you’ve been logging this mile for a while and then decide to go full keto, your performance will likely plummet—in fact, it might plummet hard. If you have an upcoming race in which you want to break your PR, deciding to try keto might compromise your training.

Additional resource – Best sources of electrolytes for runners

How To do it Safely

So are you really serious about giving the keto diet a try? Then keep on reading.

Keep in mind that keto transition is a big performance and mood damper. Don’t try doing anything strenuous during the first few days.

Keep it light. I’d recommend planning your first ketosis cycle during a time in which you don’t mind if your athletic performance suffers a bit.

How Long Should You Go Keto For?

Again it depends on your lifestyle and training goals.

At the very least, try to stay keto-adapted for months in a year.

Or you can embrace a full Keto lifestyle or remain in, or close to, ketosis all the time—Zach Bitter is one inspiring athlete to emulate.

This elite ultra runner is the 100-mile American record holder, and he’s one of the most known proponents of a high-fat, low-carb eating lifestyle in the fitness world.

So if you want to dip your toe into the keto world while training for a serious endurance event, read upon Zach. The guy is quite inspiring.

However, it’s not easy for most people, including myself, to commit to a lifetime lifestyle of low carb and high fats.

What’s more?

I also love carbohydrates –let’s admit, they do taste better. What’s more?

If you have a family—or any form of social interaction with other humans—sticking to a restrictive keto diet all the time can be quite tricky.

Here’s what I’d recommend you to do.

Day 1

Have a keto friend breakfast and lunch (get the recipes from here), then skip dinner as research shows that fasting for prolonged periods helps you get into ketosis faster.

Days 2 to 10

Start your day with bulletproof coffee—keto coffee with MCT oil—then do your workout—whether it’s running, weight lifting, spinning—but keep it low intensity.

Feel free to take plenty of breaks—take as many walking breaks during your long runs. Don’t try to force.

You should also drink plenty of water.

Through these days, keep your carb intake as long as possible. Remember that the average banana packs in around 25 to 30 grams of net carbs—or the daily recommend income for getting into ketosis.

So one banana is enough to ruin your keto efforts.

Day 11 and Over

It’s up to you.

By this point, you should be in ketosis. Now, fat-adaptation starts.

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