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Cross Training For Runners

Fueling Endurance: How to Optimize Marathon Training with the Keto Die

9 Mins read

Welcome, fellow runners, to the ultimate guide on keto marathon training!

For years, marathon runners have relied on carbohydrates as their go-to fuel source during long training sessions and races.

But what if I told you that there’s another way to fuel your body that could potentially improve body composition, mental function, and energy levels?

But here’s the caveat: “Low-carb and high-fat? Isn’t that a recipe for disaster when it comes to endurance running?”

Well, it’s not that simple.

In this article, we’ll dive deep into the world of keto marathon training and explore the benefits, challenges, and strategies for success.

So, whether you’re a seasoned runner or just starting your marathon journey, get ready to take your performance to the next level with the power of keto.

Running On Keto – Can You Do It?

The short answer is yes. Over time your body will adapt. But the long answer is multifaceted.

Let’s first discuss what the keto diet is all about. Also know as the ketogenic diet, this is a high-fat, low-carb nutrition plan is designed to put your body into a state of ketosis. In this metabolic state, your body relies on fat instead of carbohydrates for energy.

Getting into ketosis and staying there requires a strict diet with fewer than 20 grams of carbs a day. That means saying goodbye to beloved carbs like bread, pasta, and rice. And if you’re new to low-carb diets, the transition can be challenging. But it doesn’t take forever.

Once your body becomes keto-adapted, you’ll experience increased energy levels, improved mental clarity, and even better sleep.

Some runners even swear by the keto diet, claiming that it helps them avoid hitting the infamous “wall” during long runs. Some research has suggested that the keto diet may increase our body’s ability to use fat as a fuel source during exercise. This, as you can tell, can lead to better performance and less fatigue.

Of course, as with any significant dietary change, it’s crucial to consult a healthcare professional before starting a keto diet. They can help you create a personalized plan that meets your nutritional needs and ensures that you’re fueling your body properly for your runs.

Note – Ketosis Is Not Created Equal. Keep in mind that everyone’s body works differently. You might be able to reach ketosis by eating roughly 30 grams of carbs. All while, others may need to reduce their carb intake to 10 or fewer grams per day to be successful.

What Should I Eat On The Keto Diet?

That’s probably one of the most common questions posed by beginners who want to try the keto diet.

It’s simple.

Stock your kitchen with everything you need to reach keto success.

Leave nothing to chance.

Here’s a sample list of keto-friendly foods:

  • Fats and oils, including butter, olive oil, sesame oil, almond oil, and flaxseed oil.
  • Dairy products such as sour cheese, sour cream, heavy cream, and Greek yogurt.
  • Eggs and lots of eggs.
  • Meat, especially chicken, beef, goat, and veal.
  • Fish, including trout, salmon, sardines, catfish, and tuna.
  • Nuts and seeds like walnuts, almonds, pumpkin, sunflower, and sesame seeds.
  • Some fruits, such as avocadoes, strawberries, and raspberries.

Here’s what you need to avoid on the keto diet

  • Grains and starches, including wheat, corn, oats, and rye.
  • Processed foods. If it has carrageenan, don’t eat it.
  • Sugary foods and drinks
  • Low-fat products such as drinks, glute, diet soda, etc.
  • Fruits
  • Root vegetables
  • Beans and legume
  • Alcohol
  • Anything else that has sugar

Additional resource – Best supplements for runners

The Pros and Cons of The Keto Diet For Runners

Just like any other nutrition plan, the keto diet comes with its own set of pros and cons. Let’s take a closer look.

Improved Sleep

Improved Sleep: Are you tired of feeling tired? Once you reach ketosis, your sleep cycle will improve. This means falling asleep faster and waking up feeling refreshed.

According to Natures Rise, you can also leverage mushrooms to improve your sleep. But why mushrooms? —you might ask.

Well, mushrooms like Lion’s Mane are very low in carbs—therefore, they fit right into the low-carb category of the keto diet. With mushrooms on your side, all you have to worry about is a good source of high fat, and your keto diet will be ready.

Improved Body Composition

Keto works like magic for weight loss. Research shows that it can help you start burning fat quickly and improve your body composition. You can even work out on the keto diet and lose weight without affecting lean muscle mass. For example, this research reported that working out while on keto can boost weight loss from stores without affecting lean muscle mass.

Other than weight loss, the keto diet can help:

  • Improving digestion
  • Improving mental function
  • Lowering the glycemic index
  • Lowering the risk of heart diseases, some cancers, and epilepsy
  • And so much more.

Additional resource – Running with diabetes

The Downsides

One of the downsides of the keto diet is poor performance during the early weeks of the diet. It’s like trying to run a race with flat tires – your body simply can’t keep up. But don’t let this discourage you. Remember, Rome wasn’t built in a day. Becoming fully fat-adapted takes time, and it won’t happen overnight.

That being said, once you’re keto-adapted, you’ll experience improved sleep, improved body composition, and many other benefits.

But what about marathon runners? The keto diet eliminates grains, sugar, and starches – all of which are typically the main source of energy during long-distance running. This can be a major concern for seasoned runners who have relied on carbohydrates for fuel.

But it’s not all doom and gloom. Once fully fat-adapted, the body becomes more efficient at burning fat for energy, even during low to mild-intensity training. Research has shown that fat adaptation can take anywhere from 4 to 8 weeks on the keto diet, depending on metabolism and other variables.

What’s more?

Keep in mind the science is still divided on the long-term impact of the keto diet. While many people have seen great success with the diet, others have not. It’s a personal decision that should be made with careful consideration.

Marathon Training Fueling Needs

Adopting the ketogenic lifestyle means no grains, sugar, starches, loaves of bread, or the sort. This must be triggering all sorts of alarms if you’ve been around the long-distance running block for a while.

After all, aren’t carbs the main energy source on the run?

Most experts recommend that regular marathon runners consume around 400 to 600 grams of carbs daily. That’s over 20 times more than the recommended carb intake on the ketogenic diet.

The truth is a little bit more complicated.

According to my experience, as well as plenty of anecdotal evidence, once you’ve fully fat-adapted, you’ll be running on fat almost as efficiently as on carbs, especially during low to mild-intensity training.

Let me explain more.

Additional resource – Before you sign up for a marathon

Keto Adaptation

While most athletes rely on carbohydrates as their primary fuel source, those who have been on the keto diet for a while can tap into a seemingly endless supply of energy stored in their body fat. This is what’s known as being “fat-adapted,” and it can take anywhere from 4 to 8 weeks to attain.

But what exactly is going on inside your body when you make the switch to fat-burning mode? Well, it all comes down to the molecule that powers your muscles: adenosine triphosphate (ATP).

To produce ATP, your body can use either carbohydrates or fats. When carbs are readily available, your body will use them to create ATP. However, when carb levels are low, your body will switch over to using fat for fuel instead.

The argument for fueling with fats

Here’s the exciting part: research shows that body fat contains around 20 times more calories than glycogen, even in lean individuals. This means that if you’re fat-adapted, you can access a much larger energy reserve than if you were relying solely on carbs.

Of course, this doesn’t mean you should go full-on keto if you’re an endurance athlete. Your body still needs some carbs to function properly, especially during high-intensity workouts. But by limiting your carb intake and training your body to use fat as fuel, you can enhance your endurance and unlock a whole new level of performance.

Research On Keto And Endurance Performance Training

So, what does the research say about keto adaptation and endurance training? Well, there’s a growing body of evidence that suggests that the keto diet can indeed improve endurance performance.

For example, a study published in the Journal of Physiology found that endurance-trained athletes who followed a ketogenic diet for ten weeks had greater fat oxidation rates during exercise and were able to maintain their exercise intensity for longer periods of time.

Let’s look at another research.

Around 40 years ago, Stephen Phinney, a world-famous keto researcher, conducted an experiment that could give us a clue.

He analyzed the endurance of six obese, untrained subjects on a treadmill under two different conditions:

Group I – a normal diet that contained carbohydrates, and

Group II – a hypocaloric ketogenic diet (protein-supplemented fast or PSF).

The result was astonishing. The keto group could stay on the treadmill for around twice as long before becoming exhausted compared to the carb-fed group.

But that’s not all. Another experiment had 20 elite ultra-marathoners and Ironman distance athletes perform a maximal graded exercise test and a 3-hour submaximal run at around 60 percent of VO2 max on a treadmill to assess metabolic responses.

During the experiment, Group I was fed the classic high-carb diet, whereas Group II was given a low-carb diet for an average of 20 months. The result? The researchers concluded that long-term keto-adaptation results in drastically high-fat oxidation rates.

Additional resource – 30 Keto recipes 

The Case of Zach Bitter

Now, let’s talk about Zach Bitter, the legendary ultra-marathoner who holds the American record for running 100 miles. He’s been surfing the keto wave since 2011 and cycles between ketosis and low-carb.

What’s more? He focuses on ultramarathons, which are run at a slow and steady pace, making fueling with fat more sensible.

However, it’s important to note that the more intense the race, the more you’ll need carbohydrates instead of fat for fuel.

You can hear him talk about his keto experience on the Lex Friedman podcast:

Note – as I mentioned earlier, full-fat adaption may take up to two to three months. This is when the body uses fat as its primary energy source. However, most of the research I found did not last this long, leaving many questions about whether the subjects were fully fat-adapted, whether their ketone levels were measured, or whether they were in ketosis.

Can you Train For A Marathon While On Keto?

Of course, the answer is yes. You just have to do it the right way.

If you’re willing to invest enough time and effort to make fat your main macronutrient and fuel source, you can train and run a marathon on keto.

How long it will take you when you’re newly on keto depends on you, but according to most experts, it can take months.

What’s more?

Some people may never seem to become completely fat-adapted while eating keto. If that’s your case, consider trying carb-cycling or switching from keto to low-carb eating during heavy training days.

Keto Marathon Training Tips

Before you toe the line of a marathon race on keto, there are a few things to consider.

These include:

  • Your ketosis length. The first thing to consider is how long you have been in this metabolic state. In most cases, when you’re new to the keto diet, you’ll find it hard to muster up the energy needed for distance running at your pre-keto pace and speed.
  • Your calories. You cannot stay in ketosis while eating low-fat. That’s the rule. Your body is primarily fueled by fat on the keto diet, so not meeting your calorie needs means you don’t have enough fuel in the tank.
  • Your fat intake. Serious about making fat your main source of fuel? Then your diet must reflect that intention. Simply increasing your protein intake won’t do the trick. If you don’t fuel your body with enough healthy fat, you won’t be able to power through those long workouts.
  • Carbo cycling. Consider adding a few low-glycemic index carbs during heavy training days to ensure you have enough fuel in the tank. Remember that to stay in ketosis, you’ll need to stay under 40 to 60 net carbs per day, depending on your metabolism and training volume.

And that’s all!

Additional Resources

Here’s your guide to the Yasso 800 Workout

How to qualify for the Boston Marathon

Keto Marathon Training – Conclusion

If you’ve been keto-adapted for a while and it’s working well for you, then nothing should be stopping you from running a marathon on a keto diet.

I won’t recommend trying the keto diet in the last few weeks leading your marathon.

Think long-term.

Three to four months is a good time range.

Transitioning from eating more fat to fewer carbs takes time for your body to adjust.

That’s why the off-season is the perfect time to transition to a keto diet—or at least when you’re not training for a specific race when you don’t have any race on the schedule soon.

Once you find out what works the best for you, you can start to train for races on a keto diet.

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