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Keto For Athletes: Getting Ready for 2019 Los Angeles Marathon

Published on: February 27, 2019

Keto For Athletes: Getting Ready for 2019 Los Angeles Marathon

Some misconceptions surrounding keto for athletes might have you wondering if it’s a good idea to be on the keto diet when you’re preparing for the 2019 marathon. We’re going to clear those and show you how the ketogenic diet can help you perform better.

Keto for Athletes Misconceptions

High carb is needed to maintain performance

It’s a well-known fact that you need to eat a good nutritious diet to perform great in physical activities. For decades, we’ve been told that a high carb diet is the best approach to perform better in sports and muscle building. This is why we’re used to seeing people sip on glucose energy drinks at sports events and the gym.

An article published by the British Journal of Sports Medicine states athletes should consume about 30-60 grams of carbs per hour during exercise [1].

Here are the three main reasons why a high carb diet is considered to be the best for athletic performance:

1. Glucose is the primary fuel that our brain uses for energy, and when you eat a high carb diet, the carbs in your food is digested and stored in the liver and muscles to be used as an energy source.

2. Prevents the symptoms of hypoglycemia such as fatigue, dizziness, nausea, and muscle weakness.

3. To fill up glycogen storage to be used as fuel during your performance time.

So the truth is that a high carb diet is beneficial for athletes, the misconception, however, is that a high carb diet is the only way you can perform better during sports and exercise.

There’s strong emerging evidence to support that low carb diets can enhance athletic performance.

For instance, a research paper published by the European Journal of Sports Science states that ketones as a primary fuel source when carbs are limited could be beneficial for athletes [2].

A 2015 study found that elite endurance athletes who ate high fat, low carb diet burned twice as much fat compared to the athletes who ate a high carb diet. In this study, ten low carb athletes ate a ketogenic diet consisting of 70% fat, 19% protein, and 10% carbs. And ten high carb athletes most of their calories from carbs (59% carbs).

They found out that not only did the low carb athletes burn twice as much fat, but they also had normal muscle glycogen levels [3].

Ketosis decreases performance

When your carb levels are below 50 grams per day, your body will use stored glucose (glycogen) for energy, and when glycogen deplete, your body will enter a metabolic process called ketogenesis.

During this process, fatty acids are metabolized into ketones to be used as an alternative fuel source. The metabolic state of your body using ketones for energy is called ketosis [4].

Those who believe high carb diets are the best nutritional approach for physical performance also think that ketosis can do the opposite and slow you down.

That is not true, and in fact, ketone bodies have been found to produce more ATP for energy than glucose.

A 2018 study found that keto-adaptation helped endurance athletes to perform better than high carb athletes [5]. In this study, 22 male endurance athletes completed high-intensity training for 12 weeks while being on a high carb diet or a low carb ketogenic diet.

Results revealed that compared to high carb diet, low carb keto diet enhanced body composition, fat oxidation, and performance during exercise.

Too much fat intake can slow you down

This is another misconception that too much fat intake can slow down performance. You can see how that’s not the case in the studies discussed above.

For instance, Zach Bitter, an award-winning ultra-marathoner and coach has been eating a ketogenic diet consisting of at least 70% healthy fats since 2011. He says, “Whether or not I’m training, the piece that stays consistent in my diet is using fat as a primary micronutrient.”


Can Runners Do the Keto Diet?

Zach Bitter (discussed above) is a perfect example to show that the keto diet can work for runners. His view on the ketogenic diet matches with the results from the study discussed above. Keto diet has been found to burn more fat than high carb diets, which means once you become fat adapted, your body can instantly use fat for fuel than waiting for carbs to be turned into glucose for energy.

Another thing is that glycogen levels can deplete faster and place pressure on athletes to eat high carb foods at certain times before, during, and after the exercise. On the other hand, when you’re in ketosis, you’re already burning fat for fuel which means fat will always be readily available to be used as an energy source.

One of the greatest evidence-backed benefits of the ketogenic diet is that it can help improve cognitive performance and this is also beneficial for runners as the keto diet can help them focus and think clearly [6].

Can You Do Cardio on a Keto Diet?

Cardio is fine on a keto diet, especially after you become fat adapted. As discussed earlier, the ketogenic diet has been found to burn more fat than a high carb diet. Aerobic exercises such as running and biking can help increase fat oxidation which makes them keto friendly. You may also feel less hungry after doing cardio on a keto diet than you would on a high carb diet.

Benefits of Keto for Athletes

Here are some of the benefits of keto for athletes:

Increased cognitive performance

As discussed earlier, the ketogenic diet has been found to improve cognitive performance which means athletes may have less brain fog and more mental clarity to perform.

For instance, a 2010 study found that diet-induced ketosis improved cognitive performance in aged rats. In this study, the rats were exposed to hypobaric hypoxia after being fed a standard or a ketogenic diet for three weeks. Results revealed that keto diet cognitive performance in the aged rats under normoxic and hypoxic conditions [7].

In another 2012 study, 23 older adults with mild cognitive impairment were assigned to either a high carb or ketogenic diet for six weeks. Results showed improved memory in the keto group, and the study concluded that even a short term implementation of the keto diet could improve memory function in those with an increased risk of Alzheimer's [8].

Appetite control

Since the keto diet is a high-fat diet, it can make you feel fuller for longer. You’ll also be using fat for fuel instead of glucose which means the chances of experiencing hunger symptoms during training sessions are less on the keto diet.

Increased energy

When you’re on a ketogenic diet, you’re already burning fat for fuel which means you won’t be “hitting the wall” as you would after the glycogen storage deplete on a high carb diet. This is a huge benefit for endurance athletes, and another plus is that ketones have been found to produce more energy than glucose.

Better mood

Keto diet can help reduce the tiredness, or the “sugar crash” symptoms you may have experience on a high carb diet [9]. Keto diet has been found to reduce stress and anxiety. Thus it enhances your mood when you’re working out.

Reduced muscle loss

Studies have shown that a keto diet can help lose body fat without having any negative impact on the muscles. This means athletes on the keto diet can work out freely without worrying about muscle loss.

Muscle building

Keto diet can also help you build muscles which can help enhance athletic performance.

How to Prepare for a Marathon While on Keto

Plan well ahead

It’s not a good idea to start the ketogenic diet a day or a week before your marathon day. Your chances of experiencing carb withdrawal and keto flu symptoms are higher when you’re starting.

Thus you need to give your body plenty of time to get used to the diet first. You may want to start by lowering your carb intake while simultaneously increasing your healthy fat intake.


Replenish your electrolytes

Since the ketogenic diet is diuretic, you’ll be losing a lot of electrolytes via urine and sweat, and you’ll be losing a lot more if you happen to be an athlete or someone who works out a lot. This may result in keto flu symptoms such as fatigue, muscle weakness and cramps, brain fog, dizziness, and more.

Keto flu symptoms are the last thing you’d want to experience when you’re preparing for a marathon so be sure to replenish them every day. Saltwater, pickle, avocado, bone broth, and coconut water are excellent sources of electrolytes. Perhaps you might want to carry a small bottle of sea salt water when you’re training and sip it a few times between each session.

Become fat adapted

You will be able to enter ketosis within a week of starting the keto diet; however, it may take several weeks to months to become fully fat adapted. It’s easier to reach fat oxidation when you become fat adapted because your body can utilize fat for fuel.


MCT oil supplement is an excellent source of instant energy and ketones boost. Unlike long-chain triglycerides, medium chain triglycerides don’t have to be broken down by bile enzyme before being absorbed by the liver for energy. Pure MCT oil has many health benefits such as improved energy, cognitive performance, and satiety. One of the best ways to incorporate MCT oil in your diet is by adding it to your morning shake or smoothie.

Do not however exceed the recommended dosage of 2 tbsp per day and it’s best to start with 1-2 tsp per day for a week and then gradually increase.


For decades, high carb diets have been praised and preached as the best nutritional approach for athletes. However, there’s strong emerging evidence to support the theory that low carb and high-fat diets like the ketogenic diet can enhance exercise performance without any adverse effects.

As discussed earlier, the keto diet can be beneficial for marathon runners and has excellent benefits such as improved energy, focus, and performance. However, it may not be a good idea to start the diet a day or a week before your big day. Consider giving yourself at least a month or two in advance to become fat adapted first.

And don’t forget to replenish your electrolytes as failing to do so can have adverse effects, especially for athletes and those who perform high-intensity workouts.


  1. Hassapidou M. Carbohydrate requirements of elite athletes. 2011 January -
  2. Volek JS, Noakes T, Phinney SD. Rethinking fat as a fuel for endurance exercise. 2015 -
  3. Volek JS et al. Metabolic characteristics of keto-adapted ultra-endurance runners. 2016 March -
  4. Masood W, Uppaluri KR. Ketogenic Diet. 2018 October -
  5. McSwiney FT et al. Keto-adaptation enhances exercise performance and body composition responses to training in endurance athletes. 2018 April -
  6. Ota M et al. Effect of a ketogenic meal on cognitive function in elderly adults: potential for cognitive enhancement. 2016 October -
  7. Xu K et al. Diet-induced ketosis improves cognitive performance in aged rats. 2010 -
  8. Krikorian R et al. Dietary ketosis enhances memory in mild cognitive impairment. 2012 February -
  9. Huang Q et al. An 8-Week, Low Carbohydrate, High Fat, Ketogenic Diet Enhanced Exhaustive Exercise Capacity in Mice Part 2: Effect on Fatigue Recovery, Post-Exercise Biomarkers and Anti-Oxidation Capacity. 2018 October -

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