Should Endurance Athletes Try The Ketogenic Diet?

Greenletes / Sports Nutrition / Diets and weight loss / Should Endurance Athletes Try The Ketogenic Diet?

Last updated on June 15th, 2021 at 09:56 am

The keto diet may help manage appetite and result in weight loss, but it can severely impair athletic performance. Here’s what you need to know before eating a high-fat diet.

Maybe you’ve heard of a friend or fellow athlete who tried the keto diet and loved it. Although the keto diet has become popular among those looking to lose weight, many endurance athletes are trying the keto diet in the hopes of better performance.

Is the keto diet good for endurance athletes?

Although it’s well proven that carbohydrates are the main fuel source for energy, some believe that it’s possible to train the body to use fat as fuel.

But before you hop on the keto bandwagon and start filling your plate with fatty foods and drastically limiting your carbs, find out if this eating plan is right for you.

What is the Ketogenic Diet?

Believe it or not, the keto diet has actually been used in clinical settings as treatment for epilepsy (seizures). The Ketogenic diet is a high fat, moderate protein and low carb diet– roughly 70-80% of calories from fat, 10-20% from protein, and a mere 5-10% from carbs.

After eating a  high fat and low carb diet for at least 7-10 days, the body start to produce ketone (fat) molecules. When the body starts to use ketones as fuel for everyday activities and exercise, this is known as ketosis.

In addition to weight loss, proponents of the keto diet claim that you’ll experience increased energy levels and enhanced physical and mental performance.

In order to eat such a high level of fat and low level of carbs, you’ll need to eliminate a wide variety of plant-based foods, including all grains (even whole grains), fruit, starchy vegetables, legumes and sugar.

And you can expect to fill your plate with plenty of meat, leafy greens and other non-starchy veggies, high fat-dairy (cream and butter), nuts and seeds, avocado, butter, oils and high-fat salad dressings. Only low-carb zero-calorie sweeteners, such as stevia, erythritol and monk fruit, are allowed.

What happens when you try keto?

If drastically limiting your food choices sounds doable, you should also be aware of some of the side effects that come along with following this plan.

During the first 5-7 days of keto eating, you may experience the “keto flu”, otherwise known as carb withdrawal. This “flu” is accompanied by feelings of nausea, fatigue, headaches, and just overall crappiness.

In addition, the build up of ketones in the body creates acetone, which can make your breath smell sour. Don’t get too close to anyone while talking!

Lastly, since the diet is low in fruits, vegetables, beans and legumes, it’s also low in fiber. That means you may experience constipation. If so, drink plenty of water and try a fiber supplement.

All of these side effects aside, there is research to suggest that the keto diet may make you feel less hungry and result in weight loss.

Should endurance athletes try a keto diet?

As an athlete, you’ve heard a lot about how carbohydrates are a necessary fuel source, so should you even consider giving keto a try? I’m not going to sugar coat this—I don’t recommend the keto diet for people who engage in endurance sports. There, I said it.

For high intensity exercises, such as running, cycling, boxing, swimming, etc., the body requires quick-acting energy from carbohydrates. Specifically, the body uses two forms of carbs—glycogen stored in the muscles and liver and dietary carbs. [Related: 11 Healthy Carbs For Athletes]

Is the keto diet good for endurance athletes?

During the first 30 minutes of exercise, the body taps into glycogen stores for energy and then it uses any carbs you ate to power you through longer than that. Proponents of the keto diet argue that the body can only store a finite number of carbs, and that is true. For any exercise lasting longer than an hour, you have to take in carbs to avoid hitting the wall.

The body can store more fat than carbs, but using fat as fuel is an inefficient and taxing process. Some endurance athletes believe that they can train their body to use fat more efficiently than carbs, but the research on this claim is limited.

 As a matter of fact, a study in Nutrition & Metabolism suggests that following a ketogenic diet may actually hinder athletic performance. Without enough carbs in the body, you may find yourself struggling during workouts.

The other aspect to consider is that the keto diet may lead to a decrease in appetite. While this may sound great, you may struggle to meet your daily calorie needs necessary for training. Plus, with very little fruits and vegetables in the diet, you may experience vitamin and mineral deficiencies that can lead to injury.

One positive aspect of keto is that the plan’s minimal amount of fiber might benefit endurance athletes with an overly active digestive system.

Is keto good for strength training?

If your primary goal is building muscle mass, this plan will likely fall on the amount of protein you need to build muscle. [Related: 10+ Best Recovery Foods For Vegetarian Athletes]

That said, the body uses fat as fuel during lower intensity and longer duration exercise, like a lift session. One study suggests that following a keto diet while resistance training may decrease fat mass, but it does not increase muscle mass.

is the keto diet beneficial for strength training?

In other words, if weight loss is your primary objective to help you achieve your fitness goals, keto may help get you there faster. But if you’re already slim and want to put on muscle mass, keto probably won’t help.

What about Keto 2.0?

Since strictly following the original Keto plan is not easy, followers have since started to adopt Keto 2.0. In this version, about 50% of your calories come from fat, 30% from protein and 20% from carbs. This is roughly twice the amount of carbs you’re allowed on the original version so your body is no longer in ketosis in keto 2.0.

This version also focuses on eating more fruits, vegetables, beans, complex whole grains, lean proteins and less saturated fat, which is a good thing. By eating more of these foods you’ll also naturally take in more fiber, which can help keep your digestive system regular and lower disease risk.

Just be sure to get those extra grams of carbs from good sources. While the keto diet still has it’s drawbacks, keto 2.0 is much more sustainable and a better choice for most athletes.

An RD’s take on the keto diet for athletes

As I said, I don’t recommend the keto diet to athletes, especially those who follow a vegetarian or vegan diet. It’s very difficult to follow, not all that sustainable and may actually hinder performance.

That said, if you do want to try the keto diet, keep these in mind that you really need to love the taste of fatty foods. For plant-based athletes, that means a diet that is mostly avocados, oil, nuts, seeds, cream and butter.


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I’m Natalie Rizzo, an NYC-based Registered Dietitian.

My mission is to help everyday athletes fuel their fitness with plants.

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