Is Going Keto the Right Choice for Runners?

The ketogenic diet has been popular for several years, as it has been praised for restricting carbohydrates and increasing fat intake, usually in the name of weight loss.

If you’re looking to change your eating habits this year, you might be wondering if the Keto diet is right for you and if it can improve your running performance?

To get to the bottom of the pros and cons of the keto diet for runners, we spoke to dietitians to get the full scoop. Here’s what you need to know before you swap all carbs for all fats.

What is the keto diet?

The ketogenic diet (or keto diet) sets very strict guidelines for cutting down your macronutrient intake (carbs, proteins, and fats). Those following keto consume 80 percent of their calories from fat, 15 percent from protein, and 5 percent of calories from carbohydrates—the fuel source your body and brain prefer to tap first because it’s the fastest and easiest to access.

Key ingredients of the Keto diet include fish, meat, eggs, dairy products, oils and green vegetables. Even healthy, complex carbohydrates such as whole wheat pasta, rice, potatoes and fruit are off limits.

Here’s how the keto diet works: When your body no longer has access to fuel from carbohydrates – either because they’ve been cut from your diet or you haven’t eaten in a long time – it enters a state called ketosis. That means your body looks for the next best fuel source: fat. And it uses the available fatty acids to produce a substance called ketones. Therefore, people who are in ketosis and eat more fat will burn more fat.

The ketogenic diet should not be confused with a low-carb, high-fat diet, which is similar. The difference is that the keto diet aims to increase ketone levels in your blood, which puts your body into ketosis.

What are the benefits of the keto diet?

While our body prefers to feed on carbohydrates, ketones can actually fuels the brain and body, says Lizzie Kasparek, RD, a sports dietitian at the Sanford Sports Science Institute. So it is not the case that you exhaust your body in a dangerous way.

“Being in ketosis does not mean that muscle glycogen levels drop. Over time, the keto-adapted athlete can improve his or her ability to burn fat for fuel and still have glycogen available,” says Kenneth Ford, Ph.D., director and CEO of the Institute for Human and Machine Cognition. (As long as the athlete’s carbs are loaded.)

Whether runners in particular should put their bodies into a state of ketosis depends on your goals – and the verdict is still out on whether it actually helps performance. Most studies on keto and athletes involve only a small number of participants, and most researchers say we need more studies on this topic.

This is evident from a small study among five endurance athletes, published in the Journal of the International Society of Sports Nutrition, showed that a 10-week keto diet improved athletes’ body composition and well-being, but not their performance. In fact, the athletes initially experienced reduced energy levels and an inability to do high-intensity exercise.

Another small study in the journal Medicine and science in sport and exercise looked at the effects of the keto diet on training efficiency in eight trained athletes. After following the diet, the athletes saw a decrease in running speed and strength; the walking speed at VO2max decreased by 5 percent.

Other research, including a review of seven articles on the topic, says there are limited findings on the benefits of keto for endurance athletes and results are mixed when it comes to VO2 max and other performance results.

What are the disadvantages of the keto diet?

“There’s not really a lot of good research showing that these people can perform better, and that’s really what runners care about,” says Kasparek.

Ford also points out that in the studies on ketosis and performance with negative results, the athletes are often not sufficiently fat adapted (when the body is trained to tap into fat stores for energy, which can take several months) or even in ketosis are. making it difficult to truly gauge whether the diet is effective when it comes to performance. Performance also typically involves an athlete training at a relatively high intensity, with carbohydrates being the main source of fuel.

Runners who may benefit from fat adaptation are those who run long distances, such as ultramarathons. Once you rack up those later miles, your body relies on fat for energy production.

For everyone else, carbs are probably still the best choice, especially if you’re running at a higher intensity than if you were running 50 miles. Running at a lower intensity allows your body to burn fat for fuel, Kasparek explains. “But because carbohydrates are the main source of fuel at higher intensities, you may be sacrificing important workouts or your race to follow a certain diet,” she says.

What should you know before trying the keto diet?

So, does the keto diet work and should you try it? The bottom line: When done right, runners who need to tap into fat stores for long distances can benefit from occasionally eating fewer carbs and relatively more fat during longer, less intense training sessions. A runner doesn’t necessarily have to be in ketosis to follow this type of “carb periodization.”

Runners who do speed workouts or who enjoy shorter distances at higher speeds or who incorporate high-intensity workouts into their training are still better off if they eat a healthy, balanced diet that includes carbohydrates.

To lose weight, Kasparek says, it’s possible to lose weight by modifying a normal diet, such as adding more healthy fat or cutting out processed foods. (And focus on a calorie deficit.) But there’s more than one way to lose weight, and one banana won’t stop you—we promise.

Heather is the former food and nutrition editor of Runner’s World, the author of The Runner’s World Vegetarian Cookbook, and a seven-time marathoner with a best of 3:31, but she is most proud of her 1:32 half, 19:40 5K and 5:33 miles. Her work has appeared in The Boston Globe, Popular Mechanics, The Wall Street Journal Buy Side, Forbes Vetted, Cooking Light, CNN, Glamour, The Associated Press and

Portrait photo of Namrita Brooke, Ph.D., RDN

Dr. Namrita Brooke is a full-time endurance sports coach and sports nutritionist who advises active individuals and amateurs to professional athletes. She is also an adjunct professor in the Department of Kinesiology and Health at the University of West Florida. Professionally, she also serves on the Editorial Board of the Sports Nutrition Care Manual and remains involved in nutrition and exercise research, student mentoring and coach development. Namrita’s personal athletic experience ranges from ultra-endurance mountain biking to off-road triathlon, cross-country mountain biking, gravel biking, duathlon, cyclocross, running and trail running. Her research background includes research into hydration and sports drinks, and the interaction between diet, physical activity and the brain.

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