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Running on Keto; Affects of the Keto Diet on Runners

on October 15, 2021
Running on Keto  The Affects of the Keto Diet on Runners


Running on Keto, of all the diet fads, the one that is based on legitimate science and generally accepted as a lifestyle, the Ketogenic Diet, or Keto, appears to be here to stay. Touted as an ideal way to lose excess body fat, improve chronic heath issues and clear up skin conditions, the keto lifestyle has piqued the interest of athletes everywhere. However, is this the optimal diet for stereotypical carbohydrate-loving runners?

What is the Keto Diet?

In a nutshell, the keto diet is simply a way of eating that forces the body to burn fat—instead of carbohydrates—for fuel. Carbohydrates are broken down to glucose in the body, and glucose is the body’s most accessible form of energy. Consider how an energy gel pack almost immediately refuels the runner mid-race, and it’s easy to see how quickly the body converts carbohydrates to energy.

For the body to burn fat before carbohydrates for fuel, the level of fats ingested must be increased while the level of carbohydrates ingested must be decreased. The keto dieter will generally get 80% of their calories from healthy fats, 15% from proteins and 5% from complex carbohydrates. These macronutrients, or macros, can come in the form of fatty fish, lean meats, eggs, dairy, green vegetables, oils and whole grains.

Why Burn fat for Fuel?

To burn fat for fuel the body must be in ketosis. This happens regularly when glucose stores are depleted and fat reserves are tapped for energy like with extreme distance running in ultra-marathons. The purpose of the keto diet is to keep the body continually in the state of ketosis, or the metabolic state of using ketones released by fat cells for fuel instead of glucose.

Why would a runner want to be in ketosis? There are many reasons keto and running would seem to go hand-in-hand. For one thing, fat molecules release 125% more energy than carbohydrate molecules when burned. Fat molecules are also much more plentiful in the body. In comparison to a car running on gasoline, the body gets the most miles to the gallon by running on fat.

Fat is a longer-lasting fuel for the body. Carbohydrates act as the body’s igniter, or fire-starter. They both light up quickly but burn out just as quickly. Whereas fats burn slow and steady. In the body, this translates to sustained energy and increased satiety between meals. Hangry happens, but not as often in ketosis.

How a Keto Diet Affects Runners

Though there have been few studies on the long-term fat adaptation of the keto diet, we can glean some knowledge about running on keto in the short-term. This study published in the Journal of International Society of Sports Nutrition followed five endurance athletes over 10 weeks. Some positive outcomes of the study include:

  • participants all saw a reduction in body weight
  • after an initial reduction in energy, energy levels returned higher than normal during exercise
  • inflammation was reduced
  • improved recovery time

On the other hand, some negative outcomes from the study include:

  • participants’ average times to exhaustion decreased by about two minutes
  • high-intensity workouts were more difficult
  • overall reduction in maximum aerobic performance (speed and power)

Another study covered the submaximal exercise capacity of runners on a keto diet and runners on their regular diets. It found no changes in those participating at 60% or less VO2 max, or low-intensity running, but those participating at over 70% VO2 max, or high-intensity running, endurance and speed declined on a keto diet.

It should be noted that to be fully fat-adapted, where the body is using fat as its primary fuel source, can take up to 12 weeks. Many studies do not last this long, leaving questions as to whether runners were fully fat-adapted, if they were in ketosis and whether keytone measurements were taken.

Keto and Running: Can they Coincide?

What does this all mean for runners considering a keto lifestyle? Ultra-runners, those who run great distances—30 miles or more in single races—are most inclined to benefit from a keto diet. Since ultra-runners are often entering into ketosis during their lower-intensity but longer runs, a keto diet makes that conversion easier.

Leisure runners who may not be concerned with racing or PRs can also benefit from a low-carbohydrate keto diet if they rarely participate in high-intensity workouts. They may enjoy an enhanced body composition, feeling fuller between meals and less inflammation.

High-intensity runners concerned with increasing speed or hitting a new PR may not want to try a full keto diet since it has been shown to decrease speed and power. These runners might also find that a keto diet does not supply enough energy for their intensity level.

If a higher-intensity runner is interested in running on keto for all the other health benefits, he or she could consider a variation on it. Some athletes can consume carbohydrates prior to a big race without removing themselves from ketosis. They would simply need to ensure they have burned most of the carbohydrates consumed. This gives them the appropriate fuel for their intensity level without affecting their diets.

Give Keto Running a Try

If you are considering running on a keto diet, we invite you to try a virtual 5k or virtual challenge. Since these races can be run on your own time, it gives you the freedom to determine if a keto diet will work with your running routine without the formalities and expense of prepping for a live race.

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