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Running On A Ketogenic Diet: Are There Any Risks?

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Running and keto: peanut butter and jelly or oil and water? That depends on who you ask. The Keto diet restricts carbs and amps up your fat intake (abbreviated to LCHF). By cutting out carbs and adding more fat, you send your body into a state of ketosis that burns fat to help you lose weight. 

While entering into ketosis will give you plenty of energy to get you through the day while burning unwanted fat (hello weight loss!), it’s generally not ideal when training for a race or setting particular running goals. 

You technically can run while in ketosis but expect your performance to suffer slightly. Recreational runners found that this diet helped energize them for a run, but runners that wanted to smash PRs found that their performance suffered. 

So, is keto and running right for you? Let’s dive in. 

How does the Keto Diet Work? 

To understand how this high-fat diet affects your running, we first must understand how this diet works. The Ketogenic diet boils down to low carb intake and high fat intake.

By restricting your carbohydrate intake, your body will reach for the next available fuel source: fat. When you enter into ketosis, your body burns fat more efficiently and boosts energy levels by burning fat into ketones in the liver. 

When in ketosis, you earn higher mental clarity while your body burns through all of that excess fat. It’s great for weight loss and pairs well with a modest running schedule. If your ultimate goal is to lose weight and get in shape, the Keto diet is worth checking out. 

The Keto Flu

The Keto flu has no medical documentation, only anecdotal evidence. If you have talked to someone that has tried the Keto diet, they will likely warn you of the Keto flu. 

These symptoms, including fatigue, headache, difficulty sleeping, irritability, brain fog, and nausea, often hit around the 2-7 day mark. These symptoms are often an indication of your body adjusting to the new diet and are not cause for alarm. 

When experiencing the Keto flu, it’s best to keep your exercise to a minimum, which means hanging up your running shoes as you ride it out. Most keto dieters kick their symptoms in about a week. 

After your symptoms disappear, it’s time to lace up those running shoes to go for a run!

Keto and Running

I know what you are thinking: how can a low-carb diet be suitable for running? Carbs, after all, are the primary fuel source for runners. How will you have enough fuel to get you through the end of your high intensity run by restricting your carb intake? 

For recreational runners, entering into ketosis doesn’t make much of an impact. You still have all of the fuel in your body to get you through a nice and easy run while you burn fat. Many runners that train at a modest intensity saw no noticeable difference in their performance. 

If your primary running goal is to lose weight and boost your overall health, the Keto diet is the way to go. However, if you are training for a race or looking to smash a PR, keep a few things in mind. 

Keto and Running Performance

Can you run while in ketosis? Yes. Will your performance suffer? Also yes. Distance runners and endurance athletes that wanted to boost their distance or speed for marathons and ultramarathons found that their overall performance suffered up to 5 percent. 

In one study, it was also noted that VO2 max levels suffered when entering into ketosis. In other words, this means that your body cannot utilize as much oxygen when engaging in aerobic activities. A lowered VO2 max translates to diminished endurance. 

While the fat-adapted Keto diet has its merits, it’s generally not recommended when training for a race. Decreased performance means that you won’t be able to tap into carbohydrates to run for long distances at faster speeds or need quick bursts of energy. 

If you plan on giving the Keto diet a try, I recommend trying it out in the off-season. 


A fierce debate rages in the runner world about whether it’s ideal for running on the Keto diet. Studies have shown that significantly restricting carbs from your diet shows no indications of improved performance and can even hinder your overall performance. 

For serious runners that are training for a marathon/half marathon or just want to increase performance over time, the Keto diet may not be your best option. 

If your daily runs and intensity workouts suffer due to excess weight, the Keto diet may be worth considering. By eliminating carbs as a source of fuel and entering ketosis, you will efficiently burn body fat quickly – that translates to pounds lost on the scale. 

When you couple this diet with moderate cardiovascular exercise that doesn’t demand high bursts of energy, you can expect that excess body weight to melt away. For many, running and Keto are the perfect pairing for weight loss. 

If you are still on the fence, giving the Keto diet a try won’t hurt. If you find that it’s simply too hard to maintain, or your body just doesn’t respond to this diet in the way you had hoped, add carbs back into your diet!

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