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Food & Nutrition

The Rundown on the Keto Diet for Runners

by On Jun 14, 2021

Is a Keto diet good for runners?

The Rundown on the Keto Diet for Runners

With the increasing popularity of the ketogenic diet in the athlete community, you must be wondering if there are benefits to jump on the bandwagon. The answer to whether the diet can benefit you depends on your goals.

If your goal is to burn fat for a better physique, a keto diet could help. But before you go and throw out all your rice and fruits: if your goal is faster running performance, a keto diet worsens performance compared to a high-carb diet.

To understand why, let’s delve into what a ketogenic diet is and what it does to our body.

The low-carb high-fat ketogenic diet encourages less than 10% of calories to come from carbohydrate, and 70% from fat.

This is vastly different from the usual high-carbohydrate, low-fat dietary guidelines for athletes, with 40-65% of calories from carbohydrates, and 20-35% from fat. 

How does the keto diet affect exercise? 

The type of exercise determines what fuel our body utilizes. Low intensity exercise, like a leisurely walk or run for 30 minutes, uses mostly fat, and a bit of carbohydrate as fuel.

High intensity exercises, like sprinting or shuttle runs, on the other hand, use carbohydrates as the main fuel tank. Low-carb diets are therefore less suited for high intensity activity like running, but may be helpful for lower intensity exercises instead. 

The Rundown on the Keto Diet for Runners
Photo Credit: 123RF

At moderate intensity workouts, whether fat or carbohydrate is the main fuel source depends on the individual athlete’s adaptations. Over time, an athlete can train themselves to be better at oxidizing (using) fats as energy and rely less on carbohydrate, by going on a low-carb diet

So you might think, endurance exercise may benefit from the keto diet? Because improving the metabolic use of fats during exercise (rather than the limited amount of carbohydrates when you can't eat/take carbs) theoretically improves this.

Indeed, the keto diet has helps reduce fatigue when doing low intensity exercise, but at a slower pace. Most endurance athletes are looking for a boost in performance, rather than to just ‘keep going’ though. 

A renowned sports dietitian, Burke, tested the effects of a ketogenic diet vs high carb diet in female race walkers over 4 weeks. They found that the high-carb diet helped improve performance by 134 seconds in 10k and 20k races, but slowed in ketogenic diet by 61 seconds.

Cycling and sprinting performance was also reduced when athletes are on a keto diet. These studies were done on athletes who followed the ketogenic diet for 4 weeks. Some proponents argue that it takes much longer to be fat adapted, so the jury’s still out on its effects, if you have been in ketosis for a long time. 

Just as well, some research has shown that the keto diet may to reduce bone strength in athletes over a 3.5 week period, with concerns that long-term use of this diet could increase risk of bone injuries in high performance sports. 

So is a keto diet out of the question?

Not necessarily. When you're having an off season or a long period of light training as a break, using a ketogenic diet can be helpful to maintain weight or reduce fat ratio to improve your body composition for competing.

But as the keto diet can tend to increase the body’s need for electrolytes like sodium, potassium and magnesium, ensure you are having adequate amounts of these either in the form of supplementation or foods rich in these if you are experiencing signs of deficiency

Alternatively, the ketogenic diet may be the choice if you’re a recreational athlete where heightened performance of a few seconds doesn’t matter, and you’re trying to maintain a leaner physique or reap the metabolic health benefits of a ketogenic diet. 

To keto or not to keto?

If your overall goal is to improve endurance performance, research shows the traditional high-carb, low-fat diet is better. But there’s no one-size fits all approach, and every athlete will have their own individual preferences. Based on the research, it’s likely that - unless you are well-adapted on fat metabolism - you’ll benefit from a higher carb intake on heavy training days, whilst reducing carbs on rest days.

Anecdotally, we know that athletes like Zach Bitter have broken endurance world records and cyclist Chris Froome won the Tour de France while on a keto diet. Constant, the founder at Ketomei, lost 10kg within 6 months of following the keto diet and says that he can “power through my weekly runs and with much greater mental clarity”. 

If you are keen to run a marathon on the keto diet, there’s great advice out there from others who have done it. Ultimately, everyone is different with individual fuel needs based on factors like body composition, your genetics, and how long you’ve been adapted.

If you have any concerns, make sure you speak to a doctor before you start any kind of diet and together they may be able to discuss the best training plan for you.

Until then, perhaps there’s no need to throw out all packs of rice just yet, but neither is it healthy to go crazy on the sugar-laden energy drinks for the average runner! 

Bonnie Lau is an Australian-trained dietitian with almost 4 years experience. She has worked at SGH and TTSH prior to joining Holmusk. She believes in the empowerment of clients to take greater control of their own health and achieve nutritional goals. She loves food and is passionate about balancing health and enjoying Singapore’s amazing food scene.

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