Sunday, March 8, 2020

Can The Ketogenic Diet Help With Weight Loss And Sporting Performance?

Picture from The Star
I couldn't believe my eyes when I saw two of my patients two days ago (both husband and wife are in their 50's). Both had lost 12-15 kg while on a ketogenic diet supplemented by going to the gym occasionally in less than three months. The husband even showed me a six-pack for his abdominal muscles. He said that he hadn't had them since his teenage years. I was shocked to say the least.

It seems like the ketogenic diet (eliminating carbohydrates) is all the rage in the fitness world nowadays. The ketogenic diet is similar to the caveman diet I've written about way back in 2009. It is probably time for me to revisit that low carb, high fat diet since I get questions on whether it is a good to be on a keto diet? Whether it helps to lose weight and most importantly whether it makes you stronger or faster as an athlete?

Those on the ketogenic diet follow a strict guideline to consume 80 percent of their calories from fat, 15 percent from protein and just 5 percent from carbohydrates.

After you eliminate carbs from your diet, your body goes into a state of ketosis where it uses fat for fuel. It uses the available fatty acids to produce ketones such that when your body is in ketosis, eating more fat will enable you to burn more fat.

While it is clear that you can definitely lose weight (or fat) while on the ketogenic diet, I am more interested if it helps sporting performance.

Previously I had questioned if carbohydrate loading was still relevant. The 1983 article quoted in that post is frequently quoted in the ketogenic community. The cyclists in that study underwent a 4 week ketogenic diet showed they used significantly more fat compared to a high carbohydrate diet.

Yes, fat burning was significantly ramped up (since they had 4 weeks to get used to the diet), time trialing ability remained unchanged but high intensity power was affected. There was a severe restriction on the ability of the cyclists to do anaerobic work.

Sports scientists around the world subsequently experimented with various fat adaptation protocols and kept coming up with same problem. The ability to sustain race pace was not a problem but sprint ability was always compromised.

Louise Burke, head of Sports Nutrition at the Australian Institute of Sport got together 19 elite 50 km race walkers preparing for the 2016 Rio Olympics over two training camps. They spent 3 weeks adapting to a low carb, high fat diet as the 1983 Phinney study had prescribed. Results confirmed that these elite walkers became super efficient at fat burning. The bad news was these fat adapted walkers became less efficient, requiring more oxygen to sustain their pace. This is a big liability while racing.

Consider an elite runner in the Boston marathon when a fellow runner surges on Heartbreak hill and he/ she cannot follow, the race may then be lost. Or for a cyclist (who on a low carb, high fat  diet) competing in the Tour De France on daily stages where breakaways or sprints to break up a pack is the norm and he cannot sprint to keep up then he definitely has no chance for a stage victory.

This is because high fat diets don't just ramp up fat burning, they actually decrease carbohydrate usage by decreasing the activity of a key enzyme called pyruvate dehydrogenase or PDH.

However, if you are doing ultra distance racing then the loss of sprint power isn't a big deal at all since you are more interested in completing the distance under a certain time rather than outsprinting a fellow runner. Especially when a bigger challenge for an ultra runner is refueling. Those of you who have done ultras will know what I mean when you are so sick of eating a sports gel or a banana after 12 hours without needing to go to the toilet.

It will be so much better and easier for your participation if you can rely less on external carbs while drawing on your fat reserves.

Take home message is that the low carb, high fat diet is effective for losing weight (but long term effects are not known).

If you're on the keto diet and exercising and/ or racing at 60% of your V02 max then your exercise efficiency should remain the same once you have gotten use to the diet. This mean that for moderate efforts no problemo, performance is not affected.

However if you're exercising/ racing over 70% V02 max, i.e. when you're going faster, charging uphills, it will not be the best diet plan for you.


Burke LM, Ross ML et al (2016). Low Carbohydrate, High Fat Diet Impairs Exercise Economy And Negates The Performance Benefit From Intensified Training In Elite Race Walkers. J Physiolo. DOI: 10.1113/JP273230

Phinney SD et al (1983). The Human Metabolic Response To Chronic Ketosis Without Caloric Restriction: Preservation Of Submaximal exercise Capability With Reduced Carbohydrate Oxidation. Metabolism. Aug 32(8): 768-776.

Thank you for reading this long article.

*Olympic 50 km race walkers were chosen for Louise Burke's experiment as the event is among the longest in the Olympics, with the winning time just under 4 hours. Also for the rules of sport that forbid race walkers from breaking into an all out sprint, making the loss of high end power less of a problem. Burke published a very famous article called "Fat adaptation for athletic performance: The nail in the coffin?" in 2006.

She, however softened her stance in 2015 with another article "Re-examining high-fat diets for sports performance: Did we call the nail in the coffin too soon?".

Also note that Kenyan runners get 76.5% of their calories from carbohydrates (including 23% from ugali, a sticky and stomach filling cornmeal starch) and 20% from loads of sugar in their tea and porridge.

Ethiopian runners get 64.3% of their calories from carbohydrates (biggest contribution from injera, a sourdour flat bread made from an Ethiopian grain called teff).

If there's a better alternative diet than carbs for better endurance performance, the Kenyans and Ehtopian runners certainly are not following that.

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