Episode 305 – Does a Ketogenic Diet Help or Hurt Your Endurance?

Written by Jonathan

I’ve been reading the book The Art and Science of Low Carbohydrate Performance by Dr. Stephen Phinney and Dr. Jeff Volek. Which highlights the benefits of eating a low carbohydrate diet and putting your body into ketosis as a healthy way to live and a good way to do endurance exercise because our body is capable of storing much more fat than carbohydrate therefore we should be able to theoretically exercise for longer periods of time. What I like about this book is that it is in direct contrast to some of the other books I’ve just read. The End Diabetes by Dr. Joel Fuhrman being the most prominent where he states the exact opposite saying, fat especially saturated from animals should be avoided and you should eat mostly carbohydrates from plant based whole foods, on top of this he states the ketogenic diet is a dangerous diet and it should be avoided. These differing viewpoints come from Medical Doctors and researchers and it’s interesting for me to see how such educated people can come to such different conclusions. I really like having these differing opinions because now I can read into both and make better decisions for myself.

Now I apologize in advance because this isn’t a must read episode for The Art and Science of Low Carbohydrate Performance, it’s more of a review of a research article the book cited. That’s right there was a citation that I thought was questionable so I tracked down the original study and decided to critically analyze it to see if what the authors were saying was true and if this was a legitimate study that I could take seriously. The line in the book that got me questioning the citation was this, that when elite cyclist were not ketogenic adapted they were able to pedal a bike at over 900 kcal an hour for 147 minutes and when they were ketogenic adapted they were able to ride on average for 151 minutes and that this was not statistically significant, to which I said neh, neh that is a 4 minute difference which I know doesn’t sound like a lot but if these elite cyclists were in a race that would mean if the keto group were in first then the rest would be somewhere between 1.5 and 2km behind them which in the elite cycling world is a huge difference, so different the T.V crews wouldn’t even be following the non keto adapted group, so I wanted to dive in and see what this study was all about.

The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation with the lead researcher being one Dr. Stephen Phinney the same person who wrote the very book I was reading. I will angalsize the title and explain the experiment to you, because it’s much more interesting than the title suggests. I do have a link to the research article in the show notes if this interests you and if you want to come on the show and discuss it with me after you hear me on here I would love that, just send an email to info@fitnessforfreedom.com back to the study. They took a bunch of elite or well trained cyclists that were not keto adapted, meaning they were eating carbohydrates and burning lots of carbohydrates while exercise and they had them cycle between 60 and 65% of their maximum capacity for as long as they could, as long as the participants stayed above 60 rpm, while doing this the researchers measured the cyclists oxygen and carbon dioxide consumption and output, they took blood and muscle biopsies so they could do all kinds of tests, then after this initial test the put them on a keto adaptive diet, where they were eating less than 20g of carbohydrates a day then the remaining part of their diet was two thirds, fat and 1 third protein and the cyclists supplemented with vitamins and minerals to ensure they were getting everything they needed there, then after 4 weeks of this diet and maintaining their regular training protocol they redid the cycling test at 60 to 65% of their maximum output and all the same measurements were taken and these were the topline stats I had read in the book, the non-keto group was able to ride for 147 minutes before they could no longer keep up the required rpm and the keto group could do 151, done deal.

But let’s take a closer look at this study, maybe give it a bit of a critical analysis. To start it was done in 1983, which truthfully may be fine, but there’s a good chance there are multiple similar studies that are much more recent and with a larger test group, because this study only had 5 participants which means it’s not enough to draw major conclusions on, but on the bright side the researchers posted each individual’s results which is where things get the most interesting out of the 5 participants, 1 of them performed substantially better on the keto diet, for lack of a better comparison he might as well of done a cycle of steroids and taken EPO because his time, when he was not keto adapted was 148 minutes, but when he was keto adapted he could go for 232 minutes, that’s over 50% longer. Then on the other end of the spectrum one of the participants went from 169 minutes to only being able to do only 121 minutes that about 30% less time, then there was a participant who did marginally worse and another who did marginally better and then one who was almost identical for time.

So my conclusions are this when you average them all together, sure you could argue there is no difference, but once we look at the individual participants we can realize it really had no effect on only one person and for two it made them much better and for the two others it made them worse, so what does this mean for you? It means if you’re interested in a keto style diet or you feel like you should be able to perform better than you currently are for endurance sports you should try it out and see how your body responds, but to do it properly there are a couple things you need to consider.

1. It takes 14 days before you become truly keto adaptive and you’ll probably go through a period of not feeling very good where you’ll have to push through.

2. You should probably do this under the supervision of a dietetic professional that is well versed in this type of change.

3. Do a pre and post test and similar conditions, this means use the same parameters on a treadmill or stationary bike where external forces can’t get in your way and wreak havoc on your results

4. You should probably talk to your doctor about it to see what they say and if you have access to measuring your blood work numbers (cholesterol, fatty acids, blood sugar etc.) that could be really interesting for you as well.

And brings me to the last part of today, this study also highlights some really interesting findings with respect to energy source ratios, blood glucose, cholesterol, fatty acid levels as well as glycogen stores and that’s what we’re going to talk about next week. If you would like to hear that show hit the subscribe button so you don’t miss it.



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