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The body stores about 1800 calories of glycogen, give or take. When marathoners hit "the wall" after 15-20 or so miles they have mostly depleted these stores and are having trouble adjusting to burning fat.

If I train in nutritional ketosis, theoretically my body will be used to using fat as a fuel already, right? So then shouldn't I be able to run a marathon without hitting the wall?

I've run 3 marathons in the past eating lots of carbs during training and I'm gearing up for another. Have any experience marathoners played with this?

I know that marathons can be run on a paleo diet just from other PH threads. What I'm asking here is, could it actually advantageous to train in ketosis?

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Thanks for asking the question. I do "big" hikes, 20-30 miles, strenuos terrain I have defintely hit walls in the past. – treeees May 2 2012 at 20:46
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 The logic seems good, though there may be downsides. You can probably run a marathon anyway by running on a fat metabolism heart rate - to run faster would require a glycogen metabolism. What I'm trying to get at is that you may avoid hitting the wall, and you may increase the range of effort/HR at which you can run on fat metabolism, but you may still be slower than a conventionally run marathon. One additional question would be how do ultra runners deal with this - running 6 miles after hitting te wall is tough, running 50+ surely requires another strategy. – sam_acw May 2 2012 at 21:25
^ there's your answer. Spot on sam. – Scotty Von Porkchop May 3 2012 at 10:40
On ultras they eat full-on meals as they run. – PrimalDanny May 3 2012 at 12:45
And running faster doesn't do you much good if you grind to a halt before the end. Besides, if you train in ketosis but fill up your glycogen before the event then you can tap all the sprint power you, er, want and still keep ticking. – PrimalDanny May 3 2012 at 12:50
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Read Volek's new book on exercise performance. He offers the case studies of quite a few ultra-marathoners - folks who do 50, 100 mile runs - who live in ketosis just for the advantage of always have steady fuel during these very long endurance events.

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 Is that The Art and Science of Low Carbohydrate Performance? Looks awesome. Can't wait for it on Kindle – Sam May 3 2012 at 12:38
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 Yup. Peter Attia the marathon swimmer also does this. He's posted his ketone & performance values. – GurlzLuvSteak May 3 2012 at 14:27
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Steve Phinney has shown that keto-adapted athletes utilize muscle glycogen at a lower rate during sub-maximal exercise. Of course, when you are in ketosis your muscle and liver-glycogen stores are much reduced over someone that has carbo-loaded.

It's like having two leaky buckets, a full to the brim carb-loaded bucket with a big hole, and a half-full keto-adapted bucket with a much smaller hole. Even though one is much fuller than the other, they'll both empty out in the same time: http://www.nutritionandmetabolism.com/content/1/1/2

Of course, once your glycogen is exhausted, the keto-adapted athlete is in a better suited to running on stored fat. The alternative title for Phinney and Volek's new book is "the art of avoiding the bonk".

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I'm not an "experienced marathoner", but I implemented the Volek/Phinney program and ran a trail marathon in ketosis. I wrote up a report on mark's daily apple:

http://www.marksdailyapple.com/forum/thread64390.html

I'm not convinced that there's a performance advantage, but I don't have an apples to apples comparison. Recovery seems to be improved though, which could be very important.

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Thanks for the details. I just linked to your report on ketotic.org/2012/12/bcaas-and-keto-diets.html – Ambimorph Dec 31 at 18:53
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I don't do marathons (longest I ever did was a half). I used to do 10k races a bunch, but since switching to Crossfit and paleo full time, I haven't done any long-distance trainings. I still do one 10k a year for fun, and I've been drafted into some 24-hour relay events where the legs are on the order of 10k or so. So take this for what it's worth coming from an anti-endurance mindset and training style.

I have had my best ever 10k races, both in best times, and felt the best during and afterwards, when I've been keto adapted. In fact my last 10k that I did, I ran it in a fasted state. I woke up, drove to the start, ran. I had an awesome feeling of constant energy, never really got tired. I couldn't ever pick up the pace to sprint past anyone but I had a great constant energy. I never felt anything like it. I totally think that it would extend to a marathon if you wanted to try.

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Honestly, I'd be surprised if training in ketosis does you any good. "Hitting the wall" is not this inevitable occasion, it's just what happens to a lot of people that do marathons.

A better focus, in my opinion, is to build up your muscular strength and endurance. As your muscles get built up, you will be able to go faster and farther using less energy. I just don't think there's as much to this "keto-adapted" thing as people give credit for. Sure, your body will probably become more efficient at it as you do it more, but to the extent that you'd be better off training in ketosis for a marathon is the wrong approach.

If nothing else, the biological mechanism of ketosis and running marathons are completely antagonistic to each other.

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 That seems to be a flat contradiction of any credible work I've read or what I've experienced. Is this just good ol' fashioned scepticism or do you have something against ketosis? – PrimalDanny May 3 2012 at 12:48
I guess I didn't explain it to your liking. Ketosis is very much involved, but training in ketosis is probably less effective than simply training with the intention of improving performance. The idea that there's this awesome way to train for an endurance event that no one has figured out is pretty ridiculous. Running out of glycogen is not a typical thing and it doesn't happen to people that are in good shape and train properly. – Dylan May 4 2012 at 3:17
Simply put, the focus is off. It's not about "ketosis". The intensity at which you perform will determine what portion of fat stores and glycogen you are burning up. If you are in straight ketosis, it will limit your ability to perform and therefore limit your performance gains. I'm not talking about just sprinting the whole way, I'm just saying that a lot of people have run marathons and there have been a lot of different approaches, this is one subject where people have actually figured it out. – Dylan May 4 2012 at 3:21
Yup it's possible to train as an elite marathoner and be able to stretch things out for a few more miles, which is all they need. That seems to almost entirely miss the point. Just how much muscular strength do you think you need? Some people may have some things figured out, but I don't think you're one of them. – PrimalDanny May 11 2012 at 23:28
I'm not talking about getting buff so you can compete in an endurance competition. I can't really see why you would think what I'm saying is incorrect other than if you're misinterpreting it. If someone runs 50 miles, a huge proportion of their energy will come from fat. But when people use the term ketosis, they aren't talking about burning fat, they're talking about burning ONLY fat. A person who runs 50 miles burns mostly fat because their muscles are fit and running requires a lesser amount of exertion than it does for most people. – Dylan May 12 2012 at 14:09
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Take a look at http://www.marksdailyapple.com/how-to-fuel-a-marathon/

Mark talks a bit about "Train Low, Race High"

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