If you could run at a pace that doesn't require much in the way of glycogen, then it shouldn't really matter. There was a cyclist who posted on here that a metabolic test of some sort revealed that at 65% of VO2Max he was burning all fat and that at 80% it was 50/50. It would take considerable amount of training to reach that point, but if you're able to run a marathon, you'd likely be there.

I'd check out crossfit endurance for some training ideas. Those guys have a great thing goin on and run marathons /ultamarathons on a paleo diet with improved performance

I should add that a general paleo approach (100 ish grams of carbs) is good to adapt your body wothout worrying about 'very low carb'

I enjoy doing 12 and 24 hour mountain bike races 2-3 times a year. it's been my experience that I can train my body to burn fat more efficiently by staying below a certain threshhold during long rides, do lots of HIT training and cross training, and stick to a fairly strict paleo diet. I turn to fruit and fat when I'm feeling hungry after hard workouts, never high carb processed foods. Sometimes I hit up the Souper Salad buffet if I have a hunger that is huge. I do not carb load before any of my races. Come race day, I'll go a few hours before starting to get hungry. I'm drinking a lot and nibbling on some larabars during the first few hours. as soon as I feel the slightest hunger, I starting downing fruit like crazy. pineapple, grapes, strawberries, mango ,etc. I continue to eat lara bars and drink a lot. When it's getting close to the end and I can just sense that my body is really breaking down, I break out muffins, goos, pizza, and whatever else looks good and I think I can hold down. If this is a 24 hour race, this probably occurs at like hour 18 or so. I haven't always done these races while on the Paleo Diet. In fact, my first one, I had never even heard of the paleo diet. I was craving bread, sugars, and all sorts of processed crap only 3-4 hours into the race. I still did well at that race, but my energy was full of ups and downs. These days, I can go harder for longer, and at a more consistent pace. i strongly believe it is because I can burn fat more efficiently, but it also has a lot to do with the way i train (staying under threshhold and doing HIT) even if I starting going for the muffins at hour 12, that is a 300% improvement over 3-4 hours when I was pre-paleo. So to come back to your question, you can rely on fat for energy in endurance events, you just have to build up to it and not exceed your threshhold. hope this helps.

No way......an article just got published about cardiac myofibrosis and early death in endurance athletes. I will get the link here. The controls had zero fibrosis. Endurance kills! Journal of applied physiology feb 17 2011. M. Wilson et al. Diverse patterns of myocardial fibrosis in life long veteran endurance athletes.

http://www.ncbi.nlm.nih.gov/pubmed/21330616 Edit for direct link.

This strengthens my point on endurance. Avoid it. Do HIIT!

Anthony Colpo just posted two articles about LC for athletes:

http://anthonycolpo.com/?p=1498

http://anthonycolpo.com/?p=1535

Also, last summer I talked to Steve Maxwell (who has probably done every diet on the planet ;)) at his seminar and he said while low carb works you will probably not perform as well as you would with higher carbs.

Personally I don't do any long endurance stuff but I haven't noticed a decrease in performance with HIIT and strength stuff.

Thank you all very much for sharing your experiences and thoughts on this "Idea" of mine.

Special thanks to Bobby D and Caveman Greg.

Taking some of the snippets of information that you've all left here and running with it + Doing a lot of reading. I've sort of concluded the following:

Although both Fat and Carb metabolisms both produce ATP, the lipid metabolism (fat) takes longer to produce the same amount of ATP as the glycolysis metabolism (carb). This means that the greater the body’s energy expenditure, the less able the lipid metabolism is able to keep up, forcing it to rely more and more on glycolysis.

However, the glycolysis metabolism only has a storage capacity of between 1,200Kcl to 1,800Kcl meaning that it can't last for the full length of the marathon. Even if supplementing carbs whilst running (maximum intake of 200-600Kcl per hour while running - depending on carb type)

The lipid metabolism has a storage capacity of over 110,700Kcl (based on my individual stats of 82Kg and 15% Body fat) which certainly can last a marathon.

From the research I have done, the main reason why most endurance athletes opt for a high carb approach is because they are operating above their aerobic threshold (65%-75% MHR – depending on where you read about it) at which point glycolsys plays a more significant role in ATP production. As soon as the glycogen runs out they "hit the wall" as it’s often referred to.

I believe that by staying below the Aerobic threshold for the duration of the marathon could allow a person to complete a marathon on a Low Carb diet.

Training therefore will focus on firstly increasing the Aerobic threshold to as high a point as possible. Hopefully this will allow me to go as fast as possible whilst using the lipid metabolism without depilating my Glycogen stores. My first guess would be to use techniques like Sprint intervals and the Tabata Protocol (Although Tabata's main emphasis is for VO2 max increase. All thresholds should increase with it including the aerobic I'm interested in - if I'm correct)

Secondly, I'll be looking at developing a more energy efficient running style. Greater efficiency = less energy usage = more likely to keep my heart rate below the aerobic threshold. "Pose" caught my eye but I'll look at others before starting a training programme.

Finally, I will include longer runs to gauge if all of this theory actually works. I’m not really sure how far one can increase the Aerobic Threshold but I’ll do more reading on it.

Feel free to pick holes in my logic here everyone. I’m not suggesting that “I know it all” even for a second, but I am keen on trying this out.

Nick Kinsella

Gilliebean ran a marathon while eating Paleo, it can be done! I bought into the whole carb loading thing my first two 1/2 marathons and gained weight!

You can definitely do it, but it's best to train the entire time eating Paleo. You don't want to switch last minute and confuse your body.

Very interesting question, Nick, one I've debated in my own head many, many times. I'll share with you a little of my n=1 experience.

I've done marathons "pre-paleo" and marathons since becoming paleo. Since adopting a paleo style of eating, I've competed while eating paleo low-carb, and I've competed eating paleo moderate carb. I found that eating paleo moderate carb is the best way for me. Keep in mind that, whatever you choose, you'll want to stick with a consistent eating style all through training and the race. Switching things up right before or too often will be counterproductive.

I ran Boston 2 years ago. My training involved a weekly long run of around 17 miles, a 5 mile tempo run mid-week, and an easy 7-10 mile run at the end of the week. On the days in-between, I did tabata sprints (warmup+tabata+cooldown totaled about 20 minutes). My weekly mileage was not very high (~ 40 miles) but doing a weekly long run and all the high-intensity work served me well. My diet was 80% paleo, and I didn't go out of my way to carbo-load, but I did eat potatoes and bread. I even fasted for most of my long-run days and didn't suffer any bad effects.

I ran 2:36 that year (we had a headwind that year, not a tailwind like this past Boston!) and had consistent energy throughout the entire race. That was a great experience.

Last year I stuck with a paleo low-carb diet while training for a spring marathon. My weekly mileage was a little higher (~ 60/week). While remaining low-carb, however, my energy for training was inconistent, my long-runs suffered, and my mental energy was really bad. I ran 2:45 for that marathon, by far my slowest marathon.

My diet now actually more resembles WAP than paleo, as I include lots of raw dairy, lots of potatoes, and homemade sourdough bread into my diet. For running, the most important thing I do is one day a week, I run in the morning on an empty stomach. I like to do this for my long runs to help adapt my body to better burn fat at faster paces, so this usually happens early Sunday morning. Once you are fat adapted, you shouldn't need to concern yourself with carb-loading.

I make sure to eat lots of fat and protein, and plenty of sea salt for my adrenals. For eating carbs, I'm usually between 75 and 100 grams a day, adding 10 grams for each mile I put in that particular day. I do think carbohydrate is important for recovery (and also important for the krebs cycle), although some may disagree. If you plan to train a lot for this marathon, a paleo style of eating will serve you well, but don't restrict your carbs too much.

How do you plan to train for this marathon? A 30-minute run is drastically different from completing a marathon, so even if you don't notice a drop in performance there, it doesn't really tell you anything about how you'll feel 20 miles into a marathon.

I've ridden 100 - 300km one-day cycling events since going low-carb paleo and have had good success. I do nothing out of the ordinary leading up to the events, but take higher carb fuel sources on the bike. I'll have a couple of sugary drinks, a few "energy bars" my wife makes me (dates, coconut oil, coconut, macadamia, chocolate), and have sometimes eaten the insides out of sandwiches provided at feeding stations. This season I'm planning on experimenting with some kind of starch/fat source concoction (uhh...buttery yam gels?)

Have you checked out Mark Pomery, the paleo triathlete?

http://swimcyclerunonline.com/

When I ran marathons, I relied on heavy carbs but that was pre-paleo.

I assume you are doing long runs most weeks to build your mileage. There are 3 reasons for the long runs - build physical endurance, build mental endurance, and practice eating/drinking.

My routine was a high carb dinner the night before, fruit and oatmeal 30 minutes before the race, handful of raisins at miles 6, 10, 15, and 22. If I were doing this now, I'd probably eat a high fat dinner and then eat 3 or 4 eggs before the race, keep eating the raisins and drink coconut milk with some MCT oil added to it instead of water - but only after trying it for the long runs to dial in the amounts.

By the way, I no longer run marathons because on an easy training run (only 12 miles), my heart went into afib and I had a mild stroke and consider myself lucky to be alive and relatively healthy - other than the permanent damage I did to my heart.

Noooooooo!!! Unless you want your performance to suffer, then sure!

I'd say you really don't have to worry about it until before the race and just make sure your glycogen stores are topped off. Generally, if you're low-carb paleo, you're going to be a fat burner anyway, but something like a marathon will probably require glycogen for a good portion of the time. I've done long days of exercise (6+ hours hiking, snowboarding, etc), and while not as intense as a marathon, they do require good fueling. Generally the night before I'd have a full sweet potato and the morning of a big glass of grape juice (good glucose:fructose ratio - glucose preferentially fills muscle glycogen and fructose preferentially fills liver glycogen) and I was good to go all day without refueling. Maybe a similar strategy can help you on a marathon. You can always do a few practice runs and see what works best for you.

Hank at My Low Carb Journey just completed his first half-marathon while VLC and seemed to have done well. His time was certainly faster than mine! :p http://mylowcarbjourney.com/2011/05/thoughts-about-my-first-half-marathon/

A more ketogenic diet (high fat, very low carb) will help you maintain a more regular supply of energy. I run semi-barefoot 5 to 10 miles at a time and much prefere zero carb running to high carb.

You'll find keto and paleo relatively similar with keto but next to no fruit if any. You'll no longer 'hit the wall' and you'll just have to concentrate on your physical training.

FYI... Zero Carb salt / Electrolytes replacement drink

NO, but a high carb version is.

paleoista.com

http://waroninsulin.com/nutrition/the-interplay-of-exercise-and-ketosis-part-ii