Two possible factors for harmful effects of endurance sports are: 1. carbo loading for glycolysis 2. repetitive stress(chronic).
If we isolate these two factors and if we ask whether athletes in marathon/triathlon can perform just with krebs cycle(body fat is sufficient for ironman calorie expenditure:8000 - 10000 calories ). For simplicity of argument, let us worry factor 2 separately. Then problem is reaction rate for krebs cycle is FAST enough to provide required energy expenditure during ironman triathlon? If sufficient, then we can worry factor two. If insufficient, then athletes may experience a number of debilitating difficulties with DNF(do not finish) result. Among nine reaction paths in citric acid cycle, which one is slowest? Or Acetyl-CoA from beta oxidation requires NAD+ in isocitrate , a-ketoglutarate ,and malate dehydrogenase steps of krebs cycle. And can NAD+ be SCARCE to slow down reaction rates?
If we understand principal factors for reaction rates during endurance, what are possible corrections can we make to resolve this problem? Personally I am a paleo practioner and do not found any problem in krebs cycle reaction rates during sprint and other performance(gym rings). But before I experiment my body for continuous endurance requirements, I would like to have theoretical understanding of risks involved.
This is triggered by interesting question by dexter "... endurance athletic competition -- like marathons and triathlons are ok? ...".
Well, this may not answer your question directly, but it gives you one more data point. Before I started doing Crossfit 100% 3 years ago, I used to run relationally. Now I do no training thats longer than 20 minutes and it's all high intensity stuff. But once a year, my city has a big 10K, so I do that just for fun - no training, no warm-up, just wake up and go to the start line. This year I decided to do it fasted and keto. Usually I do it with some extra (paleo) carbs. I did the 10K in 50 minutes, which is my usual post-Crossfit time (I used to be a 55 minute runner when I actually trained for it), but it was a weird feeling in keto. I felt like I could have gone all day at that pace. I wasn't tired at all at the end, just felt great. But, I couldn't have gone any faster. I tried a few places just to pick up the pace and I just couldn't. It was like I had this endless supply of energy, but the power was locked and I couldn't get any more.
So to your question: I bet you could to a marathon or triathlon keto and go at a good pace all day (I swear I could have), but you probably won't have the any bursts of speed available to you (even the last 100M I couldn't pick up the pace).
Athletes can require 10,000 calories per day. Even intense weekend warriors can need 7000 calories. I have a friend that falls in this category. If you are pushing into your anerobic heart rate you are burning more glucose than fat.
You need to replenish the calories in some way. Most folks I know use carbs of any type. However it would be nice to hear from someone if coconut works for them as well.
Are there any PaleoHackers that still think endurance athletic competition--like marathons and triathalons are ok?--Art DeVany reports a physician death by triathalon and a debilitation by triathalon. Would you as a paleohacker consider entering 13 Answers