Running fasted
What effect does fasting have on endurance performance? All the conventional wisdom says that you need to eat at least once an hour during endurance training otherwise you’ll run out of energy and “bonk”.
This is certainly true for athletes who are unaccustomed to fasting. Their bodies are conditioned to use carbs for energy during exercise but the body can only store about 1,000 calories of carbs at any time. 1,000 calories is about an hour of running, so once depleted, these stores need to be replenished in order for the athlete to continue.
I used to follow this advice to the letter on my long runs. I would eat an energy gel every 45-60 minutes and hydrate with Gatorade, and if I didn’t do this then there was a good chance I’d fail to complete the distance.
This felt wrong to me.
So I’ve been trialing intermittent fasting and its effect on long distance running and have found that, in my case, I no longer needs the gels or the Gatorade. For instance, last weekend I ran for 2:30 on an empty stomach and consumed only water during the run - and I still felt strong at the end.
Fasting has conditioned my body to use fat for energy so it saves the glycogen until it needs it (like sprinting for the finish).
I’m not the only one to notice this. Peter
Attia documents the effect of a
low-carb diet on athletic performance, and concluded that conditioning
the body to run on fat, rather than carbs, will significantly improve
endurance performance.
What are your thoughts on fasting and endurance sports?
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