I’m on day 3 of a fast now and just tried out running while fasting for the first time (only 4 km / 2 1/2 miles). It felt ok, not so different than usual. I’m not a veteran of fasting, with this a third trial, after doing 3 and 5 days prior. I might continue this to be 6 days in total, or quit a day earlier or later depending on how it feels.
What are concerns or limits others have experienced, related to running or exercise in general while fasting? I would imagine that acclimation comes into play; this time it has all been much easier than the first two. I’ve also been wondering how this is different than running significant distance, since surely glycogen reserves only take you so far on runs. I either run for 4 or 8 km, so 2 1/2 or 5 miles, and I would guess that I’m running on energy reserves towards the end of 5 miles, even when I’m eating. If it’s this comfortable it might be a good way to burn through energy reserves on day 1 to get that transition period over with faster.
I find that adding more sodium or drinking salted water during a fasted run, jog, or ride really helps avoid getting bonked.
Longer fasts and high intensity or endurance cardio aren’t that compatible in my experience, but lower intensity cardio is a very different story. Low intensity cardio like a brisk walk to power walk can greatly facilitate ketosis while fasting.
In any case, the more you train while fasting and the more intensely, the more salt and potassium should be added to your fasting routine