Running just before the end of a 24 Hour fast

(David Cooke) #1

I had a bulletproof coffee and set off on a 2 1/2 mile run after fasting 24 hours. Anybody else tried that? I was very slow although I felt I was putting the usual effort in, and came back feeling exhausted.and a little dizzy.
I wasn’t going to run but I felt really good about the idea.
I don’t think I’ll be doing it again!
I am usually fasted 18 hours when I go run, 24 seems a little too much.,


If you felt a little dizzy were your electrolytes topped up? The feeling of exhaustion is what I had earlier in the year when I wasn’t actually fat adapted. But yes a couple of times I’ve done a 7 mile run after being fasted for 36+ hours and making my fast about 40 hours in total.


Yes, I started doing this regularly at some point. Big mistake I soon realized so i stopped. No matter how fat adapted one is, a 24 hrs fast is too long and it is notmal to feel dizziness and weakness. Plus my performance was very low during these work outs and i figured out there is no point to train like this :slight_smile:

(A fool and his bacon are soon parted) #4

Electrolytes are more likely the problem. You were also probably a bit dehydrated, which resulted in hypovolaemia—in other words, your blood volume was a bit down, which forced your heart to have to work harder to keep your tissues oxygenated. You wouldn’t have noticed, if you hadn’t decided to increase your O2 requirement by running.

A cup of bone broth, taken about half an hour before your run, would have prevented the problem. Try it, the next time you feel like going for a run while fasting.


This is simply not true.
As I said above I have run up to 7 miles after 36+ hours of fasting. As I said probably electrolytes or as Paul added, dehydration.



(David Cooke) #7

So let’s assume that although I did hydrate and electrocute myself that day same as every day, that fasting depletes your sodium reserves. Thanks guys. As I said, I don’t plan to do this again, I may even eat on the evening before my next race.


I exercise fasted all the time and feel great. I think exercising with a bellyful of BP coffee wouldn’t be much fun though :nauseated_face:


Nope. I’ve done weights as well as Bikram classss on the 3rd and 4th days of a fast and felt amazing, and I’m not alone. You shouldn’t do it if it doesn’t work for you, but the statement above is simply not true.


Maybe the daily electrocution is the real issue here?

(David Cooke) #11

I didn’t feel like using the word electrolyte as a verb.


Fasting would definitely deplete your electrolytes. If I remember (which doesn’t seem to be very often :-/ ) I would have some salt water before going out. I have just done a half marathon race with nothing different food wise apart from just an avocado for breakfast. No carb ups and no fluid/food whilst running. Maybe you would adapt to it more if you did it more?

(Central Florida Bob ) #13

I think the 18 vs 24 hours and all might have to do with your percentage of fat available. I know there’s a lot of reference to a paper Richard found showing we get 31.5 calories per pound of fat per day, but I’m leery of “one size fits all” numbers like that. I’d expect some sort of range, and I’d expect experienced runners would get more energy out of fat than someone just starting out.

Since last May, I’ve been cycling for an hour at about hour 39 of a 42 hour fast, three days a week. It’s hard to compare times on a bike, even over the same course, because the effects of wind are so big, but I didn’t even record times. I just went by how I felt and I was feeling pretty normal. Of course I wasn’t as fast and strong as I want to be, but I never have been.

In the last week or so, I thought to experiment by bringing the ride up to hour 15 - a full day earlier - to see if there are any changes. Due to a run of crappy weather, I’ve had one such ride, Tuesday (day before yesterday). What I noticed was that on my fasting days for the last few weeks, I’ve been getting cold. Cold hands, cold feet. On that one day, I didn’t get that. I’m anxious to see how that works out tonight.


Hmm…interesting. Maybe i just love food too much :smiley: to me running and HIIT after 24 hrs fast was very not productive and I felt soo hungry after 24 hrs. I do not have almost any body fat to keep me running without food for so long :slight_smile: i don’t know.


Yes, it’s not for everyone. I’ve learned to take salt before my workouts and I think I noticed a big difference when I started doing that.
In any case, less body fat definitely means you have fewer reserves, and you should go by what feels right for your body!

(David Cooke) #16

More to this than I thought. I will in fact try again, but next time will take double salt immediately before running. I went running this morning, only a bulletproof coffee since yesterday and I had a row of personal bests including my first 2 kilometres + in 12 minutes. (previous best 1.79 Km).