I am doing 18:6 fasting (eating window 12-6pm) and run in the mornings fasting. I much prefer running fasting! When I do a run between lunch and dinner I feel heavy like my body is trying to digest and exert at the same time. Running in the mornings is great!
Edit: my runs are 3-5 miles typically
I have been doing IF (16:8) for 2 1/2 years and started running seriously 2 years ago. I have had no issues running fasted and actually prefer it (as others have said). I just make sure to drink lots of water before and during my runs (if over an hour). I also drink black coffee in the morning so I think that helps with the energy for the run.
I trained for and ran a half marathon, all while doing IF and had no issues. As my longer runs increased to over 10 miles, I did start taking a gel with me and breaking my fast with that about half way through my run, as I knew I would be using gels for my race and didn’t want to try anything for the first time on race day. Sometimes that meant breaking my fast at 9:30am instead of 11am, but I really didn’t worry about it.
I’ve been running since 2007. Did the Chicago marathon that year. Have done half marathons just about every year since (minus 2020 because of COVID cancellations). I did IF for almost 3 years (1,000 days, to be exact). I found that running while fasted, regardless of distance, was totally fine for me. It is important to be well hydrated though, so drink lots of water. As an aside, I hate coffee so drinking water only was easy for me. I know lots of IF folks like coffee, but I don’t.
I don’t expect that one day a week would mess everything up, I think you would be totally fine with that. But you might want to post this same question in r/running, it’s a super active sub and I’m sure there are other people there who do intermittent fasting and have experience incorporating long runs or marathon training into their lives with their eating schedules.
🙋🏻♀️
During Covid when I was WFH, I did 3 miles in the morning. I didn’t have to worry about showering and getting ready in a hurry lol It’s too much for the morning now that I’m back in the office, so I go after dinner. My dinner is light though, lunch/snack are my big meals
I’m curious why your doctor recommended running inside your eating window; was that due to personal health circumstances? There’s a good amount of information out there on training while fasting; here’s a video on fasted resistance training, and here’s one on fasted cardio. (Don’t be put off by the “bro-science” thumbnails; these guys know their stuff, and they’re citing studies as they go.)
In short, it looks like there’s no harm in training fasted, and there may be some benefits when it comes to muscle growth and fat loss.
This is all inspiring! The dr didn’t say to workout between meals for any specific reason with my health, it just sounded like his general advice for people on an IF schedule. So far, doing just two miles while fasting has felt fine. So as long as I’m feeling ok I’ll just keep going!
Good note on adding in the gels for longer runs. When I’ve done half marathons in the past I’ve used those gels. I usually would have oatmeal before my long runs, too. But I’ll see how I do with out this time around.
I started running again(ish) in August 2022 and started IF in October ish. I do not eat breakfast on weekdays, and eat lunch only some days.
I’m on a short break from running last couple weeks due to a throat cold and generally miserable weather, but I’ll be back at it soon. I prefer running early in the morning, between 5km and 7km, and I always run fasted and stay fasted several hours after.
I will say this though: if I push speed and HR up, running on glucose I guess, I’m going to wind up pretty sacked for hours. If I can run in fat burning HR range (zone 2 I think?), all is good. Happy as a clam running on empty.
YMMV