It was interesting to come across this thread right now. I restarted running about 5 months ago and for most of the time I was low-carbing, but not in ketosis. I decided to try to get stricter to lose more and have been in ketosis for about 4 weeks. Immediately I found running harder. My pace slowed way down and all my runs are hard (I don't go really long, generally 30-35 minutes running time, 3-4 times a week). Then I had a cheat day yesterday, and today's run was fantastic! My pace was 10% faster, I felt great, I felt strong and energetic.

I'm glad to see my experience that the running is slower and harder while doing a stricter low-carb is normal and that in the end, it doesn't really matter as far as weight loss and fitness. If I get to the point that I decide to do more 5k or 10k runs, I'll consider carbing up before a race, but for now, I just want to lose more weight!

Val