I'm an adult male endurance runner, and earlier this year took on a moderately low-carb diet and became fat-adapted. My runs at first were your predictable sufferfest but after 6-8 weeks I got to a point where I ran a 50k ultra without taking in any calories. In previous 50k races I needed to eat carbohydrates to continue.
Then, after a couple of months of this, summer and vacations and stuff happened, and I discontinued the diet. Now it's October, and I'm resuming the low-carb - but my runs are, once again, suffer-fests. Which got me to thinking:
How long did the fat adaptation last after stopping the diet?
Since the fat-adaptation is apparently lost, should I expect it to take another 6-8 weeks to regain it, or will the process be faster the second time?