I can speak to this a bit. I practiced intermittent fasting (eating once per day) for nearly a decade, while maintaining a very low activity level. My resting m

I can speak to this a bit. I practiced intermittent fasting (eating once per day) for nearly a decade, while maintaining a very low activity level. My resting metabolic rate dropped significantly during this time (down to about 1300 kcal/day). About a year ago, I increased my activity level significantly (distance running, hiking, strength training, cycling) and quickly found that: a) I wasn't recovering quickly enough b) It was extremely difficult to take in enough calories for a day in a single meal c) I had very low energy when in ketosis Eventually I gave up and just started eating on a typical 3-4 meal a day schedule. My RMR steadily increased back to baseline, I got a lot more explosive energy, my body began responding much more rapidly to training, and my recovery speed improved significantly. Personally I think that intermittent fasting is not a good idea if you are very physically active. That's just my opinion from my own experience.