Three weeks ago I did an 8 day water fast. Not my first, I have done multi-week fasts in the past. In my experience, unless your baseline starting weight was above normal bmi, you will put the weight back on.
I play tennis and for the last 8 months I have also been distance running regularly. I have found that fasting substantially damages my performance necessitating a refeed back to baseline in order to recover my strength, power and general fitness. This is evidence that fasting from a normal weight is negatively catabolic.
This may not be a popular view but I have come to a personal conclusion that if you want a lower weight---while also maintaining or, ideally, increasing your power to weight ratio---you need to earn it through high volume exercise and activity.
For lean fitness to be sustainable long-term, you need to commit to a sport that demands fitness/athleticism. Different sports, different body-types
The experiences of others may differ, I would be interested to hear these.