It’s always best to get one’s nutrients from a healthy, well-balanced diet.
Get supplements as needed as, you guessed it, a supplement to that. :-)
As for fasting, we do 12 hour fasts. Have an early dinner and then, usually, nothing til breakfast the next morning.
Works for us.
The only supplement I take on a long term basis is NMN and only because it isn’t available naturally in large enough quantities, although I do get plenty of B3 through wild salmon, kale, walnuts, etc. Fasting can have both positive and negative effects on the immune system, depending on the duration and type of fasting. IF now is 19-20 hrs but it does temporarily suppress the immune system (until re-eating) so during Covid it was more like 14-16 and I’m not doing 24 anymore. Hope there is a mimicking pill for this soon. :)