I think I heard it on the FoundMyFitness podcast which has excellent discussions about fasting science. I think it may have been the last interview with Valter Longo. I’ll see if I can dig it up, but their website would be a good starting point.

"Someone said so in an interview" isn't really compelling evidence. Do you know of actual evidence of this? Studies?

No idea why you're being downvoted. Even when videos/podcasts cite studies, it's difficult to verify that the study actually supports their claim since it's often difficult to find the study they mention.

The 18 hour claim may be supported by evidence, but there isn't any in this subthread so far.

Feel free to pore over thousands of scientific papers about the benefits of fasting on NCBI for us and let us know. Until then, I'll take NutritionFacts.org videos' word for it: https://www.youtube.com/channel/UCddn8dUxYdgJz3Qr5mjADtA which cites scientific papers as it makes claims.