I recall an interview with Valter Longo in which he said the fasting-mimicking diet was just because patients were more comfortable with eating a special diet t

I recall an interview with Valter Longo in which he said the fasting-mimicking diet was just because patients were more comfortable with eating a special diet than with a full water fast, and doctors were also more willing to recommend the FMD than a water fast, because it seems so extreme to people. So you certainly can just do a water fast instead.