I would argue it's definitely not a fad (at least in the sense it's something that's been happening only very recently); people have been fasting for literally

I would argue it's definitely not a fad (at least in the sense it's something that's been happening only very recently); people have been fasting for literally thousands of years, though mostly for religious reasons. It has an aura of being a fad nowadays since some modern research has indicated it actually does have health benefits, which I think some people have been a bit too quick to pounce on.