Definitely not a fad per se. They way it is packaged (Keto) and delivered to the masses makes it seem fad-ish as all quickly ramped-up-to-make-money deals tend to be. I've used keto myself several times though only as short-term diet change. I myself never fully seemed to recover from the Keto-flu even after months of eating strict keto. Adding back natural complex carbs helped me immensely in that regard.