I don’t think it’s sustainable either. I don’t dispute that people have lost weight, and if they feel great then more power to them. But personally, I felt like crap without (healthy) carbs. I felt like crap eating vegetarian. There appears to be valid scientific arguments on both sides of every diet debate, so I have decided that I am going to stick with cooking from scratch, and eat what I want in moderation. But I’ve always done IF without realizing it was a thing. I rarely eat breakfast, basically a snack in the afternoon, and I eat most of my calories at dinner.