As a person of normal weight, I tried a keto diet a couple of times but just couldn't get it working under vegetarian/vegan dietary restrictions for a daily work + workout schedule. I got either underfed to the point of fainting, had to rely on expensive restaurant meals and questionable supplements, or had to spent an enormous amount of time on meal preparation. So either I approached this in a completely wrong way…
Scientific evidence is clear that a whole food, plant-based is the best diet. I mean, it also makes common sense to eat a balanced diet to get all the different macro and micro nutritients, minerals and vitamins.
The "carb is bad!" line is just wrong. Eating one or two slices if fresh, whole weat bread is not unhealthy, it's healthy! It contains a lot of fiber, protein, vitamins and minerals. But of course, eating frozen pizza is unhealthy because it contains jackshit. Carbs != Carbs.
So why do these intermittent fasting, keto and what not diets work? Well, because people just live a silver bullet and quick fix. And many companies and people make a lot of money by selling these alleged quick fixes to people in the form of ready-made meals, books, coachings and what not.
Nobody is getting rich if people would just eat fresh vegetables.