All diets are ultimately fads. The majority are and have been unsicentific nonsense, and the markedly effective ones are sometimes unsustainable, or in some cases literally dangerous. Even when they achieve the things they set out to, the goalposts tend to move on the purpose - weight loss versus muscle gain etc. So Keto is a fad, but aspects of it will be sustainable for some dieters - and it may be a focused too for certain types of folks to achieve certain types of goal. I'm old and this has been a non stop thing since the 1970s, with the "F-Plan" and "Atkins" and a few other temporary standouts.
The only thing that hasn't changed in that whole time is that a balanced diet with lots of fiber, protein and low in certain fats, is good for you. But even then the FDA and other organizations have adjusted earlier advice. And your goals may not match the value of a balanced diet. When I was young, an egg was basically a hand grenade full of instantly lethal cholesterol. It's also subjective relative to your body's chemistry and metabolism.
But celebrity diet and exercise mavens are some of the last people you should listen to. Jillian Michaels has an amazing body because she has a trainer and a nutritionist and may have a personal chef or at elast domestic help to make some of her own recommendations viable in a way that's absurd for non profressionals to consider, in terms of time, cost and effort.
Reminder, Robert Atkins, creator of the eponymous low carb diet, passed away after slipping on ice and suffering a severe head injury. So while low carbs sounds good, it appears it can end in fatal brain injuries and skull cracking.
If you want to lose weight and build muscle tone and maintain that, then the best advice is to be a multimillionaire in the public eye with lots of free time and a mania for exercise.
And remember that electrolytes are what plants crave.