unless you´re a boxer triying to go down 2 weight classes i highly doubt a diet will kill you ,besides you don´t have to eat a plate of salad every day you can start by changing small things like eat less fast food, exercise on a daily basis, etc the idea that you can´t change your weight permanetly is dumb and unfounded
First of all, I never said that dieting will kill you, I said that if you're always on a diet that actually works, you will continually lose weight until you become anemic and underweight. "Dieting" means managing your food intake in such a way that you lose weight, you're supposed to stop dieting after hitting your goal weight and instead switch to a life-and food style that keeps you at that weight without gaining or losing weight in general.
No one has claimed it's impossible to change your weight, the issue raised was that diets are usually bullshit because they try to sell you the idea that "just do this for a few weeks and you're done" when in reality, you then have to also change your entire lifestyle permanently to one that can maintain you at that weight. Going back to what you were doing before dieting will just get you overweight and in need of dieting all over again, which conveniently means you're back to giving money to the people trying to sell you dieting bogus.
A lot of dieting manga have this flaw, where they will introduce a diet that works for the character but then once they hit their weight goal they just stop and go back to the same behaviour as before, only conveniently they don't gain the weight back because fiction doesn't have to follow rules. Not saying all dieting manga do it, just that it's usually a good sign that the author is writing about something they probably don't really know much about.