We all have that friend who occasionally runs on a cool 700 calories a day for a week so they can ~lose weight fast~ or whatever.
That’s a crash diet. As in, it’s pretty much bound to crash and burn.
Your metabolism slows WAY down, so you suck at burning calories.
And then you start to burn off muscle.
You're hungry ALL the time.
You become kind of a monster.
Moving at all sounds like a chore.
Your sympathetic nervous system gets lazy.
You miss out on major nutrients.
OK, sure, you'll probably lose weight. BUT keeping it off is no guarantee.
And post-crash... no one's totally sure what might happen.
Bottom line: Crash diets might be a quick fix, but they can also be awful, dangerous, and come with lasting negative health effects.