I know that it’s been shown that when people do crash diets it’s ineffective because they regain the weight. Defining crash diets here as someone losing an aggressive amount of weight quickly, like 2-3% per week.
But what actually is going on when someone who weighs 200 lb loses 20 lb in 2 weeks and then regains it when they resume their prior eating habits? Do they lose fat and then just quickly regain it when they eat more? Or is it just water/glycogen that was lost and replaced?