Crash dieting is something we see time and time again. It really does work and you will lose a lot of weight in a short amount of time, Great right? Not necessarily, unfortunately within that weight loss you lose a lot of muscle as well as fat tissue and hydration.
This is due to having to lower calorie consumption and being in too bigger deficit , muscle wastage is part of the weight loss outcome.
Consistent realistic weight loss goals are much better for longevity , as you keep your lean muscle tissue up and reduce body fat percentage, this strategy is even more effective with exercise specifically weight training.
In theory the more lean tissue you have, the more calories your body uses, realistic weight loss goals are essential for progression that lasts.