How to lose weight without losing muscle mass?

if you mean u wanna lose fats......then u got to strictly stick with protein shakes in breakfast, lunch with light dinner......very less carbohydrates and no fats..........as you know that protein is difficult to digest and lot of energy is required to digest it which is taken from fats n carbhyd.........if you dont include this in ur diet then body will utilise existing quota from ur body.......thus max fats will get burnt from ur body....but i advise you not to take excessive protein which is not good for kidneys unless u heavy gym....take note that too much protein shuld nt be found in urine.