abcs-
eating protein is good to maintain muscle and develop muscle, just remember that at some point, your body doesnt use excess protein and you piss it all out.
generally you need 0.8 grams of protein per kg of body weight.
for example someone that weighs 200 pounds is about 91 kilograms (because 2.2 pounds per every kilogram)
then multiply 91 by 0.8 will give you about 73 grams of protein.
so someone that weighs 200 pounds should eat about 73 grams of protein per day.
but this is for a regular person.
if youre doing cardio and weight lifting, you can multiply by as much as 0.9 or 1.0 instead of 0.8.
also remember that building muscle mass and resistance training is a good way of losing fat too....it takes a lot of calories to repair torn muscles from weight lifting.