I'm 5'3" and 152 lbs. I've recently begun to rotate my caloric intake between 2-week periods of extreme deficit, moderate deficit and maintenance.

During the extreme deficit periods, I stick to a vegan diet since it allows for a greater volume of food; however, I'm very careful to keep my protein intake between 35-50 grams. I'm allowed 1200 calories/day during this period, but so far I really only manage about 1050 calories.

I know the main concern with extreme deficit diets is a breakdown of existing muscle for fuel in order to meet the body's protein requirements. Since I'm still consuming a reasonable amount of protein, is this really a concern for me?

That's very nice. But if you don't eat enough your body will hold on to what little food you give it. This will make losing weight difficult, and increase your risk of gallstones and gout. Very low calorie diets often make you feel hungry and deprived, thus causing you to quit dieting and binge.

Well to maintain your self healthy and fit then it is very important to have a balance diet and workout , low calorie diet is also play an important role to loss your weight ,but your need to workout regularly to maintain you your muscle mass..