No, I have read of people going on extended fasts... carbs, calories and everything zero, and they do not lose scale weight.

Our bodies are amazing but they are not "machines". Your metabolic functions are quite different from mine and everyone else on this forum. Your age, length of time you were obese, genetic predisposition to body shape, activity now, etc. You have been on this forum for two years now and you appear to be very successful and healthy...a 6 foot, 211 pound muscular guy. A goal of a 21 BMI seems unrealistic whether you are eating 5 or 25g carbs. Severe calorie restriction might get you there...but Why? Especially when you have asked many questions mostly in various forms of how can you add back processed SAD carbs.

Since you want to build muscle while eating good food on the low carb end of the scale, you might also want to check out Dr. Ted Naiman's information of diet and exercise: http://www.burnfatnotsugar.com He has super simple MEAL plans and exercise routines, a recent version is eat steak and eggs, add some green vegetables now and again.

Remember Dr. Phinney's advice: " If you want my secret to the right weight goal...it's the weight you can get to without too too much of a struggle and when you get there, still have a life, and you have to find that out by experience. I cannot give you a destination and GPS coordinates to get there."