The real secret is all to do with your carb intake. However you do it, however strict you are, it's an inescapable fact that carbs are what make you fat. It's to do with your insulin production. The best bit of advice is to replace whatever carbs you cut with fat. Good healthy fat like Coconut oil, olive oil, butter, fish oil, eggs etc and not vegetable oil or trans fats etc. That way you won't catabolise and your own muscle.