I've read that very low carb diets such as Atkins, CDK, South Beach Phase 1, actually help prevent muscle loss while restricting calories...compared to just restricting calories alone. If you are taking in enough calories you should not lose signifiacnt lean mass while on a low-carb diet...as long as you keep training. You probably won't gain lean mass very fast though...the right carbs at the right time can really halp put on muscle.
JoBu