I think if carbs were dropped for a long time to nearly zero, there would be immediate muscle and lean tissue wasting, not to mention a weak immune system (lack of glutamine). If carbs were suddenly added in high amounts, there might be a higher than average amount of muscle synthesis, due to the body's adaptation to no/low protein. The body may also put itself into a state of low catabolism. It's called protein cycling, and it doesn't seem to be very effective in improving one's physique unless it is done in a more moderate fashion.