So far all current knowledge is saying to increase mass you need to eat a surplus of kcals for tissue growth. Even trainers that follow Paleo nutrition protocol are still advocating this, ie. Dan John, Charles Poliquin, etc..... That's not "calories in , calories out". It's just common wisdom.
I think as Paleo increases through out the athletic world someone may do a study on metabolic efficiency.
There's room for you to experiment on this.
