This topic has probably been done to death....

I am wondering why you have to eat sooooo much when you go on programs that are designed to add alot of muscle. I have never heard any scinece behind this. My goal right now is to increase muscle mass which is why I am doing 20 rep squats right now. However, I would really love to loose fat at the same time. I don't quite understand why this is not optimal? Can anyone cite some research for me?