Eating five pounds of skinless chicken breast is a immediate way to increase your lean mass by five pounds. You can confirm this either by a water displacement or DEXA scan.
How do you increase your lean mass by eight pounds? That's right, eat eight pounds of skinless chicken breast. Twenty five pounds? Twenty five pounds of chicken breast.
Basically, chicken breast is a one-to-one map for lean mass. Technically, you don't even have to eat it...just carry it around with you, like in your pockets and stuff.