I wouldn't expect something that stupid to understand density.  Lean body mass is around 1100 kg/m^3 while fat is 900, so it's not even that huge a difference.  Not to mention how hard it is to gain even a single pound of muscle mass. I think the natty limit is estimated at 2 pounds per month under ideal conditions. 1 pound a month with careful training and diet is more realistic, at least for an experienced lifter.