As someone who can gain weight by just inhaling too deeply as I walk past a bakery, I know packing on the pounds do nothing for my breast size. It's like everything else but.
It took this old fart about 3 years to get to about full size, a for real A to a small B. Having been a former fatty and God only knows what other reasons, like perhaps Klienfelters, I was always a tad gynocomastic, as in sub AA but still there plain as day.
With my almost leveled off size, I can not absolutely say adding P helps, but I do seem a lot more full and my wife complains a lot more about the girls being noticeable when I'm in guy mode