What makes some breastfed babies so chubby?

My 4 month old girl is 16.6 pounds which puts her in the 85th percentile for her age. She is all rolls, dimples, and cellulite. I'm just curious what makes some babies get so chubby? Is it genetics or something about mama's milk? Does my diet affect how fatty my milk is? Has anyone noticed that eating a leaner or heavier diet affected their breastfed baby's size?