here's what i like to think the ivs/evs would contribute to (1st thing affected most):

HP: belly/balls
Atk: muscles/longer cock
Def: butt/thighs
Sp. Atk: pecs/moobs/thicker cock
Sp. Def: overall weight/thighs
Spd: thinner waist/increased stamina

tried to balance them out but theyre def not perfect