Am not banded but know the physiology:
Fat has an enzyme called 'aromatase'. This enzyme will convert testosterone in your body to ESTROGEN! So, the more fat you have, the more aromatase you have and that means more estrogen than the average lean mean. With weight loss, the testosterone/estrogen balance changes to favor the man hormone. This means all those things we like: increased muscle mass, increased energy, increased sex drive, and a bigger cock. (I'm LOL, I had to say it.)
[The penis responds to testosterone, so with a better balance it would gain more tissue in theory.]