Because of the parsnip-like taste and musty smell, it isn't easy to sneak hemlock into ice cream. And the paralysis of the tongue it causes would likely lead more to weight loss than weight gain. [And, would impact her oral skills as well].
The weight gain may seen as verification of her recent lack of meth use, an destructive habit of which Mia is often accused as well.
I also tend to prefer Ava over Mia, though it is likely because her hair, eyes, skin and slightly slavic look make her appear like a Czech assistant I lusted for. So though I would be "doing" Ava, it wouldn't even be Ava I was thinking about.
I find both sisters highly attractive and would enjoy to participate in multiple Cherish/Cali Marie like P2Ms between them.

Have to have $250k to lose to start my own porn company, though.
- Lame-ass Rose Sisters Fanboy who knows Mia's rescued dog's name is "Noah"