What dose of Abilify will you be taking? Unlike most antipsychotic meds, abilify has dose-dependant effects at the D2 receptor.
While there is a lot going on with these medications, antagonism at D2 is responsible for a lot of the nasty bodyweight and body composition side effects of antipsychotics.
At low doses, abilify is a partial agonist at D2 (this is good). This is why some people find it to be stimulating. Here it's acting sort of like a Parkinsons or RLS med, or if you've read Lyle's book by the same name, like Bromocriptine.
At higher doses its activity seems to flip from agonist to antagonist (this is bad). This change in activity is consistent with the anecdotal reports of people taking high doses and gaining weight.
What's high doses and low dose? I don't know for sure, but I certainly found 2.5 and 5.0mg to be quite stimulating and didn't gain any weight. There seems to be a ton of individual variation here anyway.
Otherwise, and as I'm sure you know, there are a plethora of different options out there. Abilify even has a new and improved younger brother whose name escapes me at the moment. If you are experiencing intolerable weight gain, bring that up with your doctor and try a new med.
All the while, the basics of a sound diet and exercise routine still apply.