Everything you do after the fast, especially immediately after, will effect you. If you just dive into eating, it'll just undo everything you did while fasting. One book I read on JFing said it like this, "when your done with your JF it's like waking a sleeping giant." Your biggest job will be controlling the giant so as not to destroy everything you just did.
You'll regain some weight because your body is holding fecal matter and water again (due to salt intake) but other than that, IF you eat healthy, you should be able to maintain.