No I've not gone through Pluto trine Sun, but once you have transformed via a Pluto transit, you most likely will not go back to the way you were before. If Pluto is to be attributed to your empowerment in deciding to loose weight, it is up to you also to maintain the same lifestyle change that has happened as a result of the transit. Pluto sweeps away old things, habits, beliefs that are no longer any use for us, once they are gone, they are gone. Its more than likely that this is a permanent change, but it is up to your free will too to keep it that way.