That, or one has to limit themselves and lose weight for the surgery while the other pigs out in front of them. They likely relapse and just gain all the weight back causing all sorts of internal issues. A waste of effort, time, and help... No amount of surgery will help them, they want to be a whale. Or on the rare chance  they actually get their shit together and put in the work to get back into human form, they will be dragged down by their whale partner.