I’m not sure I would do a full fast post surgery. I would think you need nutrients to heal. But what about looking up the immediate post-surgery diet for a stomach altering surgery? Either VSG or gastric bypass. At least you would know that those patients also had surgery and are still able to heal but also lose a lot of weight. Focus on protein. Seems like your body might need it at the moment. I’m sure others here will have better information, that’s just a suggestion from a slightly medical perspective but only a nurse so not a doctor or anything.