As mentioned elsewhere, prior to surgery, the person should be taking extra care not to put on additional weight. Maintaining a healthy diet and moderate exercise to the extent possible would be beneficial.
Post surgery, while in the hospital, the patient will be put on a special diet that is individually catered based on the patient’s pre-existing conditions. A dedicated dietician and nutritionist will be monitoring to ensure the patient is getting the required nourishment. At discharge, the dietician may recommend following a specific diet to improve overall recovery.