Diet for newly diagnosed father

My father was just diagnosed with PC after an incidental finding on a chest CT scan. It has yet to be staged but it appears from the endoscopic ultrasound that the cancer has not yet spread outside the pancreas, even though the tumor is pretty large (4cm). He still has no symptoms but the tumor is very close to both the hepatic portal vein and common bile duct. Do any of you know of any dietary guidelines for PC that he needs to be following at this point. What changes to his diet need to happen if he has surgery and/or chemo?