Daughter of a spine surgeon here: They DO eat and drink, just not a meal. Nurses give them "bite size snacks", like a piece of chocolate, or some water/juice with a straw. The surgeon does not touch the food, the nurse gives it to them, and this keeps them going till the end of the surgery. However if they know they have a long surgery ahead they will eat and drink well before going to the surgery room. They also DO go to the toilet if they really need to. Even though surgeries do have critical moments in which everybody must be concentrating at 110%, there are also moments that are a bit less "critical", and these are the moments where they can go for a quick pee or take the snack from the nurse (bare in mind there are usually more than 1 surgeon so the other one can keep things stable and safe). They try to hold if they can, and rarely go number 2, but if they have an emergency diarrhoea they must go, simply because it would not be safe for the patient if the surgeon is performing a delicate operation while having massive cramps :/ in those cases is best to just quickly go to the toilet and come back.