You shouldn't eat anything before you go to hospital.改为同义句

可惜楼主没有提供变化格式,所以只能多写几种,以供选择：
You shouldn't eat anything before you go to hospital。
= You should eat nothing before you go to hospital。
= You ought to eat nothing before you go to hospital。
= You are supposed to eat nothing before you go to hospital。
= You oughtn't to eat anything before you go to hospital。
= You aren't supposed to eat anything before you go to hospital。
注：should do sth = ought to do sth = be supposed to do sth 应该/应当做某事