Some people with liver disease must eat a special diet. This diet helps the liver function and protects it from working too hard. Proteins normally help the body repair tissue. They also prevent fatty buildup and damage to the liver cells.
Advise is a verb, and advice is a noun. So advice is what is given, while the act of giving advice is called advising (or to advise).
For me, please advise must include a specific request for instructions and implies that non-response is not an option. I get rather annoyed when someone uses it without specifying what information they want or, worse, when they don't want any information at all.