If you stick o it you can expect about a stone a month. You want to know about side effects and water, potential effects on periods and medications. Your consultant should explain everything. And son be afraid to ask questions either during or after (she'll give you her contact number etc) no question is silly!
As a bit of advice stick to shakes to begin with, those on the spag Bol and bars seem to lose slower initially. Drink about 3litres of water a day and don't be afraid to have paracetamol if you get headaches. The first 3-7 days are the worst until you are in ketosis. Your consultant may give you ketostix so you can check when you hit ketosis. But you should stop feeling hungry and might even start feeling elated! If you must cheat cheat with protein like a boiled egg or low fat and salt ham! If you like fizzy drinks have a can of coke zero (not diet coke) as a treat!
Good luck!
Xxx