I'm on a two week liquid optifast diet pre-op. There are medical reasons for this... first and foremost is that this diet will shrink my liver and spleen so that it's easier for the doc to access everything during surgery. Also, I've recently been told that a fatty liver is much more fragile. That's one reason that many docs require a pre-op diet.
Another reason is to see if you really can stick to a new way of eating. If you cheat during the two weeks, it's less likely that you'll be able to make the changes needed. Other docs require that the patient lose from 1 to 2 percent of their weight prior - same reasons listed above.
If I were in you're shoes, I'd run right out and get some sort of meal replacement drinks and stick to them. Optifast allows 5 drinks a day - actually, that's requires 5 drink a day. You could also do bullion and sugar free jello. Today is day 5 and I've already lost 10 lbs!!!
Best of luck to you! See you in Band-land!

Barbara