metal mouth
Until you are no longer in ketosis
Ketosis is the bodies way of surving starvation..which is esentially what we are doing by having this surgery. It is a change from a carb driven metabloism to a fat based one.
What happens is your body uses fat in the liver to create ketones and the ketones are used as fuel by the various systems in your body. If there are not enough ketones, your bod breaks down stored fat to use to make more. The great part is, if you do not use all the ketones your body flushes them out instead of storing them back as fat (which is what would happen otherwise). The bad part is, excess ketones make your breath and urine stink.
You can beat this though.. the key is to excersize more until you use up the ketones or drink so much water you dilute the extra ketones in your urine enough to take out the stink. The first is more preferable
Further reading:
Wikipedia: http://en.wikipedia.org/wi****tosis
Or "The Ketogenic Diet" by Lyle McDonald