People I live with have noticed that my breath smells heavily of acetone. This is symtomatic of ketosis. It is induced by a lack of glucose, and the body reverts to burning stored fat for energy. The resulting excess of fatty acid in the bloodstream causes the scented breath.
Supposedly, being in this state burns fat -- and so long as you eat plenty of protien, will maintain muscle.
Now, what is the opinion here on training in a state of ketosis?