A person is undergoing prolonged fasting. His urine will be found...

The fat when burned to the energy, it releases many ketones in the blood and so urine. This process of producing energy by the fats is fat acid catabolism. Hence a large amount of the ketone gets eliminated in the urine causing ketonuria. Related Theory A condition in which abnormally high amounts of ketones and ketone bodies (a by product of the breakdown of cells) are present in the urine is called Ketonuria. It is a sign seen in extreme case of diabetes mellitus.