In ketosis, the body produces ketones; they are chemicals produced by your liver. Your liver produces this chemical because it lacks enough insulin in your body to convert sugar into energy. So the other source of energy the body turns to is Fat. Your body(liver) turns the Fat into ketones and sends them down the bloodstream.
Do you get? So these ketones which are released by your liver is what makes or causes the odor oozing from your breath whenever you are starved, on fasting or on a weight loss diet.