I've noticed that as you become "keto adapted" you get less ketones coming out.
Obviously if you're eating massive amounts of fat, your body will be excreting lots of ketones. But when fasting and your liver has been emptied your ketone production will be nicely controlled by your body. It only uses what it needs, and most ketones are going to be burnt and not excreted.
So fasting wont get you to ketoacidosis. Partial eating could.