Received medical wisdom -- or at least it was when I went to med school -- is that it takes three days of complete carbohydrate starvation to start burning ketone bodies and therefore have your breath smell ketotic.
That is some diet! Good idea to fly when on that kind of extreme regime?
QDM
QDM - is it possible that substantial exercise not long before the incident could have increased/caused the burning of ketones?
I take prodigious amounts of exercise, and am quite skinny, and a urine test showed ketones present. The advice in my case was to eat more carbohydrate.
It's quite possible that the subject was on a no carbs diet and exercising to accelerate the weight loss.