The concentrations of acetoacetic acid, b-hydroxybutyric acid, and acetone occasionally rise to levels many times normal in the blood and interstitial fluids; this condition
is called ketosis, because acetoacetic acid is a keto acid. The three compounds are called ketone bodies. Ketosis occurs especially in starvation, in diabetes mellitus, and sometimes even when a person’s diet is composed almost entirely of fat.
The acetone that is formed during ketosis is a volatile substance, some of which is blown off in small quantities in the expired air of the lungs.This gives the breath an acetone smell that is frequently used as a diagnostic criterion of ketosis.
When changing slowly from a carbohydrate diet to an almost completely fat diet, a person’s body adapts to use far more acetoacetic acid than usual, and in this instance, ketosis normally does not occur.