ketosis is recognizable by the smell of acetone (as in nail varnish) on the breath. It occurs when the body's processing of nutrient materials for the release of energy depends predominantly on the use of fats. In the absence of a dietary carbohydrate supply for maintaining blood sugar, or if sugars cannot be utilized normally, fuel must come from stored fat and muscle protein. This can occur in previously healthy people during prolonged fasting or starvation, after persistent vomiting, or on a very high fat and low carbohydrate diet; or it can occur because of disordered hormonal control of metabolism in diabetes mellitus. The high rate of breakdown of fatty acids by the liver produces the ‘ketone bodies’, acetoacetate and b-hydroxybutyrate, which are released into the blood. Some of the acetoacetate is converted to acetone — another ‘ketone body’ — mainly in the lungs, and this becomes noticeable on the breath.

The physiologically useful consequence is that ketone bodies, which are made only in the liver and exported from it, can be used by other tissues for energy production. During starvation even the brain, which normally uses only glucose, can adapt to utilizing ketone bodies.

In diabetes, the fault lies in the absence of the effects of insulin. Normally, this hormone acts to restrain mobilization of amino acids from muscle protein and their conversion to glucose in the liver, and to restrain the mobilization of fatty acids from lipid store in adipose tissue. Without this restraint, the liver not only overloads the blood with glucose, which most other tissues cannot take up and use without the action of insulin, but also overloads the blood with ketone bodies as a by-product of its excessive use of fatty acids. If the condition is uncontrolled — as it used to be before the days of insulin treatment — increasing ketosis leads to progressively more harmful acidosis, diabetic coma, and death.

Sheila Jennett

ke·to·sis / kēˈtōsis/ • n. Med. a condition characterized by raised levels of ketone bodies in the body, associated with abnormal fat metabolism and diabetes mellitus.DERIVATIVES: ke·tot·ic / -ˈtätik/ adj.

ketosis (kee-toh-sis) n. raised levels of ketone bodies in the body tissues, resulting from an imbalance in fat metabolism. Ketosis may result in severe acidosis. See also ketonuria.

ketosis High concentrations of ketone bodies in the blood.