Ketone Bodies

Ketone bodies are organic molecules which contain the carbonyl group, C=O. In the human beings and the rest of mammals, they are the metabolic products of lipolysis and ketogenesis. The former pathway is the breaking down of fat or triglycerides into fatty acids and glycerol, while the latter one is the metabolic conversion of fatty acid by the liver cell mitochondria into ketone bodies: β-hydroxybutyrate, acetoacetate, and acetone.

Except for acetone, they are used as fuel by most of the body cell mitochondria for the production of ATP in the Kreb's cycle and in the electron transport chain of mitochondria. Ketone bodies production takes place in the absence of carbohydrates as when we are on a ketogenic diet, also during fasting and/or when we have worked out hard for more than 30 minutes and we are burning fat.

To summarize, the fat contained in the food we eat, or the fat in the form of triglycerides in our adipose cells, is metabolized (burned) into β-hydroxybutyrate, acetoacetate, and acetona, with the first two ones being used as fuel. This metabolic state is called ketosis. We must not confused it with ketoacidosis, which takes place only in diabetic people.

Ketone bodies are so small that they can cross the blood-brain barrier as they are employed by either pyramidal neurons or oligodendrocytes. Red and white blood cells, however, can not use ketone bodies as fuel because they lack mitochondria; they only consume glucose.