Ketone body

Ketone bodies are water-soluble molecules that contain the ketone group produced by the liver from fatty acids during periods of low food intake (fasting), carbohydrate restrictive diets, starvation, prolonged intense exercise, or untreated type 1 diabetes mellitus. They are used as an alternative energy source when glucose is not readily available.

Types of Ketone Bodies

There are three primary types of ketone bodies:

• Acetoacetate
• Beta-hydroxybutyrate
• Acetone

Acetoacetate

Acetoacetate is the first ketone body that is produced in the liver during the process of ketogenesis. It can be converted into beta-hydroxybutyrate or spontaneously decarboxylate to form acetone.

Beta-hydroxybutyrate

Beta-hydroxybutyrate is not technically a ketone but is often grouped with ketone bodies. It is formed from the reduction of acetoacetate and is used as an energy source by various tissues in the body, including the brain.

Acetone

Acetone is a minor ketone body that is produced in smaller quantities. It is formed by the spontaneous decarboxylation of acetoacetate and is excreted from the body through the lungs and urine.

Production and Utilization

Ketone bodies are produced in the mitochondria of liver cells during periods of low carbohydrate availability. This process is known as ketogenesis. The primary substrates for ketogenesis are fatty acids derived from adipose tissue and amino acids from muscle protein.

Once produced, ketone bodies are released into the bloodstream and transported to various tissues, including the brain, heart, and skeletal muscle, where they are converted back into acetyl-CoA and enter the citric acid cycle to produce ATP.

Physiological Role

Ketone bodies serve as an important alternative energy source during periods of fasting or carbohydrate restriction. They are particularly crucial for the brain, which cannot utilize fatty acids directly for energy. During prolonged fasting or starvation, ketone bodies can provide up to 75% of the brain's energy needs.

Clinical Significance

Elevated levels of ketone bodies in the blood, a condition known as ketosis, can occur in response to prolonged fasting, carbohydrate restrictive diets, or uncontrolled diabetes mellitus. While mild ketosis is generally harmless and can be a normal physiological response, severe ketosis can lead to ketoacidosis, a potentially life-threatening condition characterized by high levels of ketone bodies and acidosis.

See Also

• Ketogenesis
• Ketosis
• Ketoacidosis
• Diabetes mellitus
• Citric acid cycle
• Fatty acid metabolism