Can Ketone Bodies Be Converted To Glucose?

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Ketone Body Metabolism

Ketone body metabolism includes ketone body synthesis (ketogenesis) and breakdown (ketolysis). When the body goes from the fed to the fasted state the liver switches from an organ of carbohydrate utilization and fatty acid synthesis to one of fatty acid oxidation and ketone body production. This metabolic switch is amplified in uncontrolled diabetes. In these states the fat-derived energy (ketone bodies) generated in the liver enter the blood stream and are used by other organs, such as the brain, heart, kidney cortex and skeletal muscle. Ketone bodies are particularly important for the brain which has no other substantial non-glucose-derived energy source. The two main ketone bodies are acetoacetate (AcAc) and 3-hydroxybutyrate (3HB) also referred to as β-hydroxybutyrate, with acetone the third, and least abundant. Ketone bodies are always present in the blood and their levels increase during fasting and prolonged exercise. After an over-night fast, ketone bodies supply 2–6% of the body's energy requirements, while they supply 30–40% of the energy needs after a 3-day fast. When they build up in the blood they spill over into the urine. The presence of elevated ketone bodies i Continue reading >>

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  1. Doug Freyburger

    Others have mentioned the chemical details that lead to limits. That's only one side of the story. The other side is redundancy in energy production. Ketones can be used in anaerobic energy production. It's not as efficient but it is faster. There are times when fast beats efficient so redundancy gets selected for.

  2. Anand R

    Acetyl CoA can’t be circulated for two reasons: it’s a high energy compound and it’s labile. So it’s not a stable form for circulation to tissues. Also acetyl coA cannot cross cell membrane.
    Ketone bodies are an alternate fuel source. More importantly, they are water soluble analogs of fatty acids. This is important since, during starvation there is fat breakdown and excess fatty acids circulate in blood. However, fatty acids cannot be used by brain as fuel since, they cannot cross the blood brain barrier. Liver by producing ketone bodies helps brain cells during starvation.

    Also, these ketone bodies, as such, can be used by other tissues as well. There by other tissues refrain from using glucose. Hence, ketone bodies have a glucose-sparing effect. This glucose will be available for tissues like brain and red cells for use.

  3. Barry Gehm

    It’s because oxaloacetate is needed to metabolize acetyl-CoA (first step in the Krebs cycle is the reaction of acetyl-CoA with oxaloacetate) and is also needed (and used up) in gluconeogenesis (the production of glucose from amino acids and other small molecules, but NOT from acetyl groups or fatty acids). The liver is primarily responsible for gluconeogenesis, and if it uses up oxaloacetate on that, acetyl-CoA builds up and ties up all the coenzyme A in acetylated form. In order to alleviate this, the liver converts the acetyl-CoA into ketone bodies, and releases them into the blood. These, as the book says, are taken up by other tissues (such as brain and muscle) and converted back into acetyl-CoA. A key point is that these cells can use the acetyl-CoA because they are not depleted in oxaloacetate because they do not carry out gluconeogenesis.

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