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Ketone body metabolism
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ketone bodies in p. 88
ketone bodies p. 88
In life, it’s helpful to have a plan B in case plan A doesn’t work out.
But if these main fuels aren’t readily available, then plan B is to use an alternative fuel source - ketone bodies.
Ketone bodies are a group of carbon-containing molecules produced by liver mitochondria using a 2-carbon molecule called acetyl-CoA.
Ketone bodies can be released into the circulation and get picked up by the majority of cells.
Inside the cells, they’re reconverted back into acetyl-CoA, at which point they can then enter the mitochondria and produce ATP.
The 3 primary ketone bodies are acetoacetate, beta-hydroxybutyrate, and acetone.
Alright, so let’s say you decide to go on a 5-day fast.
About 12 hours into your fast, your blood glucose levels start to dip.
Then, around 1 to 3 days into your fast, your body begins to run out of the necessary substrates to make new glucose.
So, it switches to breaking down fatty acids for energy.
Fatty acids are mobilized from fat stores and are broken down to acetyl CoA through beta oxidation in the mitochondria of most cells - except for brain cells.
Ketone bodies like beta-hydroxybutyrate and acetoacetate are an alternative source of energy in states of prolonged starvation. Ketone body synthesis occurs in the liver in physiologic states like prolonged fasting or exercise, as well as in pathological states like type 1 diabetes mellitus or alcoholism. Once synthesized, ketone bodies can leave the liver, and enter into peripheral cells such as the brain, skeletal muscle and kidney to serve as energy sources.
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