How does the body create glucose for the brain when the body isn’t taking in any carbs?
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It uses a process known as “gluconeogenesis” – which basically just means “creation of new glucose”.
To create glucose the liver needs some other compound that it can convert to glucose, and it unfortunately can’t do it with fat.
There are three compounds it can use:
1. When fat is being burned, the body breaks apart triglycerides into three fatty acids + glycerol, and the glycerol is converted to glucose.
2. If more glucose is needed or there are extra amino acids around, the body can convert *most* amino acids into glucose. This is what is happening when people who are on a diet lose muscle mass – it gets torn down and converted to glucose. This is also what people are concerned about after long exercise sessions.
3. Glucose can be partly burned and converted into lactate, and the lactate can be converted back to glucose, though it takes a lot of wasted energy to do that.
Note that if there are no carbs coming in, the brain can’t burn fat because of the blood/brain barrier. The liver does the first part of fat burning, creates ketones, and the brain completes the process of burning fat.
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