How does the body create glucose for the brain when the body isn’t taking in any carbs?

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How does the body create glucose for the brain when the body isn’t taking in any carbs?

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It can release stored glucose, if any, but if the body isn’t taking in any more carbs and the glucose level gets too low, the body is going to go into a seizure.

The body can metabolize both fat and proteins into glucose for energy. It takes different pathways and metabolisms, and the direct use of carbohydrates are “preferred”.

The exact chemistry is complicated, but just know if the body can’t find free glucose for energy it can shift into fat based, or protein based metabolisms for energy. This is exactly how low carb diets function.

EDIT – When I say “preferred” I’m not making a medical or health recommendation/statement. I’m just saying that given a supply of both, the body will metabolize carbohydrates before it starts to metabolize fats and proteins.

Your body stores carbs in the muscles as glycogen. Your liver stores fructose which can be converted into glucose. Your body can convert fat into energy as a separate fuelling system. Your body can also convert protein into fuel. Carbohydrates is just one way of fuelling yourself, it’s what we are most comfortable with and it’s fairly cheap and sustainable thus the preferred method across the world

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.