T Nation

How Does Protein Turn Into Fat?


#1

If you can turn carbs to fat, fat to sugar, protein to fat then to sugar then why can you not turn fat back into protein?

If excess protein is stored as fat, where do all the amino acids 'magic' away to? By what process does this happen and why can it not happen in reverse?

Where did all the aminos go? Are they hanging around somewhere for future use? Are they in the stored fat?

Did David Blaine take them away?

http://www.exploringwomanhood.com/mindbodysoul/weightloss/excessprotein.htm

Ha ha - I just happened across that site when googling for "protein to fat"


#2

I could be wrong, but I believe it has to do with the nitrogen atoms in the amine group that give amino acids their name. If they convert to carbs or fats they are stripped of this nitrogen. Thus its a lot easier to go from pro -> fats or carbs than it is the other way around.

does that sound right to anyone else, or did I just make that up in my head?


#3

You're one the right track.

Once the amino groups are removed, the carbon skeletons of amino acids can be broken down further to...

1)citric acid cycle intermediates, which can then go on to form glucose
2)Acetyl CoA and acetoacetate, which go on to form fatty acids and ketones.

The OP mentioned going from fat to sugar. This does not happen, to my knowledge, as humans lack an efficient way of going from Acetyl CoA, a product of beta-oxidation of fatty acids, to glucose. (Can't go from Acetyl CoA to pyruvate I believe.)


#4

I don't think fat can be turned into glucose, but i could be wrong... But protein can be turned into glucose, that is for sure.

Fat does got to free fatty acids and free fatty acids can be turned into ketones.


#5

fat can not be turned into glucose


#6

... and ketones can be used for most of the things that glucose is used for, right?


#7

Yes, but glucose is more efficient and therefore gets priority in metabolism if present(disclaimer: could be wrong).

Newdamage: Sounds right to me. Glycerol from triglycerides can be converted to glucose but pyruvate to acetyl-CoA is irreversible as the carbon atom is lost.


#8

AFAIK, excess amino acids are broken down as part of the ornithine cycle to produce urea, which is then excreted in the urine. So to answer the OPs question, the excess aminos are not lurking waiting for their chance to one day rise again. They have been broken down and lost.