Which fats are consumed first in a starving body?

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Offline thedoc

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ünsal Erdem  asked the Naked Scientists:
My name is Unsal from germany

I am not sure this is the right place to ask but i have a question for you.
I was wondering in deficiency of energy (glucose) we start to breakdown fatty acids. My question is "do our bodies use old stored fat acids or the ones that were stored recently(new fat acids)"

What do you think?
« Last Edit: 03/05/2013 09:30:01 by _system »


Offline chris

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Re: Which fats are consumed first in a starving body?
« Reply #1 on: 04/05/2013 11:04:02 »
The first thing a starving body consumes is glycogen in the liver and muscles. Through the process of glycogenolysis, the molecule is broken up into glucose-6-phosphate units that can be fed directly into a cell's metabolism. The liver (but not muscle) also has a glucose-6-phosphatase which can produce pure glucose molecules again that can be released into the bloodstream to top up blood sugar.

When the glycogen runs out, fat metabolism (lipolysis) switches on under the direction of hormones like adrenaline, glucagon and a drop in insulin. Lipases in adipose tissue break up the stored fat, which is

The process of beta-oxidation is activated in adipose tissues. This chews up the fats stored in the cells releasing glycerol and fatty acid molecules, which are released from the cell and transported to the tissues in the bloodstream. Taken up by "hungry" cells, the fatty acid molecules are chopped up and fed into the metabolic pathway within the cell at the Kreb's Cycle stage.

But to clarify your last point, there is no strict "pecking order" for fats being broken down within cells and then consumed within other cells. The body does not label the fats with "best before dates"; that said, not all fat stores are mobilised and access equivalently rapidly. The fat stored in the viscera - abdominal fat - tends to be deposited early and removed late. There's clearly something different, biochemically, about this storage site, hence its link to atherosclerosis, but exactly what, we don't know.
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