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Old 10-09-2003, 01:01 PM   #1
Paul Kayley
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Rob, wanted to call upon your Biochemistry expertise. I am trying to get to grips with energy production as a fat-adapted athlete.

As I understand it at the moment fats are oxidised in the mitochondria via beta-oxidation, while carbohydrates are oxidised via the TCA cycle. The oxidation of FFAs being reliant upon the availability of glucose (from plasma, glycogen, and gluconeogenesis from glucogenic aminos) Is it an over simplification to say that fat must burn in a carbohydrate flame?

How does glycerol from triglycerides fit into this to keep the TCA cycle going?

In what sort of proportion or to what extent is glucose needed to support beta-oxidation?

I have read that glucose can be produced from fats in the liver. I didnt know that this was possible...unless the glucose is being derived from the glycerol portion rather than the fatty acid portion?

I have also seen that ketone bodies enter into the mitochondria to contribute to energy production in some way. How do they do this?

Can ketones provide energy to support the TCA cycle and fill in the gaps left by glucose to maintain beta-oxidation of fats?

I understand that the brain, renal cortex, and other peripheral tissues can use ketone bodies as an alternative to glucose for energy, and it is even proposed that these organs even preferentially use ketones over glucose when there is a consistent and dominant supply. How do ketones provide this energy?

Sorry for so many questions. Thanks Paul
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Old 10-10-2003, 05:14 PM   #2
Robert Wolf
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Paul-

Beta fatty acid oxidation produces two carbon units which can then be plugged into the TCA cycle as acetyl-coA.

http://www.gwu.edu/~mpb/betaox.htm



In the presence of adequate carbohydrate FA's are metabolized to C02 and H20. As carbohydrate enters the TCA cycle as a 3 carbon molecule forming ultimately oxaloacetate, it is added to the two carbon molecule of acetyl-coA forming citrate. If Carbohydrate is lacking the TCA cycle can not function and the acetyl units are formed into beta-hydroxybutyrate.

Here is a great desctription of all this...ketosis is explained near the bottom:
http://www.indstate.edu/thcme/mwking...oxidation.html

I'm not sure HOW ketones provide energy...the text seems to imply that they are formed into four carbon units and then cut back to acetyl units...that is still not going to work for the standard TCA cycle, so I'm not sure unless gluconeogenesis provides oxaloacetate via amino acids...probably the case as there are not other pathways!

Here is a good site as well but it is ironic that they know the mechanisms of the science yet draw the same wrong conclusions as the rest of the world:

http://www.np.edu.sg/~dept-bio/bioch.../aab_lipid.htm

The only contribution fats can play to glucose production is glycerol...really minor all things considered. this is illustrated at the top of the last diagram.

Glucose acts in a semi catalytic fashion in the TCA cycle...I forget the ecact ratio but you get a lot of milage out of each glucose molecule with regards to supporting the oxidation of fatty acids.

If i missed something, let me know!
Robb
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Old 10-11-2003, 02:16 AM   #3
Paul Kayley
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Thanks Rob, very interesting stuff. I am hoping that the key is to recognise the potential of glucose more as a semi-catalyst rather than a primary fuel source.

Have you encountered any research or literature which can shed light on what aspect of endurance training actually stimulates mitochondrial density increases? Is it simply a response to prolonged and elevated metabolism of the cells involved; or is it more likely to be a response to depleting glucose stores and therefore a need to glycogen-spare by increasing mitochondria numbers, so that each can work at a lower rate per workload and therefore use a greater % of fats thus sparing glucose?

Cheers PK
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Old 10-11-2003, 05:04 PM   #4
Robert Wolf
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Paul-

I have NO idea wha the direct stimulus is. Many, many factors occur in long term adaptations, for example increased lactate shuttle efficiency. Have you read the time cours of training adaptions Coach has refrenced previously? Look in the archives and /or the free CFJ. if I remember correctly some of that is discussed.
Robb
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