On Jan 16, 2006, at 8:49 pm, Todd Moody wrote:

> Ashley Moran wrote:
>
> Yes and no.  Fat and ketones are not the same thing.  Fat is  
> composed of fatty acids, and are burned as such.  When the fatty  
> acids are bound together with a molecule of glycerol, it's called  
> triglyceride, and most stored fat is in that form.  Fat circulating  
> in the blood is in the form of both free fatty acids and  
> trigylceride.  Ketones are molecules produced in the liver, from  
> fatty acid molecules, but the liver only does this when stored  
> glycogen is very low.  Some, but not all, of the cells that burn  
> glucose can also use ketones.
>
> This is correct.  Carbohydrate isn't really "produced" from fat,  
> but the glycerol molecule that binds three fatty acid molecules  
> into a triglyceride can be converted into glucose, so in a sense a  
> small amount of glucose can be culled from the fat you eat, most of  
> which is in the form of triglyceride.


Thanks for the explanations Todd.  You seem to know a lot about this-  
is it your job?

 From your description above, it sounds like when glycogen runs low,  
the body breaks down fats to produce fatty acids to power most cells,  
ketones to power some of the glucose-burning cells, and the glycerol  
produced in the process powers the rest.  Am I on the right lines?

What I don't see is the need for glucogenesis, if glucose can be  
produced from fat.  Is this just a way to get some useful calories  
from excess protein?



> <snip>
>
> Your cells will not make much use of ketones until no more glucose  
> is available (some ketones are used all the time, but not a lot).   
> Your *hepatic* glycogen reserves function as a reservoir of  
> glucose, from which your tissues can draw, so that your  
> availability of glucose doesn't depend on what you ate a few hours  
> ago.  This is necessary because your blood glucose needs to be kept  
> within narrow bounds.  So as soon as you eat any quantity of  
> carbohydrate, the first thing that happens is it's dumped directly  
> into the blood as glucose (and other simple sugars).  If glycogen  
> storage is not full, it gets topped up.  If muscle glycogen is not  
> full, it gets topped up.  Any cells that can use glucose will  
> attempt to do so.  If BG still needs to be lowered, the rest will  
> be pulled out of circulation, converted to triglyceride and stored  
> that way.
>
> After a couple of days you should be in ketosis.  When you start  
> producing ketones, you produce various kinds.  Not all of them can  
> be used as fuel; in fact one sort is toxic and must be dumped.  I  
> believe that's acetaldehyde, but I could be wrong.  This is from  
> memory.  So your body will excrete the ketones it doesn't or can't  
> use.  They will be present in urine, sweat, and breath, since your  
> breath contains water droplets.  If in your breath or sweat, there  
> will be that distinctive "ketoney" odor.  But if you are drinking a  
> lot of water and peeing a lot, most of the ketones will exit that  
> way, so there might not be many going out through your breath--not  
> enough to cause the taste and odor.
> A couple of days would probably only just induce a mild ketosis  
> anyway.

This makes it sound like ketosis is a bad state.  If ketosis does not  
begin until glycogen is depleted, doesn't that leave you with no  
flight or flight reserves?  What happens, for example, to people who  
have no access to carbohydrates for extended periods of time (ie  
several months)?  Wouldn't they be incapable of anaerobic exercise?   
(I can't believe that.)  Or is there a difference between hepatic and  
muscular glycogen (or the body's use of it anyway).


Since you seem pretty well up on this, can you recommend any books on  
the subject?  I keep feeling I should get some more technical  
knowledge about biology and biochemistry because I want to go into  
alternative health care in the future, so I will need to know my stuff.


Cheers

Ashley