Ashley Moran wrote:

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

Nope, and for that reason you should question everything I say.  This is 
just one of my...hobbies, I guess you could say.  As a 52 year-old who 
struggled with weight problems for decades (and I'm still not what you'd 
call lean), I got interested in all this in a big way some years ago 
when I read Barry Sears' books, and then did wider reading on 
carbohydrate reduction, and eventually paleo nutrition.

> 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?

Yup, that sounds right.  Of course, even when glucose isn't low, there 
is normally some fat-burning going on all the time.  Many cells can and 
do use both glucose and fat for fuel.  But yes, when you stop eating 
carbohydrate, first you'll draw on your glycogen reserves (glycogen is 
actually a starch, but it's converted back to glucose, like other 
starches), and since you're not eating carb to replenish them, they'll 
run out (near enough.  I think the liver doesn't allow them to empty out 
completely but keeps a small emergency supply).  At that point, those 
cells that can burn fatty acids will do so, and the liver will increase 
its production of ketones from fat as well, and those tissues that can 
use ketones instead of glucose will do so.  In short, your metabolism 
goes into glucose-sparing mode.  At the same time, your liver also 
initiates gluconeogenesis to provide some glucose from protein.  The 
production of ketones from fat uses energy, so some of the calories in 
the fat are actually "wasted" by the liver in making the ketones, which 
means that the liver's metabolic rate goes up, in effect.

> 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?


The amount of glucose that is recovered from triglyceride is very small, 
not enough to supply glucose to the cells that need it, such as red 
blood cells.  So glucogenesis is needed to provide whatever glucose is 
needed over and above the small amount recovered from triglyceride 
(assuming none is eaten).

> 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).


People who start out on ketogenic diets may well find that they have no 
fight or flight reserves for a while.  They may feel sluggish for a week 
or so.  But as more tissues that can burn fat do so, as those that can 
burn ketones do so,  the actual demand for glucose goes down.  It 
doesn't happen overnight.  These people will also become more efficient 
at gluconeogenesis, so their glycogen reserves will be gradually 
replenished.  In short, they achieve a different metabolic equilibrium.

People who consume a lot of carbs are constantly putting their bodies in 
a state where all that incoming glucose must be dealt with.  So every 
cell that is capable of using glucose for fuel does so, and fat-burning 
metabolic pathways are downregulated.  Since insulin is the hormone for 
putting away sugar--either into glycogen storage, or into cells for 
burning, or into fat stores--it is constantly "working" in a high-carb 
environment.  And the result is often insulin resistance, a kind of 
overuse syndrome.

> 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.

This web site, though technical, does a good job of laying out the 
basics in one place: http://www.zonehome.com/met/met.htm

Todd Moody
[log in to unmask]