Kenny Brown wrote:

>You are correct fat can not be directly converted to
>glucose, however, it is indirectly coverted to
>glucose. ...
Its converted to usable and burnable energy, but hardly into glucose.
(except for the glycerol part, see below).

>The break down of fat is known as lipolysis.  Only the
>triglycerides are the major souce of energy. ....
This (fat) energy is *the*   major souce of energy.
In the average human.

>...
>The whole process is termed Gluconeogenesis and is the
>process by which fat and protien are broken down and
>used for energy
Gluconeogenesis is the term for creating glucose new
from non-carbohydrate sources.
This is from protein, and to a very smal extent from
the glycerol in fats (see below).

>Stricly speaking Fat is not turned into glucose, this
>would require the glucose to go through the Krebs
>cycle.  This does not happen. ...
Yes.

From Wade:
>> Stricly speaking, a trygliceride is made up of three
>> fatty acids attached to a
>> glycerol 'backbone'.   Isnt the glycerol converted
>> to glucose?
Triglyceride contain of one glycerol molecule (relative small)
with 3 Fatty-acid chains attached to (relatively much bigger).
Only the small glycerol part is turned into glucose, what means
that *very* much more energy will come from the long fatty acids.
For a diet totally absent of carbohydrate this small part may
- as Wade pointed out- indeed become important.
Because (the rest of) fat is burned directly but the body does
actually essentially needs some glucose.
Even from much fat , the glucose yield will be very small
and still the most of the actually needed glucose will be
synthesised by gluconeogenesis from protein.

Todd:
>>> The critic is correct, and Neanderthin is
>>> wrong.  You can't turn
>>>fats into glucose

I think it's not a real drawback for Neanderthin IMO.

What does this all mean for nutrition, anyway?
1. The muscle fibers that burn fatty acids (or ketones) are
   different from the ones burning glucose.
 ! To change from carbs to fats will take some conversion time.
   And they are more endurance-type muscles.
   Highest pwer muscles need to burn glucose.
 ! Therefore fats won't be best for high performance sports.
2. There are tissues with a mandatory need for glucose,
   namely brain and blood cells.
   Their needs (this are about 500-700 kcal/day w/o ketosis)
   had to be eaten directly as (paleo-)carbohydrates or otherwise
   much additional protein will be needed for gluconeogenesis.
 ! This additional protein will be taken from the body or must be eaten.
 ! As the process puts considerable strain on the kindeys
   it is a drawback of ketogenic diets.

What i find interesting is that (1) tells that *most*
tissues live on fats anyway, in *normal* diets.
Though normal diets are very high in carbohydrates.
I think this comes from missing vitamins and enzymes (namely thiamin)
which hinderes the body from burning the carbohydrates in the krebs
cycle. Fats have a own pathway besides krebs cycle, right Kenny?

regards
Amadeus S.

(1): http://medtstgo.ucdavis.edu/endo/lecture/metGlucose.htm
     (the very first sentences)

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