> Why eat additional fat if you have body fat you'd want to use?

To increase caloric intake without increasing insulin.  With satisfactory
caloric intake, one feels less hungry and uses more body stores of fat for
energy.

From Mastering the Zone (Sears, 1997):

"If you have eaten a hormonally correct meal, you won't be hungry for the
next four to six hours because you will be maintaining blood sugar levels.
For the same biochemical reason, you will have a very sharp mental focus
and you will be simultaneously tapping into your stored body fat as a
virtually
unlimited calorie source.

Great, but what happens when the "carburetor" is out of tune?  The first
warning sign is that you get hungry before the end of that four- to
six-hour time period.  But symptoms alone will not tell you if you have
produced too
much insulin or not enough insulin with your last meal, because in either
case you will get hungry within two to three hours after the meal.  Why is
that?

Well, if you are producing too *much* insulin, then blood sugar levels will
be driven down, and your mental alertness drops.  In other words, you get a
loopy feeling.

However, if your insulin levels are too *low*, then there is not enough
insulin crossing the blood brain barrier to interact with the hypothalamus
to prevent the synthesis of neuropeptide Y, probably the most potent
stimulator of appetite.  And here is the irony.  Although the brain is
getting more than adequate amounts of blood-sugar and thus retaining
excellent mental acuity, you have a growing hunger due to the increase in
neuropeptide Y levels in the brain.

So now you can play food detective to retune your carburetor.  If you eat a
meal and feel hungry and loopy within two to three hours (if not sooner),
then that meal contained too many carbohydrates relative to the amount of
protein.   Correspondingly, if you are hungry within two to three hours,
but maintain good mental acuity, you have pushed insulin levels too low.
The
next time you eat that same meal, increase the amount of carbohydrate
blocks by one."

Rob