The "narrow" view of a paleodiet would be to say that we literally should
not eat anything our paleolithic ancestors did not have available to them.

Unfortunately this narrow view is also completely and totally impossible to
live up to.  We don't know for certain exactly what they ate, and it is a
virtual certainty that some of what they ate is not available to us anymore
and will never be again.

Furthermore, you have the question of WHICH paleolithic ancestors.  Humans
have been all over the planet for a very, very long time.  So which humans
do you want to emulate, the hunter/gatherers of Australia from 90,000 years
ago, or the hunter/gatherers from Africa 90,000 years ago, or the
hunter/gatherers from Europe 90,000 years ago?  And before you jump to the
conclusion that because you may be of European extraction, the European
hunter/gatherers would be the obvious choice, think again, because Asian
and African blood got mixed into the European gene pool over and over and
over again in the last 10,000 years.  Not to mention that Greece and France
are both part of "Europe" and are really awfully different from each other.

The simple fact is that we all--every one of us--has a mixed genetic
inheritance from different groups.  Not even the insular Chinese ever had a
completely "pure" gene pool.

It seems to me very clear that humans evolved to eat a very wide variety of
foods, and as we also adapted to be wanderers, our systems are probably
able to handle a good range of different foods.  Trying to limit your
intake to what some ancestor of yours 25,000 years ago ate is impossible
because you don't know exactly what that ancestor ate, and anyway what that
one ancestor ate may have been radically different from what another
ancestor from the same time period ate, and you can't know for sure what
either of them ate anyway, and even if you did you probably couldn't
duplicate it because some of it would be extinct anyway.  ;-)

Some things we can say for absolute certain regarding how humans evolved to
eat, however:

1) Humans evolved eating meat.  There is no support, period, for
vegetarianism as a natural human diet.
2) Humans did not evolve eating either cereal grains or the dairy products
of other animals.
  2A) Dairy products contain lactose, which most of the world population
cannot process, and casein, an unusual protein quite unlike any that any
hunter/gatherers would ever encounter, and foreign proteins may elicit
immunological responses which aren't desirable.
  2B) Cereal grains contain glutens, large and unusual proteins also
completely unlike anything any hunter/gatherer would encounter normally,
and which may also have the same potential sequelae of undesirable
immunological responses.
3) A study of modern hunter/gatherers shows a propensity to eat far more
protein from nuts and meats than is supposedly "ideal" today.
4) A study of modern hunter/gatherers also shows clearly that for the most
part, high carbohydrate intake is a little unusual, and that most
carbohydrates eaten most of the time by pre-agricultural peoples is low on
the glycemic index (slow to digest).
5) Fruit intake is usually limited and the fruits eaten less sweet, less
colorful, and more fibrous than most modern fruits.

A case can be made that the pigments in modern fruits cause a problem; I'm
aware of at least one researcher who holds that theory and is doing some
study on it.  Nevertheless from all of this it seems that we can make some
pretty good guesses on what is a fairly natural, healthy diet:

No grains or grain products.  No dairy or dairy products.  Limited intake
of modern fruits, with concentration on things that are still close to
their natural state, i.e. blueberries, raspberries, etc.  Plenty of meat,
plenty of nuts, plenty of protein.  Lots of fibre.

The good rule of thumb in any of this is clearly just to look for anything
you can eat raw or nearly-raw and that's probably an okay food.  If you
want to get really anal and argue that pineapples wouldn't have been
available to your ancestors, well, maybe you can build a case for it, but
it strikes me that if you're lmiting your intake of these foods as treats,
you probably don't have much to worry about even if they ARE a problem for
you (which they might well not be, since they DON'T contain foreign
proteins.)

It strikes me that trying to find the ideal human diet is a search for the
golden fleece.  The question is what are logical, sensible principles that
aren't too ridiculously difficult to live with.

 -=-=-

Once in a while you get shown the light/
 In the strangest of places if you look at it right   ---Robert Hunter

http://www.syndicomm.com/esmay