Having recently read Cordain's book, I suspected there would be
discussion of it here, so I resubscribed.  So first, Merry Christmas
and Happy New Year to everybody.

Anyway, I checked out the archives and the discussion, and I have to
say that I find myself in full agreement with Don Matesz's remarks.  I
think the Cordain approach to paleo is a useful option for those who do
not do so well on the Neanderthin approach.

In terms of carb intake, Cordain's high end is about 40% of energy, the
same as the Zone.  At the low end, he has 20%, I believe.  In relation
to an "average" 2,000 kcal diet, this means between 100g and 200g per
day.  Personally, however, I am not so keen on the "ratio" approach.
According to Walsh (http://www.zonehome.com/met/met.htm), we use about
180g of glucose per day, mostly by the brain and red blood cells.  That
would vary somewhat by body weight, because of differences in blood
volume, but not all that much.  Utilization of glucose by the brain
should not vary much either.  So I take this to be a ceiling value:
anything more than 180g/day is converted to SFA anyway.

At the low end, it's harder to say.  The brain and red blood cells need
some glucose, but the brain (not the red blood cells) can replace some
glucose with ketones, so that the total glucose demand may drop to as
low as 40% of what it is when carbs are plentiful.  Using that as for
estimating, that would mean that we can "get away with" as little as
72g/day, without having to resort to much gluconeogenesis.
Gluconeogenesis is not problematic in itself, but it does increase
one's protein requirement substantially.  This is because the amino
acids are only converted to glucose with 58% efficiency.  Also the
glucocorticoids (e.g., cortisol) that are used to stimulate
gluconeogenesis, the so-called "stress hormones", may not be the best
thing to have turned on all the time.

Anyway, if all this is correct, it follows that the carb "window" in
which one avoids both gluconeogenesis and conversion of glucose to fat
is between 72g and 180g per day.  This is actually not far from what
Cordain recommends, based on field studies of hunter-gatherers.

Cordain is opposed to the liberal consumption of dietary saturated fat.
 In part it's because he accepts the "diet-heart" hypothesis, that SFA
contributes to heart disease by elevating LDL cholesterol.  In some
people (such as me) it certainly does elevate LDL cholesterol, but the
significance of that is still in dispute.  The Eades argue that it is
only small-dense LDL that is dangerous.  They may be right.  The other
point, which Amadeus and I argued many times here, is whether SFA
contributes to insulin resistance.  I admit that there is some evidence
that it does (see
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8596494&dopt=Abstract,
for example.  I think Sears has other references on this), although I
still find the whole thing confusing and the evidence equivocal.

But here's something interesting: Imagine a 2,000 kcal diet, an
"Ornish" sort of diet.  Imagine that it contains about 60g of protein
(= 240 kcal); about 22g of fat, most of which is not saturated (= 200
kcal, or only 10% of calories).  The remaining 1,560 kcal are from
complex carbs, about 390g.  Since the body can only use about 180g of
those carbs in a day, the remaining 210g will be converted to fat,
virtually all of it saturated.  Assuming some loss of energy in the
conversion, that comes to at least 80g of saturated fat in circulation,
from this extreme "low-fat" diet.

Now consider a 2,000 kcal "Atkins" diet.  This time we'll set the carb
intake at 20g (=80 kcal) -- very low.  We'll assume a more generous
intake of protein, from meat; say, 120g (=480 kcal, but actually less,
because of the inefficiency of the conversion).  The remaining 1,440
kcal must come from animal fat.  That means 160g of animal fat.  Animal
fat is about 50% saturated (a bit less, actually, but let's keep it
simple), so that comes to about 80g of SFA.  The rest is mostly
monounsaturated.

So, you see, the Ornish plan and the Atkins plan are about equal in
terms of how much SFA they put into circulation.  So if the idea is to
minimize SFA in order to reduce insulin resistance, the thing to do is
to favor the leanest meats and get monounsaturated fats and EFAs from
nuts, etc., rather than from animal fat, as much as possible.  And keep
carbs below 180g/day.  That's pretty close to what Cordain recommends.
Furthermore, if you're losing weight you are utilizing stored fat from
adipose tissue, much of which is saturated anyway.  So if you take two
people on identical diets, one of whom is losing weight (the other is
maintaining), the person losing weight will be putting more SFA into
circulation.

So, I think Cordain's approach makes metabolic sense for many of us.