I posted a version of this last night, but it didn't show up.
Apologies if you get two copies!


At 15:33 +1000 5/2/03, Phosphor wrote:

 >Richard, I'm suspecting this may be another Tall Tale.  however it requires
 >a good looking at. but do you want to hedge your bets now, or follow the
 >white line to death or glory?

Unlike you, I don't see discussions on this list as leading inexorably
to either death or glory. I'm here to learn things and occasionally to
share what I already know.

If presenting a hypothesis which turns out to have major flaws is what
it takes to learn more about the concept, I'm more than happy with
that. In fact, you often learn more when you start with a false theory
than when you guess right first time.

So, what's your background in physiology? Can you decipher the
discussion of the nitrogen cycle in that link I sent in my last message?


 >here's a sample...
 >
 >And his definition of "rabbit starvation" is a far cry from what Stefansson
 >described among the Northern Canadian Indians and Inuit back in his book The
 >Fat of the Land. Cordain, politically correct as ever, claims that the
 >sickness and wasting that occurs when large amounts of lean animal protein
 >are eaten occurs because the body has hit a "protein ceiling." REAL rabbit
 >starvation, however, as defined by Stefansson happened when Inuit and/or
 >Indians would not get enough animal fat to go along with their catches of
 >lean meat, which were not preferred by these peoples.
 >http://www.thincs.org/discuss.cavemen.htm [scroll down to stephen byrnes].

Both of those statements say the same thing. The "protein ceiling" is
due to the liver being unable to metabolise any more ammonia. The
"rabbit starvation" is due to hitting the protein ceiling. I think
you'll find that Stefansson also pointed out that the indians were
just as happy to consume carbs with protein as fat. This is interesting,
because carbs are most readily available when fat is at its scarcest.

The difference between the statements pivots on the fact that
Stefansson was reporting on tribal wisdom (eat too much protein,
get sick). Whereas Cordain worked out *why* they get sick.

I found this web page:
http://www.wi.ca/imcal/comments/index1146.htm

Which contains an apparent quote from Cordain on the issue of the
protein ceiling. Note that this is now fourth-hand information
(Cordain to Joe to KP to to me to you):

Here is a quote from Dr Cordain that Joe gave to me on this subject. "I
know of no health problems associated with high (250-300 grams/day)
protein intakes that you describe. In fact, to the contrary. High
protein lowers total blood cholesterol, increases HDL, reduces
triglycerides, improves insulin metabolism, facilitates weight loss in
the obese by blunting the appetite and increasing resting metabolism.
Further high protein intakes have been shown in epidemiological studies
to reduce the risk of high blood pressure, coronary heart disease, bone
mineral loss as well as lengthening survival for women with breast
cancer. As long as sufficient fruit and vegetable intake (35% energy)
accompanies high protein intake, there is no increased risk for
osteoporosis or bone mineral loss. Finally, a recent clinical trial has
shown that high protein diets (25-30% energy) have no adverse effects
upon kidney function. There is no absolute ceiling such as 300 grams
for all persons. The physiological protein ceiling is based upon body
weight and also varies from person to person with the same body weight.
The physiological protein ceiling is primarily determined by the
ability of the liver to get rid of (metabolize) the dietary nitrogen (a
toxic compound) that is a by-product of protein metabolism. Nitrogen is
eliminated from the body by first converting it to urea in the liver
and then excreting it in the urine and feces. In order to convert
nitrogen to urea in the liver, a number of enzymes must be up-regulated
(built) for this conversion. The rate limiting (controlling) enzyme for
the conversion of nitrogen to urea is argininosuccinate synthetase.
This enzyme cannot be infinitely up-regulated in the face of increasing
dietary protein intake. Isotopic tracer studies in humans show that the
mean rate of maximal urea synthesis is 65 mg nitrogen per hour per kg
body weight to the 0.75 power and the range is (55-75). If the dietary
protein intake exceeds the ability to convert nitrogen to urea, then
excess nitrogen spills into the blood stream as ammonia and amino acids
which sets up a series of metabolic events that leads to nausea,
diarrhea, electrolyte imbalance and ultimately death if high protein
intakes continue for weeks and months. We have calculated the mean
maximal protein intake for an 80 kg subject consuming 3000 kcal to be
250 g/day (range: 212-292 g/day)." (80 kg is about 175lbs)

  ...R.