I've enjoyed the spirited debate that we have carried on over the past 6
months. The extensive post by Mary and Sally on January 25, 1998 was a
rebuttal to my lengthy post of October 9, 1997 which in turn was a
response to Mary and Sally's post of June 29, 1997. Interested
readers may access this on-going debate by viewing the Archives of this
list serve(http://maelstrom.stjohns.edu/archives/paleodiet.html).
Except for a few points which I will address, I feel that my viewpoint
and perspective in regard to Dr. Enig's and Sally Fallon's
interpretation of paleodiets has been adequately expressed in my post of
October 9th. We clearly differ on a number of issues but also seem to
be in agreement on others.
A few brief responses to Mary and Sally's post are in order.
1. I agree to disagree with Mary and Sally on the role of dietary
saturated fat and coronary heart disease.
2. The total fat content of elk muscle ranges from 1.5-2.0 % by
weight or between 12-16% by calories. Thus a 100 gm (~1/4 lb) sample
would contain 1.5 gms total fat and about 0.5 gm saturated fat. Most
wild herbivore muscle contains a similarly low fat content. In
contrast, a 100 gm lean sirloin beef steak (USDA data) would contain
7.2% total fat by weight and 35% fat by calories with 2.8 gms of
saturated fat. Thus, a lean beefsteak contain 560% more saturated fat
than does a comparable 100gm elk steak. This increase in fat content
of domesticated animals is a result of selective breeding and feedlot
provisioning which induces intramuscular lipid storage that is not found
in wild animals.
My contention is that it would have been extremely difficult or
impossible for pre-agricultural man to have had a regular source of
dietary saturated fat. Since dairy fats (cream, butter, cheese) were
not part of man's diet until about 5-6,000 yrs ago and since wild
animals regularly consumed by pre-agricultural man have extremely low
levels of saturated fat, there would not have been an unlimited source
for the atherogenic fats (12:0,14:0, 16:0) as there is today with dairy
products and fatty meats. One of the few ways in which
pre-agricultural man could have obtained regular high levels of dietary
saturated fat would have been by selective butchering in which fatty
portions of the carcass were consumed to the exclusion of the rest of
the carcass. This is assuming that the animal even had fatty storage
depots - most wild animals have seasonal variations in body fat, and
only in late summer and early winter are moderate (~3-5% total body
weight) fat stores present. Peri-nephral, marrow and subcutaneous fat
stores, are not present in most northern latitude large herbivores for
many months of the year.
From an energetic perspective (i.e. optimal foraging theory
(1)), it is functionally inefficient to kill large animals and consume
only the the fatty portions of the animal. Clearly, the maximal amount
of lean flesh that could have been consumed, would have been consumed.
Despite this, much of the lean carcass would have been unavailable for
consumption, particularly when carbohydrate food (plants) was limited
because of the ceiling or limit to the amount of protein which humans
can consume. As I have pointed out in many previous postings, there is
an upper limit to human dietary protein intake which is roughly 50% of
total calories or about 300 gm (2). Thus, without either a source of
added carbohydrate or fat, much of the potential energy from the lean
muscle of wild animals is unavailable for consumption. Optimal foraging
theory would predict that pre-agricultural man would have always eaten
close to this upper limit for protein, especially when large herbivorous
animals formed the bulk of the dietary intake. This macronutrient
intake pattern (40-50% protein, 15-25% fat; 25-35% carbohydrate)
represents the dietary pattern for which pre-agricultural humans are
adapted and which provides optimal health in this group. High intake
of animal based diets (65% total calories or more) are not atherogenic
in this context because of the hypocholesterolemic effect of the
enormous protein intake (3,4), the relatively low saturated fat intake
and the relatively high intake of monounsaturated fats, and long chain
polyunsaturates (20 carbon or >) of both the n6 and n3 varieties. The
low levels of carbohydrate (pre-agricultural humans did not consume
grains) in paleodiets served to further prevent coronary heart disease
by reducing triglycerides and VLDL cholesterol while elevating HDL
cholesterol.
3. I agree that that carbohydrate mixed with fat generally results
in a lower glycemic (blood glucose) response. My point here was that
the insulin response to fat + carbohydrate is greater than to
carbohydrate alone because of the stimulatory effect of fat ingestion
upon glucose-dependent insulino-tropic polypeptide (GIP) (5).
4. I suggest that Mary and Sally carefully read some of the
previous references I have provided in my Oct 9 posting. Mann et al.
(6) have clearly shown in coronary artery biopsies performed post
mortem on Masai warriors the evidence for extensive atherosclerosis on a
high saturated fat diet of mik and blood. This article even shows an
example photograph of atherosclerotic lesions in coronary artery cross
sections.
5. It is sheer folly to deny the calciuretic effects of sodium.
This effect has been known for more than 40 years and the evidence in
humans is unequivocal (7). In the paper (8) that Mary and Sally cite
to support their contention that sodium is not calciuretic, the reason
that sodium did not cause a calciuretic effect is because
an acute load was given rather than a chronic load. The authors of the
article even acknowledge this by saying, "Results from study 1 suggest
that the use of acute load tests for studying the effect of sodium
chloride on urinary calcium excretion is inappropriate. Because
urinary sodium excretion did not change significantly from fasting
concentrations, it appeared that dietary sodium was retained for the 3h
that urinary excretions was monitored and it is possible that the
expected changes in urinary calcium were prolonged past the collection
period of the acute load test".
The type of foods (milk, cheese, butter, cream, salt, fatty meats, whole
grains etc) which Mary and Sally recommend as healthful are all foods
which are recent additions to the human dietary experience and which
were only incorporated as staple foods in the past 10,000 years as
humans made the transition from hunter-gather to farmer. High dietary
intakes of sodium, saturated fat, dairy foods and cereal grains are
inconsistent with human evolutionary experience. It is this
discordance between our genetically determined nutritional needs and the
recent foods ushered in by the "agricultural revolution" which
invariably cause nutritionally related health problems.
Cordially,
Loren Cordain, Ph.D.
Professor, ESS Dept
Colorado State University
Fort Collins, CO 80523
REFERENCES
1. Hawkes K, Hill K, O'Connell JF. Why hunters gather: optimal
foraging and the Ache of eastern Paraguay. Am Ethnologist
1982;9:379-98.
2. Speth JD. Early hominid hunting and scavenging: the role of
meat as an energy source. J Hum Evolution 1989;18:329-43.
3. Wolfe BM. Potential role of raising dietary protein for
reducing risk of atherosclerosis. Can J Cardiol 1995; 11 (suppl
G):127G-131G.
4. Wolfe BM et al. Short term effects of substituting protein for
carbohydrate in the diets of moderately hypercholesterolemic human
subjects. Metabolism 1991;40:338-43.
5. Collier GR et al. The acute effect of fat on insulin secretion.
J Clin Endocrionol 1988;66:323-26.
6. Mann GV et al. Atherosclerosis in the Masai. Am J Epidemiology
1972;95:26-37.
7. Nordin BEC et al. The nature and significance of the
relationship between urinary sodium and urinary calcium in women. J Nutr
1993;123:1615-22.
8. Whiting et al. Calciuretic effects of protein and potassium
bicarbonate but not of sodium chloride or phosphate can be detected
acutely in adult women and men. Am J Clin Nutr 1997;65:1465-72.
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