Brian brings out some excellent points which we have discussed in previous
posts over the last year or two. At the risk of repeating myself, let me
briefly address some of his comments.
1. "The available information on Paleolithic peoples is so scanty that
it seems specious to believe that one can follow their nutritional practices
with more than a modicum of accuracy".
I dont think few scientists studying paleodiets would argue this
point. However there are some obvious deductions which allow basic
generalizations which have enormous impact upon present day health (i.e.
dairy products could not have been a component of stone age diets). Similar
arguments can be made for salt (sodium chloride), trans-fatty acids (except
for trans vaccenic acid - trans 11, 18:1), cereal grains, refined
carbohydrates, fatty meats and other "modern" foods.
2. "The picture we have of contemporary hunter-gatherers suggests that
few conclusions can be drawn due to the high variability of nutritional
patterns across different populations, in addition to the difficulty of the
contaminating influences of contact with industrial and post-industrial
cultures."
There is little doubt that studies of contemporary hunter-gatherers,
particularly those done in the past 30 years or so are influenced by the
relative degree of contact these peoples have had with industrialized
societies. Many of these contaminating influences of civilization upon
dietary practices have been noted and qualified, particularly in the more
recent (in this century) studies of hunter-gatherers (eg. carbohydrate in
the diet of the Inuit (1-4)). The information that has been garnered by
ethnologists and anthropologists has value and provides insight into what
the components of the completely aboriginal diet would have been prior to
contact and acculturation. We have comprehensive and detailed lists of wild
plants and animals that were consumed by hunter-gatherers all over the
world. These lists have been compiled in the recent past in partially
accultured peoples, as well as in the 18th and 19th century in completely
unacculturated hunter gatherers. The qualitative substance of what these
people ate is not so much in question as is the quantitative issue. Data
from our research group indicates that the range of diet in terms of
plant:animal (P:A) subsistence ratios (and hence macronutrient variation)
was large (0-5%P:95-100%A to 76-85%P:15-24%A), however the variation was
surprisingly narrow relative to the central tendency. In all world wide
hunter gatherers (n=229) listed in Murdock's Ethnographic Atlas, the median
and modal values for animal food subsistence is 56-65% whereas the median
and modal value for plant food subsistence is 26-35%. If the data is
expressed as ratio level data, then the mean value for animal food
subsistence with its SD is 6.77 + 1.85. The mean value 6.77 would fall
within the 66-75% animal subsistence level. The meaning of this
ethnographic data is clear. In virtually all world wide hunter gatherer
populations (whereever it was ecologically possible), animal food would have
always comprised more than half of the dietary intake. Therefore, the
variability in diet among worldwide hunter gatherers is not as
quantitatively variable (in terms of macronutrients) as has previously been
assumed. Not a single world wide hunter gatherer society derives its entire
subsistence solely from plant foods, and only 10% of the total (n=229)
studied, derive 56% to 85% of their food calories from plant food.
3. The third issue brought up by Brian is the issue of longevity. I
think that most gerontologists are in agreement (at least in terms of animal
experiments) that caloric restriction extends lifespan. Whether or not this
general principal applies to humans is not known. However, in humans, it
appears that there is a strong genetic component which is independent of
environmental factors (5). The reported longevity of Hunzas and Vilcambas
may have a genetic basis or it may be a function of diet or a combination of
both. Although Brian suggests that " No other nutritional variables appear
to be reliably associated with longevity", this clearly is not the case.
Apparently Brian is unfamiliar with Harman's classic free radical theory
reviewed in (6) and generally accepted as a contributor to the ageing
process by most nutritionists and gerontologists (7-9). Because the hunter
gatherer diet contained few or no cereal grains and high levels of fruits
and vegetables (compared to modern standards), the antioxidant intake from
phytochemicals and vitamins would have been quite high. In analyzing
hunter-gatherer subsistence ratios using modern foods, computerized dietary
analyses by our research group has shown that a diet composed of lean meats
(55% total energy) and fruits and vegetables (45% energy) yields much higher
antioxidant levels than for grain and dairy based diets.
4. "With regard to pathology, a high intake of red meat has been
associated quite consistently with the development of cancers (6)."
There is no doubt that multiple epidemiological studies have shown
an association between high consumption of red meat intake and many types of
cancers. However, there is just as strong epidemiological evidence to show
a relationship between saturated fat intake and cancers (checkout medline,
there are thousands of references). Because, modern commercially available
red meat contain enormous amounts of saturated fat (a t-bone steak with 10%
fat by weight contains 50% fat by energy), it is quite difficult if not
impossible for epidemiological studies to untangle the effects of the meat
protein with the meat fat. There is very little experimental evidence to
show that protein is a mutagen whereas there numerous animal studies and in
vitro cell studies indicate that high fat diets can serve as promoters of
many diverse cancers. The fat content of muscle meat in wild game animals
ranges
from 1-2% by weight or about 10-20% by energy. Thus, the muscle of game
meat (the staple food of hunter-gatherers) is almost entirely protein.
5. "Perhaps the Paleolithic diet (if there is such a thing?), in the
form of a relatively high fat and protein intake by today's standards"
Reconstructed "paleolithic diets" by my colleague Boyd Eaton (10),
as well as estimates that we will soon publish, do not indicate that such
diets were high in fat. During certain times of the year, these types of
diets, particularly in northern latitude hunter gatherers, may have equaled
or exceeded the fat content of modern diets, however the aggregate data
suggests that the total fat content was either equal to or lower than that
in modern diets. An important distinction here is the type of fats that
were consumed. As we have previously shown, the fatty acid composition of
pre-agricultural diets would have been much different than the modern diet
(11).
6. "Perhaps the Paleolithic diet (if there is such a thing?), in the
form of a relatively high fat and protein intake by today's standards, was
evolutionarily selected because it was the most effective to develop the
human form for the first two decades of life with the goal of effective
reproduction."
Evolutionary theory certainly agrees with this concept, at least in
context. The diet that humans evolved with is the diet which we are
genetically adapted to, and the diet that tends to optimize reproductive
potential. Most nutritionists would agree that diets high in fruits and
vegetables such as the "paleodiet" would be healthful not only during the
reproductive years, but also during the post-reproductive years. Similarly,
the low fat content and fat balance (high N3, high monounsaturates, low
trans fat, low saturated fat) of stone age diets would also promote health
in the post-reproductive years. If a high protein intake is countered by a
high fruit and vegetable intake, the potential deleterious influence high
protein intake upon acid/base balance and hence calcium metabolism can be
overcome. Indeed the potential renal acid load (PRAL) of a diet in which
45% of the caloric intake is composed of fruits and vegetables will result
in a net alkaline load (12). I also suspect that a salt restricted diet
(such as the paleodiet) would also be just as beneficial for older people,
if not more so, than for those in their prime reproductive years.
7. "One wonders if instead of chasing the chimera of 'Paleolithic man',
we should not be looking more carefully at the evidence from the 20th
century".
Indeed!, What was it that Santayana said? Something like: those who
are unfamiliar with the past are condemned to repeat it? (Dean - help me out
on this quote - you are the quote master). By ignoring the genetic and
evolutionary basis for our present day dietary requirements, we are
essentially throwing out eons of evolutionary experience - experience that
is still far wiser than the mind of 20th century man and his fledgling
science.
Cordially,
Loren Cordain, Ph.D., Professor
Department of Exercise and Sport Science
Colorado State University
Fort Collins, CO 80523
tel: (970) 491-7436
fax:(970) 491-0445
email:[log in to unmask]
http://www.colostate.edu/Colleges/CAHS/ess/cordain.htm
REFERENCES
1. Bang HO, Dyerber J. Lipid metabolism and ischemic heart disease in
Greenland eskimos. Adv Nutr Res 1980;3:1-22.
2. Sinclair HM. The diet of canadian indians and eskimos. Symposium
Proc 1953;12:69-82.
3. Heinbecker P. Studies of the metabolism of eskimos. J Biol Chem
1928;80:461-75.
4. Krogh A, Krogh M. A study fo the diet and metabolism of eskimos
undertaken in 1908 on an expedition to Greenland. Meddelelser om Gronland
1913:51:1-52.
5. Mueller LD, Rose MR. Evolutionary theory predicts late-life
mortality plateaus.Proc Natl Acad Sci 1996;93:15249-53.
6. Harman D. The aging process. Proc Natl Acad Sci 1981;78:7124-28.
7. Cutler RG. Antioxidants and aging. Am J Clin Nutr 1991;53:373s-9s.
8. Ames BN et al. Oxidantss are a major contributor to aging. Ann NY
Acad Sci 1992 ;663:85-96
9. Sohal RS. Relationships between antioxidants, prooxidants and the
aging process. Ann NY Acad Sci 1992 ;663:74-84
10. Eaton, S.B ., Shostak, M., et al. The Paleolithic
Prescription: A Program of Diet & Exercise and a Design for Living: New
York: Harper & Row, 1988.
11. Eaton SB, Eaton SB 3rd, Sinclair AJ, Cordain L, Mann NJ. Dietary
intake of long-chain polyunsaturated fatty acids during the
paleolithic.World Rev Nutr Diet 1998;83:12-23.
12. Remer T, Manz F. Potential renal acid load of foods and
its influence on urine pH. J Am Diet Assoc 1995 ;95:791-7 .
Loren Cordain, Ph.D., Professor
Department of Exercise and Sport Science
Colorado State University
Fort Collins, CO 80523
tel: (970) 491-7436
fax:(970) 491-0445
email:[log in to unmask]
http://www.colostate.edu/Colleges/CAHS/ess/cordain.htm
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