My contributions to the listserve have been minimal in the past couple
of weeks because of the arrival of our third son two weeks ago and
because of a concerted effort to complete my cereal grain manuscript,
which is now complete & hopefully should appear in a forth coming issue
of the World Review of Nutrition and Dietetics.
In regards to the out of Africa hypothesis and its relationship
to diet, I think the data supports the concept that early humans left
Africa by at least 1 MYA or possibly earlier and were replaced by
anatomically and behaviorally modern humans in the past 40-60,000 years.
Anatomically modern humans likely evolved in Africa and first appear in
the fossil record ~100-120 kYA. Therefore, this population in theory
would represent the last common ancestor for which all modern humans
could trace a common gene pool and ideally could serve as the model for
the genetic nutritional requirements of all present day humans before
the confounding influence of various environments wrought by migration
etc. upon our genome. However, it is inappropriate to dismiss the
nutritional evolutionary experience of all hominids prior to the split
between anatomically modern humans and their predecessors because, we
share more genes with these hominids than those for which we differ.
In order for encephalization (increase in brain size relative to
body mass) to proceed, early hominids had to increase the nutrient
density of their predominantly plant based diets (1). This increase
in the size and metabolic activity of the brain occurred as a result of
a decrease in the size and the metabolic activity of the gut (2). The
most obvious nutrient dense foods that early hominids began to include
in their diet were animal based foods, including scavenged bones
containing marrow and skulls containing brain. Early stone tools
presumably (inferred from cut marks on associated butchered fossil
bones) were manufactured to facilitate the dismembering of either hunted
or scavenged carcasses. This consumption of animal based foods which
led to a relatively smaller and less metabolically active gut is still
with us today. So presumably all hominids (including modern humans)
share the basic gastrointestinal physiology that evolved in response to
a high meat based diet. Further, all modern humans have poor ability
to desaturate and chain elongate 18 carbon lipids to 20 and 22 carbon
lipids (3). Similar to cats (complete carnivores) the inability to
efficiently desaturate and chain elongate plant based 18 carbon lipids
to the 20 and 22 carbon lipids needed for membrane and eicosanoid
function has occurred because the selective pressure for desaturation
and chain elongation has been relaxed. Humans like cats eat higher up
on the food chain (ie. other animals), in which 20 and 22 carbon lipids
are present - thus there is little need to retain genes for lipid
desaturation and chain elongation of plant based 18 carbon lipids.
Similar arguments can be made for the synthesis of taurine (a
conditionally essential amino acid) and the conversion of beta carotene
to vitamin A.
Thus, the basic physiological adaptation to a meat based diet
occurred early on and was likely complete by the time early hominids
migrated to northern latitudes. Fruit eating hominids could not have
left the environs of the tropics until they began to utilize a food
source that was present not only in the tropics but elsewhere. The
remains of archaic humans in Germany ~ 400,000 yrs ago as well as their
wooden hurling spears ( 3 ) clearly indicates that these people were
meat eating hunters, genetically well adapted to their prey. There is
no evidence whatsoever that this pattern of diet in which meat
predominates had changed in Africa at the time of or after the
evolutionary split between anatomically modern humans. In fact, to the
contrary, it appears that anatomically modern humans became even more
efficient hunters as they appeared in the fossil record in europe, asia
and north america. Thus, deviation from these basic dietary patterns
have only occurred relatively recently in the meso and neolithic.
Consequently, it seems likely that there may have been many basic
nutritional similarities between anatomically modern humans and their
predecessors.
REFERENCES
1. Leonard WR et al. Evolutionary perspectives on human nutrition:
the influence of brain and body size on diet and metabolism. Am J Human
Biol 1994;6:77-88.
2. Aiello LC et al. The expensive tissue hypothesis. Curr
Anthropology 1995;36:199-221.
3. Thieme H. Lower palaeolithic hunting spears from Germany.
Nature 1997;385:807-10.
I enjoyed Linda Scott Cummings wonderful post on
pre-agricultural diets in North America during the holocene based upon
her work done with coprolites. I would agree with her that during
this period, there was a world wide increase in the exploitation of
small animals, the aquatic environment and many plant based foods that
was coincident with the extinction of numerous large pleistocene mammals
(1,2). Also, I'm sure that she would agree that the consumption of the
meat or organs of large mammals is still technically difficult or
impossible to determine in coprolites. Also, coprolite evidence
generally could not distinguish the relative timing of plant vs: animal
meal consumption. Clearly a plant based meal followed hours later by
an animal based meal would produce mixed fecal material.
1. Stuart A.J. Mammalian extinctions in the late pleistocene of
northern eurasia and north america. Biol Rev 1991;66:453-62.
2. Webster D, Webster G. Optimal hunting and pleistocene
extinction. Human Ecology 198412:275-89.
I agree with John Blank's mention of the value of carbohydrate
in the consumption of high protein meals. There is an absolute limit
to the amount of non-fat protein which can be consumed, and it has been
estimated to be roughly 300 g and/or 50% of total calories (1). Thus,
there would have been a protein constraint for all humans following the
killing of a large game animal, and they would have had to either
selectively eat fatty portions of the carcass along with the lean meat
or they would have had to include plant based carbohydrate with the lean
meat (but not necessarily at the exact same moment). As John pointed
out, carbohydrate generally will allow a greater protein intake than
will fat. At higher latitudes and during winter months (wherein plant
foods are restricted), the only way out of this protein conundrum is to
selectively eat fatter animals or the fatty portions of the carcass to
the exclusion of the lean meat.
Despite this protein ceiling, a survey of 181 world wide hunter
gatherer societies (2) show that in 61.3% of the societies, plant foods
comprised 35% of less of the total food energy and that the most
frequently occurring plant: animal subsistence ratio would have been
16-25% plant : 66-75% animal.
REFERENCES
1. Speth JD. Early hominid hunting and scavenging: the role of
meat as an energy source. J Hum Evolution 1989;18:329-43.
2. Murdock GP. Ethnographic Atlas: a summary. Ethnology
1967;6:109-236.
In response to Steve Meyers, I stand by my guns that saturated
fat is atherogenic, particularly in western based diets wherein the
protein intake is low (12-15% energy) relative to that which potentially
was available from pre-agricultural diets (35-50%). I have firmly
stated my position on this in my lengthy Oct 9, 1997 post. I agree
with Dr. Millard's conclusion that there are confounding variables which
make the data Enig and Fallon offer difficult to interpret. Stone age
diets, although high in animal based food were low in saturated fat,
even when fattier portions of the carcass were consumed. Our analysis
of the lipid composition of portions of wild animal carcass which we
recently presented in Bethesda (1) confirm this concept. The combined
total amount of polyunsaturated and monounsaturated fat in wild animals
would have almost always equaled or exceed the saturated fat content.
REFERENCES
1. Cordain L et al. The fatty acid composition of muscle, brain,
marrow and adipose tissue in elk: evolutionary implications for human
dietary lipid requirements. World Rev Nutr Diet 1998, in press.
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