The usual nutrient
mentioned for big brains is alpha-linolenic acid (ALA) one of two
essential fatty acids, the other being linoleic acid (LA). ALA is
important because it elogates to EPA and DHA (docosohexaenoic acid)
and DHA is a vital component in nervous tissue. However, since ALA
is only synthesized in the chloroplasts of green plants I see no
particular reason why meat eating would provide more DHA since the
highest sources of DHA are flaxseed, soy, and green plants and we
can make our own DHA from the plant source ALA that we eat on a
greens based diet (not however on a grains based diet which is only
high in LA ).
may have been referring to the social advantages and problem solving
requirements of hunting. If so I would agree that hunting conferred
a selective advantage on those who hunted since one must outsmart
the prey and then devise techniques to bring it back to camp. Meat
eating also provides more Calories than plant gathering and that
would also confer an enormous advantage in primitive times.
Here is an interesting
website run by Tom Billings, a vegetarian who specializes in debunking
bogus claims by other vegetarians. If I read his intent correctly
he's saying that while we have the enzymes necessary to elongate
ALA to DHA we can't do it fast enough to match the DHA content in
meat. I regard this as possible but not probable except in infants
who lack the necessary enzymes and must have preformed DHA either
from breast or cow's milk. If however the allegation is correct
then flax oil consumption is one option for committed vegans and
"Neuromins" capsules that contain DHA made by algae are
I tried the
Neuromins myself for a couple of months but it didn't make me any
dependent on preformed long-chain fatty acids such as DHA. The most
plausible current hypothesis for the biological mechanism(s) responsible
for the absolute decrease in brain size is that the shortfall in
consumption of animal foods since the late Paleolithic has brought
with it a consequent shortfall in consumption of preformed long-chain
fatty acids [Eaton and Eaton 1998]. Specifically, for optimal growth,
the brain is dependent on the fatty acids DHA (docosahexaenoic acid),
DTA (docosatetraenoic acid), and AA (arachidonic acid) during development
to support its growth during the formative years, particularly infancy.
These are far more plentiful in animal foods than plant.
Eaton et al.
 analyze the likely levels of intake of EFAs involved in brain
metabolism (DHA, DTA, AA) in prehistoric times, under a wide range
of assumptions regarding possible diets and EFA contents. Their
model suggests that the levels of EFAs provided in the prehistoric
diets was sufficient to support the brain expansion and evolution
from prehistoric times to the present, and their analysis also suggests
that the current low levels of EFA intake (provided by agricultural
diets) may explain the recent smaller human brain size.
Rate of synthesis
of DHA from plant-food precursors does not equal amounts available
in animal foods. Although the human body will synthesize long- chain
fatty acids from precursors in the diet when not directly available,
the rates of synthesis generally do not support the levels obtained
when they are gotten directly in the diet. This is particularly
critical in infancy, as human milk contains preformed DHA and other
long-chain essential fatty acids, while plant-food based formulas
do not (unless they have been supplemented).
indicate that synthesis of DHA from plant-source precursor fatty
acids does not equal the levels of DHA observed when those are included
in the diet: Anderson et al.  as cited in Farquharson et al.
, Anderson and Connor , Woods et al. . Similar
results are reported from studies using human infants as subjects:
Carlson et al. , Farquharson et al. , Salem et al. .
For a discussion of the above studies, plus additional studies showing
low levels of EFAs in body tissues of vegans, see Key Nutrients
vis-a-vis Omnivorous Adaptation and Vegetarianism: Essential Fatty
To summarize <http://www.beyondveg.com/graphics/shim.gif>
The data that human brain size has fallen 11% in the last 35,000
years--with the bulk of that decrease (8%) coming in the last 10,000
years-- furnishes, by extension, suggestive, potential corroborative
support for the hypotheses explored earlier in this section that
increasing brain development earlier in human evolution is correlated
positively with the level of animal food in the diet. It also indicates
that animal food may be a key component of dietary quality (DQ)
that cannot be fully substituted for by increasing other components
in the diet in its absence (such as grains).
is important to consider, because evidence available on the changes
in food practices of more recent prehistoric humans (and of course,
humans today) can be assessed in more depth and with a higher degree
of resolution than dietary inferences about earlier humans. In conjunction
with data about DHA synthesis in the body vs. obtaining it directly
from diet, this provides a potentially important point of comparison
for assessing hypotheses about the brain/diet connection.
received a degree in physics from the University of California Berkeley,
where he earned Phi Beta Kappa honors. He received his degree in
medicine from the University of California at San Francisco, and
received his postgraduate training at San Diego County Hospital.
He holds a Medical License in the State of Hawaii. He has been an
Emergency Department physican since 1963, and the Director of the
Kaiser Permanente Vegan Lifestyle Clinic on Oahu until his retirement
in 1998. Dr. Harris is the author of The Scientific Basis of Vegetarianism.
addition, he was the 1950 Big Ten Trampoline Champion, is an accomplished
hangglider and commercial pilot, and at age 70 became a skydiver
with 108 jumps to date. Dr. Harris has been vegetarian since 1950,
and vegan since 1963.