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Cunnane
[Survival of the fattest: the key to human brain evolution]
Cunnane SC.
Med Sci (Paris). 2006 Jun-Jul;22(6-7):659-63. Review. French.
[abstract only]
"The circumstances of human brain evolution are of central importance to accounting for human origins, yet are still poorly understood. Human evolution is usually portrayed as having occurred in a hot, dry climate in East Africa where the earliest human ancestors became bipedal and evolved tool-making skills and language while struggling to survive in a wooded or savannah environment. At least three points need to be recognised when constructing concepts of human brain evolution : (1) The human brain cannot develop normally without a reliable supply of several nutrients, notably docosahexaenoic acid, iodine and iron. (2) At term, the human fetus has about 13 % of body weight as fat, a key form of energy insurance supporting brain development that is not found in other primates. (3) The genome of humans and chimpanzees is <1 % different, so if they both evolved in essentially the same habitat, how did the human brain become so much larger, and how was its present-day nutritional vulnerability circumvented during 5-6 million years of hominid evolution ? The abundant presence of fish bones and shellfish remains in many African hominid fossil sites dating to 2 million years ago implies human ancestors commonly inhabited the shores, but this point is usually overlooked in conceptualizing how the human brain evolved. Shellfish, fish and shore-based animals and plants are the richest dietary sources of the key nutrients needed by the brain. Whether on the shores of lakes, marshes, rivers or the sea, the consumption of most shore-based foods requires no specialized skills or tools. The presence of key brain nutrients and a rich energy supply in shore-based foods would have provided the essential metabolic and nutritional support needed to gradually expand the hominid brain. Abundant availability of these foods also provided the time needed to develop and refine proto-human attributes that subsequently formed the basis of language, culture, tool making and hunting. The presence of body fat in human babies appears to be the product of a long period of sedentary, shore-based existence by the line of hominids destined to become humans, and became the unique solution to insuring a back-up fuel supply for the expanding hominid brain. Hence, survival of the fattest (babies) was the key to human brain evolution."
There's something fishy about human brain evolution
Cunnane S
Public release date: 18-Feb-2006
"Aquatic foods are also rich in iodine, a key brain nutrient. Iodine is present in much lower amounts from terrestrial food sources such as mammals and plants.
It was this combination of abundant shoreline food and the "brain selective nutrients" that sparked the growth of the human brain, he says.
"Initially there wasn't selection for a larger brain," argues Dr. Cunnane. "The genetic possibility was there, but it remained silent until it was catalyzed by this shore-based diet."
Dr. Cunnane acknowledges that for the past 20 years he's been swimming upstream when it comes to convincing anthropologists of his position, especially that initial hominid brain expansion happened by chance rather than adaptation.
But, he says, the evidence of the importance of key shoreline nutrients to brain development is still with us – painfully so. Iodine deficiency is the world's leading nutrient deficiency. It affects more than a 1.5 billion people, mostly in inland areas, and causes sub-optimal brain function. Iodine is legally required to be added to salt in more than 100 countries.
Says Dr. Cunnane: "We've created an artificial shore-based food supply in our salt."
Omega-3 fatty acids, energy substrates, and brain function during aging.
Freemantle E, Vandal M, Tremblay-Mercier J, Tremblay S, Blachere JC, Begin ME, Brenna JT, Windust A, Cunnane SC.
Prostaglandins Leukot Essent Fatty Acids. 2006 Sep;75(3):213-20. Epub 2006 Jul 7. Review.
[abstract only]
"The maintenance of optimal cognitive function
is a central feature of healthy aging. Impairment in brain glucose
uptake is common in aging associated cognitive deterioration, but
little is known of how this problem arises or whether it can be
corrected or bypassed. Several aspects of the challenge to providing
the brain with an adequate supply of fuel during aging seem to relate
to omega-3 fatty acids. For instance, low intake of omega-3 fatty
acids, especially docosahexaenoic acid (DHA), is becoming increasingly
associated with several forms of cognitive decline in the elderly,
particularly Alzheimer's disease. Brain DHA level seems to be an
important regulator of brain glucose uptake, possibly by affecting the
activity of some but not all the glucose transporters. DHA synthesis
from either alpha-linolenic acid (ALA) or eicosapentaenoic acid (EPA)
is very low in humans begging the question of whether these DHA
precursors are likely to be helpful in maintaining cognition during
aging. We speculate that ALA and EPA may well have useful supporting
roles in maintaining brain function during aging but not by their
conversion to DHA. ALA is an efficient ketogenic fatty acid, while EPA
promotes fatty acid oxidation. By helping to produce ketone bodies,
the effects of ALA and EPA could well be useful in strategies intended
to use ketones to bypass problems of impaired glucose access to the
brain during aging. Hence, it may be time to consider whether the main
omega-3 fatty acids have distinct but complementary roles in brain
function."
Survival of the Fattest: The Key to Human Brain Evolution
Cunnane S
Book 2005
In this book by Cunnane on how the human brain evolved, he focuses a great deal on shoreline nutrients -- especially iodine. He has an entire chapter on iodine, as well as another chapter on other key minerals.
Chapter 6. Iodine: The primary brain selective nutrient (pp 115-130)
Chapter 7. Iron, copper, zinc, and selenium: The other brain selective minerals (pp 131-150)
Origins and evolution of the Western diet: implications of iodine and seafood intakes for the human brain.
Cunnane SC.
Am J Clin Nutr. 2005 Aug;82(2):483; author reply 483-4.
"Cordain et al are to be congratulated on a succinct and topical overview, recently published in the Journal, of the perils of a Westernized diet with respect to the risk of chronic degenerative diseases in humans. Indeed, there is widespread support for reinstituting several aspects of the so-called Paleolithic diet, especially higher fiber and lower content of refined, adulterated, or synthetic constituents. However, the authors do not seem to have made reference in their article to the effect of diet on a defining feature of modern humans—namely, the brain—whether that effect is related to brain development, advanced brain function, or risk of degenerative brain disease. Several micronutrients are discussed, but iodine seems to have been overlooked, despite the fact that it is 1 of the 2 nutrients (the other is iron) from which humans globally are considered to suffer the most common deficiency.
"The most serious consequence of iodine deficiency is impaired neurologic development, a problem that most developed countries have avoided only by legislating the use of iodized table salt; commonly preferred food choices that exclude seafood simply do not provide enough iodine. Indeed, publications from Australia, the United States, and Europe during the past decade show that mild-to-moderate iodine deficiency is reemerging as people in developed countries consume less table salt, dairy products, meat, fish, and seafood.
"Cordain et al gave an overview of the nutrient density in various major food groups in Table 4 of their article, but they made no mention of the relatively poor bioavailiability of micronutrients, especially minerals, from some of these food groups. The concentration in plants of zinc or iron, without consideration of the phytate content of those plants, exaggerates the true value of plants as sources of these nutrients. Although iodine is not shown in Table 4, goitrogens in many cultivated plants greatly reduce the availability of iodine from plant-based diets. Hence, the overall ranking in Table 4 of seafood second to vegetables as a source of micronutrients underestimates the true value of seafood in protecting against the risk of the major nutrient deficiencies that affect humans. Among the food groups shown in the table, seafood actually has the highest available content of several minerals needed for brain development, including iodine, iron, zinc, copper, and selenium.
"The focusing of some attention on the human health implications of declining iodine and seafood intakes is warranted because those declining intakes are directly linked to brain development. The modern-day vulnerability of the developing human brain to inadequate intakes of iodine, iron, docosahexaenoic acid, and several other brain-selective nutrients shows that, if seafood had not been a significant component of the Paleolithic diet, the modern human brain probably would not have evolved in the first place."
Problems with essential fatty acids: time for a new paradigm?
Cunnane SC.
Prog Lipid Res. 2003 Nov;42(6):544-68. Review.
[abstract only]
"The term 'essential fatty acid' is ambiguous and inappropriately inclusive or exclusive of many polyunsaturated fatty acids. When applied most rigidly to linoleate and alpha-linolenate, this term excludes the now well accepted but conditional dietary need for two long chain polyunsaturates (arachidonate and docosahexaenoate) during infancy. In addition, because of the concomitant absence of dietary alpha-linolenate, essential fatty acid deficiency is a seriously flawed model that has probably led to significantly overestimating linoleate requirements. Linoleate and alpha-linolenate are more rapidly beta-oxidized and less easily replaced in tissue lipids than the common 'non-essential' fatty acids (palmitate, stearate, oleate). Carbon from linoleate and alpha-linolenate is recycled into palmitate and cholesterol in amounts frequently exceeding that used to make long chain polyunsaturates. These observations represent several problems with the concept of 'essential fatty acid', a term that connotes a more protected and important fatty acid than those which can be made endogenously. The metabolism of essential and non-essential fatty acids is clearly much more interconnected than previously understood. Replacing the term 'essential fatty acid' by existing but less biased terminology, i.e. polyunsaturates, omega3 or omega6 polyunsaturates, or naming the individual fatty acid(s) in question, would improve clarity and would potentially promote broader exploration of the functional and health attributes of polyunsaturated fatty acids."
Survival of the fattest: fat babies were the key to evolution of the large human brain.
Cunnane SC, Crawford MA.
Comp Biochem Physiol A Mol Integr Physiol. 2003 Sep;136(1):17-26. Review.
[abstract only]
" In the past 2 million years, the hominid lineage leading to modern humans evolved significantly larger and more sophisticated brains than other primates. We propose that the modern human brain was a product of having first evolved fat babies. Hence, the fattest (infants) became, mentally, the fittest adults. Human babies have brains and body fat each contributing to 11-14% of body weight, a situation which appears to be unique amongst terrestrial animals. Body fat in human babies provides three forms of insurance for brain development that are not available to other land-based species: (1) a large fuel store in the form of fatty acids in triglycerides; (2) the fatty acid precursors to ketone bodies which are key substrates for brain lipid synthesis; and (3) a store of long chain polyunsaturated fatty acids, particularly docosahexaenoic acid, needed for normal brain development. The triple combination of high fuel demands, inability to import cholesterol or saturated fatty acids, and dependence on docosahexaenoic acid puts the mammalian brain in a uniquely difficult situation compared with other organs and makes its expansion in early humans all the more remarkable. We believe that fresh- and salt-water shorelines provided a uniquely rich, abundant and accessible food supply, and the only viable environment for evolving both body fat and larger brains in human infants."
Brain-specific lipids from marine, lacustrine, or terrestrial food resources: potential impact on early African Homo sapiens.
Broadhurst CL, Wang Y, Crawford MA, Cunnane SC, Parkington JE, Schmidt WF.
Comp Biochem Physiol B Biochem Mol Biol. 2002 Apr;131(4):653-73. Review.
[abstract only]
"The polyunsaturated fatty acid (PUFA) composition of the mammalian central nervous system is almost wholly composed of two long-chain polyunsaturated fatty acids (LC-PUFA), docosahexaenoic acid (DHA) and arachidonic acid (AA). PUFA are dietarily essential, thus normal infant/neonatal brain, intellectual growth and development cannot be accomplished if they are deficient during pregnancy and lactation. Uniquely in the human species, the fetal brain consumes 70% of the energy delivered to it by mother. DHA and AA are needed to construct placental and fetal tissues for cell membrane growth, structure and function. Contemporary evidence shows that the maternal circulation is depleted of AA and DHA during fetal growth. Sustaining normal adult human brain function also requires LC-PUFA.Homo sapiens is unlikely to have evolved a large, complex, metabolically expensive brain in an environment which did not provide abundant dietary LC-PUFA. Conversion of 18-carbon PUFA from vegetation to AA and DHA is considered quantitatively insufficient due to a combination of high rates of PUFA oxidation for energy, inefficient and rate limited enzymatic conversion and substrate recycling. The littoral marine and lacustrine food chains provide consistently greater amounts of pre-formed LC-PUFA than the terrestrial food chain. Dietary levels of DHA are 2.5-100 fold higher for equivalent weights of marine fish or shellfish vs. lean or fat terrestrial meats. Mammalian brain tissue and bird egg yolks, especially from marine birds, are the richest terrestrial sources of LC-PUFA. However, land animal adipose fats have been linked to vascular disease and mental ill-health, whereas marine lipids have been demonstrated to be protective. At South African Capesites, large shell middens and fish remains are associated with evidence for some of the earliest modern humans. Cape sites dating from 100 to 18 kya cluster within 200 km of the present coast. Evidence of early H. sapiens is also found around the Rift Valley lakes and up the Nile Corridor into the Middle East; in some cases there is an association with the use of littoral resources. Exploitation of river, estuarine, stranded and spawning fish, shellfish and sea bird nestlings and eggs by Homo could have provided essential dietary LC-PUFA for men, women, and children without requiring organized hunting/fishing, or sophisticated social behavior. It is however, predictable from the present evidence that exploitation of this food resource would have provided the advantage in multi-generational brain development which would have made possible the advent of H. sapiens. Restriction to land based foods as postulated by the savannah and other hypotheses would have led to degeneration of the brain and vascular system as happened without exception in all other land based apes and mammals as they evolved larger bodies."
Hunter-gatherer diets-a shore-based perspective.
Cunnane SC.
Am J Clin Nutr. 2000 Dec;72(6):1584-8.
" We argue that the shore-based ecologic niche was uniquely able to stimulate expansion of the primate brain because, in addition to being a plentiful supply of dietary energy and protein, it provided certain brain-selective nutrients, such as docosahexaenoate, iodine, zinc, copper, and iron. The basis for this hypothesis is that terrestrial foods are deficient in iodine and contain little docosahexaenoate (only in animal tissue). Zinc, copper, and iron are more abundant and available from seafood than from plants. Dietary or genetically imposed deficiencies of all of these brain-selective nutrients leaves the modern human brain extremely vulnerable to subnormal development. Equally important is the issue of access to reliable sources of foods rich in brain-selective nutrients that required minimal effort to locate and consume. Such foods would have to have been available for thousands of years before intelligence had risen sufficiently to conceive of and experiment successfully with true fishing or hunting and trapping of wild animals. The hominid fossil record shows that at least fish and shellfish—but probably also eggs, amphibians, and plants on lakeshores and seacoasts—provided an abundance of this important dietary stimulus for human brain evolution without special effort or substantial competition from predators .
"If the nutrient and energy supplies were consistently inadequate in some geographic areas over thousands of years, human brain evolution would have faltered and long-term colonization of those areas would have ceased until the appropriate foods were found or supplements were invented. This is what happened most clearly with iodine deficiency, which affects more than a billion mostly vegetarian people in inland areas of all continents. Iodine is essential for energy metabolism, normal brain development, and fertility. People can survive even severe iodine deficiency but they cannot thrive or reproduce. In contrast, coastal peoples experience no known nutrient deficiencies affecting brain function. Hence, as we argued, marine, estuarine, and lacustrine locations probably favored human brain evolution by providing abundant energy and protein but, equally importantly, brain-selective nutrients."
Rift Valley lake fish and shellfish provided brain-specific nutrition for early Homo.
Broadhurst CL, Cunnane SC, Crawford MA.
Br J Nutr. 1998 Jan;79(1):3-21. Review.
[abstract only]
"An abundant, balanced
dietary intake of long-chain polyunsaturated fatty acids is an
absolute requirement for sustaining the very rapid expansion of the
hominid cerebral cortex during the last one to two million years. The
brain contains 600 g lipid/kg, with a long-chain polyunsaturated fatty
acid profile containing approximately equal proportions of arachidonic
acid and docosahexaenoic acid. Long-chain polyunsaturated fatty acid
deficiency at any stage of fetal and/or infant development can result
in irreversible failure to accomplish specific components of brain
growth. For the past fifteen million years, the East African Rift
Valley has been a unique geological environment which contains many
enormous freshwater lakes. Paleoanthropological evidence clearly
indicates that hominids evolved in East Africa, and that early Homo
inhabited the Rift Valley lake shores. Although earlier hominid
species migrated to Eurasia, modern Homo sapiens is believed to have
originated in Africa between 100 and 200 thousand years ago, and
subsequently migrated throughout the world. A shift in the hominid
resource base towards more high-quality foods occurred approximately
two million years ago; this was accompanied by an increase in relative
brain size and a shift towards modern patterns of fetal and infant
development. There is evidence for both meat and fish scavenging,
although sophisticated tool industries and organized hunting had not
yet developed. The earliest occurrences of modern H. sapiens and
sophisticated tool technology are associated with aquatic resource
bases. Tropical freshwater fish and shellfish have long-chain
polyunsaturated lipid ratios more similar to that of the human brain
than any other food source known. Consistent consumption of lacustrine
foods could have provided a means of initiating and sustaining
cerebral cortex growth without an attendant increase in body mass. A
modest intake of fish and shellfish (6-12% total dietary energy
intake) can provide more arachidonic acid and especially more
docosahexaenoic acid than most diets contain today. Hence,
'brain-specific' nutrition had and still has significant potential to
affect hominid brain evolution."