Fats & The Brain 1 - Why DHA Matters

The Human Brain is

An unappetising 1.3-kg (3-lb) mass of pinkish-gray jellylike tissue made up of approximately 100 billion* nerve cells, or neurons; neuroglia (supporting-tissue) cells; and vascular (blood-carrying) and other tissues.

A piece of meat providing ~1850 calories - enough energy to keep an 'average' human being going for about 18 hours. About 450 of those calories are needed to keep the 'average' human being's own brain going.

* The number of human brain cells is a very moot point. Nobody's ever counted them - if they did, at 100 per second, it would take them about 317 years - (Typical of the sort of nutty trivia you get in these expositions).

Please bear with me while we go through the basic biochemics:

A brain cell, structurally, is pretty much the same as any other. Its walls (much of its 'dry weight') are made of phospholipids and cholesterol - fats.

Note the structural importance of phospholipids, but note also the essential part played in the structure by cholesterol. 

A brain cell's functions are, to be sure, somewhat more complicated, but only its structure is what concerns us here. 

Here I should give a little credit to Mr William Gates, whose on-line encyclopedia, Encarta, has some pretty illustrations, but is so politically correct and aligned towards US American biasses that it is quite useless for the rest of the world.  Where I have used his pretty pictures, I have cropped them to remove the unsightly copyright injunctions.

Much better is Wikipedia, an open, free, and truly democratic on-line reference resource.

Fats in the body have different forms:

Triglycerides

3 fatty 'acids' joined to a glycerol bond - fats stored as droplets, and used only for energy. 

Phospholipids

2 fatty 'acid' molecules only, always including phosphorous. The 'tadpoles' making up the cell membrane are fatty acid molecules, and face in and out - they keep out unwanted substances, but also transmit electrical messages.

Cholesterol

Another essential structural 'chemical fat', but this time a sterol, or complex alcohol compound, with no fatty acids. It's fairly inert, but absolutely essential as a structural element of cells, and especially for nerve cell insulation.

As fat molecules get longer, they also get more and more complex. 
Fats in our normal diet can have 16, 18 or up to 22 carbon atoms in the chain. 

Saturates, Monounsaturates, and Polyunsaturates

Saturated 

All carbon atoms in the chain, except the two end ones, have two carbon molecule partners and two hydrogens.

The simpler they are, the more easily they pack together, so they are solid at room temperatures

Mono-unsaturated

One pair of carbon atoms in the chain are incestuous - they link to each other.

When they start committing incest (double carbon bonds) they begin to get kinky (Don't all incestuous couples?), and don't pack together with the gang. So they're more often liquid at room temperatures.

Poly-unsaturated

More incest - two or more double carbon bonds. 

When you start committing multiple incest, and also have the opportunity to go Left or Right, you get all the complications of PUFAs.

Just as multiple incest and Left and Right add to the gaiety of Life and Politics, the complications of PUFAs are essential to their physical functions.

Trans Fats

Are wholly artificial saturated fats, made by hydrogenating (ie boiling, catalysing, and generally messing up cheap unsaturated vegetable oils) in the name of profit, due to an American idiosyncrasy for solid fats (shortening) for cooking, and because many of them have been convinced by propaganda that margarine and the stuff that snacks are fried in were devised by kind-hearted, concerned industrialists as healthy alternatives to natural butter.

see:

Diversion on Cholesterol

Trans fats. What are trans fats? Trans fat effects, sources of trans fat

The commonest Poly-Unsaturated Fatty Acids  (PUFAs) are: 

Systematic name

Trivial name

Shorthand 

Omega 6

9,12-octadecadienoic

linoleic LA

Mammals cannot make this for themselves, and must get it from food.

18:2(n-6)

6,9,12-octadecatrienoic

g-linolenic

18:3(n-6)

8,11,14-eicosatrienoic

dihomo-g-linolenic

20:3(n-6)

5,8,11,14-eicosatetraenoic

arachidonic AA

Major constituent of membrane lipids (phospholipids) and principal precursor by enzymatic action of the hormone-like eicosanoids including the prostaglandins

20:4(n-6)

7,10,13,16-docosatetraenoic

22:4(n-6)

4,7,10,13,16-docosapentaenoic

22:5(n-6)

Omega 3

9,12,15-octadecatrienoic

a-linolenic ALA

Only in plants, but the body has enzymes that can convert a-linolenic to EPA.

18:3(n-3)

6,9,12,15-octadecatetraenoic

stearidonic

18:4(n-3)

8,11,14,17-eicosatetraenoic

-

20:4(n-3)

5,8,11,14,17-eicosapentaenoic

EPA

In unicellular marine algae, brown macroalgae, in moss cells and in many animal tissues (mainly in nervous tissues)

20:5(n-3)

7,10,13,16,19-docosapentaenoic

DPA

22:5(n-3)

The most abundant fatty acid in the vertebrate brain and found in abundance in fish and shellfish. 

Omega 9

5,8,11-eicosatrienoic

Mead acid

20:3(n-9)

polyenoic fatty acids  A comprehensive list of all dietary fatty acids is available at: www.nutritiondata.com

"DHA is the most abundant fatty acid in the vertebrate brain. Several studies have shown that DHA is itself necessary to support optimal function of the brain and retina (Mitchell DC et al. Biochem Soc Trans 1998,). They are important components of fish oil triacylglycerols and their health benefits are claimed to be diverse and orientated against many human disorders

(see the site "Fats of Life"). 

It was also suggested that the evolution of the large human brain depended on a rich source of DHA from vegetal or animal food (Crawford MA et al., OCL 2004)".

 polyenoic fatty acids

DHA looks like this under a microscope - hardly relevant but pretty.

Linoleic (omega-6) and alpha-linolenic (omega-3) PUFAs cannot be made by the body, and must be obtained from food - linoleic from plants, and alpha-linolenic also from marine algae and animals - mostly nervous tissue.

The only pathways to achieving a higher intake of DHA, sufficient to evolve a larger human brain, would be to eat marine algae, or animals which eat it (or animals which eat them) or eat a great deal of animal nervous tissue. 

Why is DHA so essential? 

So the faster an animal grows, the larger it becomes and the greater is the constraint of the biosynthesis of AA and DHA. The large savanna mammals of Africa all shared the same fate, namely DHA and brain capacity declined as body size accelerated. The important issue is that desaturation and elongation in these large mammals peters out at w3DPA with relatively little DHA being synthesized. What little DHA is synthesized is used in the brain and photoreceptor. The abundant w3DPA is not found here. Brain size was sacrificed not brain DHA. 

2. Allow for substantial amounts of 18 carbon polyunsaturated fatty acids (PUFA) which would have been oxidised for energy requirements. 

3. Explain and allow for our inefficient conversion of 18:2(n-6) Linoleic acid to 20:4(n-6) Arachidonic acid - AA, and 18:3(n-3) a-linolenic acid to DHA (which is illustrated by preferential incorporation of DHA in the infant brain and improved problem solving in infants fed DHA which persisted beyond the period of supplementation).

Why has DHA been chosen so overwhelmingly for photoreceptor and synaptic membranes, despite the availability of similar molecules which would be less difficult to obtain, and are less vulnerable to oxidative damage? In particular, what advantage does it convey  relative to the very closely related w3 and w6 DPAs, each of which differs from DHA only in the absence of one double bond (between carbons 4 -5, and 19-20, respectively)?

As described above, Nature’s preference for DHA in the brain is strikingly demonstrated in large land mammals, in which DPA is the dominant w3 metabolite yet neural membranes still retain the DHA-rich composition observed in other species (possibly at the expense of gross brain size, since DHA is in such limited supply). Significant quantities of the w6 form of DPA are observed only in situations of artificial w3 deficiency, yet even here brain membranes are resistant to decreases in their DHA levels. Nature is thus highly sensitive to the slight difference between DHA and DPA molecules; the presence of DHA’s full complement of six double bonds is for some reason an important priority in neural membranes.

In summary, a number of studies have been conducted on the physical effects of polyunsaturation on membranes, in which DHA has been compared to a range of other unsaturated chains having from one to five double bonds. Thus far, however, all differences that have been measured have been matters of degree, and none provide a compelling explanation for the striking specificity with which DHA is selected for membranes of the eye and brain. In addition, to our knowledge no study has compared DHA to either species of DPA to search for whatever property it is that causes neural membranes to discriminate so clearly between these seemingly similar molecules.

Crawford et al  (2004) Evidence for the unique function of DHA during the evolution of the modern hominid brain. 

Michael Crawford was perhaps the first leading dietary scientist to notice the gross flaws in the 'current paradigm' of human evolution, based on the presumption that Early Humans hunted or scavenged big game, originally on the 'Savannah' but more recently in the 'open woodlands' of East Africa, the classical site for most Early Human fossil finds.

See The Skull & Bones Club

As 'only a dietician' his views could be ignored by real palaeoanthropologists, if it wasn't for the fact that they have a solid basis in his own early experiences in East Africa.

And he's not 'only a dietician' - the thrust of his professional work has been to investigate the importance of DHA in developing the human brain, and in particular, its practical, current application to saving and improving the lives of newborn infants.

He tells of his early conversion in his PDF paper - Crawford MA (2004) Docosahexaenoic acid and the evolution of the brain - a message for the future. Lipid Technology 16(3):

Regrettably, it's one of those PDFs that don't export to a text format for easy plagiarism, and I don't intend to transliterate it word for word, so here's a précis:

Mammal brains grow, but then meet a bottleneck

Omega 3 fatty acids have been an essential part of vertebrate brains since the very first vertebrate brain appeared in the fossil record - the early fish Haikouichthys - about 500 Mya.

Omega 3 fatty acids have always been predominant in the marine food chain.

(I'm frankly not sure, and can't quote chapter and verse, but I've got a feeling that the very same fatty acid compounds were used by marine invertebrate nervous systems for quite some time before). 

Omega 6 fatty acids, although they've probably long been used by some of the unicellular organisms who really rule the earth, only appeared noticeably (to us) when flowering plants (Angiosperms) evolved a way of enclosing their seeds (embryo offspring) in a protective carpel, and needed a fatty acid energy supply to endow them with. Flowering plants appeared only ~140Mya.

There's not a lot of DHA or its precursors around in inland terrestrial areas, so Omega 6 fats were utilised instead. That is why many seed oils (soy, palm, canola, etc) are very much richer in Omega 6 than most animal fats.

Mammalian brain size is larger in relation to body size compared to the previous egg laying amphibians, reptiles and fish. The difference could be explained by the evolution of the placenta. The placenta enables nutrients and energy to be focused continuously on the development of one or a small number of progeny throughout the critical time of brain development. In the human, 70% of the calories transferred by the placenta to the fetus is devoted to brain growth. The placenta is a rapidly growing vascular system with a high requirement for w6 fatty acids especially AA. In 42 species so far studied, AA and DHA are major acyl constituents with the precursors being virtually absent. So the emergence of the w6 fatty acids may have added the missing biochemical link, liberating genetic potentials for vascular development and hence the evolution of the placenta, mammary gland and the larger brains of the mammals.
Evidence for the unique function of DHA during the evolution of the modern hominid brain.
Crawford MA, et al  (2004) 

Diversion on grasses

Just a very few million years later, in the 38-24Mya Oligocene, grazing animals began to evolve to feed on the growing resource of grasslands taking over from forests as the overall continental climate cooled and dried.

During the Miocene (24 to 5Mya) grasses continued to take over from forests, worldwide.

At some time during that vast 40 million years, some grass eaters evolved an extra 'stomach'; the rumen, with a host of symbiotic organisms that help them make the very best of the poor nutrients in grass. 
They started to chew the cud.

Around 2-3Mya, ruminants started to proliferate in certain parts of Africa, as Elizabeth Vrba has documented. This is about the same time as Early Humans began to emerge. 

Mammal brains grow, but then meet a bottleneck

What do the adherents of the 'current paradigm' say ?

Dr Loren Cordain says
"As mammals evolve larger bodies, encephalization quotients (brain mass/body mass) generally decrease, consequently evolving mammalian brains were not able to maintain their relative mass with greater and greater evolutionary increases in body mass. This limitation occurs because the supply of the fatty acid building blocks for brain tissue (AA and DHA) is constrained by the limited ability of the liver (primarily) and other tissues to synthesize these fatty acids from their dietary precursors. 

Numerous studies in mammals, including humans, have shown that the elongation and desaturation of linoleic acid (18:2n6) to AA and of alpha-linolenic acid (18:3n3) to DHA are inefficient pathways with low product to substrate ratios. Hence, the limited availability of these two fatty acids from endogenous metabolic synthesis may have represented the evolutionary ‘bottleneck’ impeding the encephalization process in all herbivorous mammals."

Cordain L, Watkins BA, Mann NJ.

Fatty acid composition and energy density of foods available to African hominids

But Dr. Cordain isn't one to give up easily. He goes on to say:

"Cats and other obligate carnivores represent a notable departure from the metabolic and evolutionary considerations that limit brain size in herbivorous animals because they obtain virtually all of their AA and DHA as preformed product in the flesh and organs of their prey and are only minimally reliant upon elongation and desaturation of 18 carbon fatty acids as their source of AA and DHA. Throughout evolutionary history, carnivorous mammals have always maintained a proportionately larger brain size relative to body size when compared to their herbivorous prey. The dietary availability of preformed AA and DHA is exclusive to meat eaters, since these fatty acids are not present or present only in trace quantities in plant food sources.

In a similar manner, increasing consumption of animal food products also provided early hominids with a dietary source of preformed AA and DHA, substances that may have opened the evolutionary ‘window’ for encephalization".

Cordain L, Watkins BA, Mann NJ. Fatty acid composition and energy density of foods available to African hominids

You can read about Dr Loren Cordain's professional interests at: 

Paleo Diet Articles, High Protein Diets, Low Carbohydrate Diets

If both herbivores and carnivores had a hard time growing bigger brains on the savannah (or open woodlands) of East Africa, just how did 5ft high hominids do any better?

Where did we get our DHA for early brain development?

The Skull & Bones Club, staunch defenders of the paradigm of Early Human big-game eating, propose that Early Humans got their DHA from:

- scavenged carcasses.

"With the emergence of species of the genus homo at least 2-3 million years ago, a rapid increase in brain mass relative to body mass (encephalization) occurred. The selective pressure that allowed for this increase in brain size is attributed to the improvement in dietary quality that involved both higher energy density and abundance of preformed long chain polyunsaturated fatty acids (LCPUFAs), such as docosahexaenoic acid (DHA) and arachidonic acid (AA), which dominate brain phospholipid (pl) composition. 

To establish the likely range of foods leading to this process, the nutrient composition of a wide range of African ruminant tissues (brain, marrow, etc) freshwater fish, and edible wild plants were investigated.

Ruminant subcutaneous fat and marrow and wild plants were found to be insignificant dietary sources of DHA and AA. The richest source of DHA and AA was ruminant brain tissue.

African field studies on carcass composition of large herbivores consumed by carnivores indicate that bone marrow (energy dense) and brain tissue (AA, DHA rich) were the items most likely left by carnivores. Hence these parts would be the most frequently available to prehistoric hominid scavengers. Freshwater fish most certainly would contribute adequate AA and DHA at sufficient levels for encephalization, however they would fail to meet hominid energy requirements, due to their low energy density (119 kcal/100g). 

In conclusion it seems likely that evolving hominids consumed scavenged ruminant brain tissue as a rich source of AA and DHA and bone marrow as a principle energy source for the evolution of a large metabolically active brain".

Evolutionary Implications for Human Brain Development and Fatty Acid Intake (Abstract). 

This sounds entirely reasonable, but there are significant omissions:

1

Size of 'average' African ruminant brain is not quoted.

Very few papers available to me on the internet (my only major library resource) show the actual brain weights of African ruminants, but Brummelkamp (1940) listed weights of several. As you can see, they vary widely.

Using the detailed figures quoted in another of Cordain et al's papers:

Fatty Acid Composition and Energy Density of Foods Available to African Hominids,

I have combined their AA and DHA average values with Brummelkamp's brain sizes, to get an idea of the absolute brain yield from each type of carcass. 

I have also used the same figures as quoted by them, for an 'average African freshwater fish' to calculate the equivalents of how many one-pounder fish would be needed to give the same fatty acid as each single 'African ruminant' brain.

I'm no Izaak Walton, and I can't angle for peanuts, but, every day, local kids bring me at least a pound of hand-caught fish, to feed my fish owl, two water monitors, a goshawk, a heron, and a water dragon. It shouldn't be too difficult for Early Humans to hand-catch fish. And indeed, for them it wasn't.

See: Shoreline Reptiles and Where's the Evidence?

If the conventional big game meat-eating paradigm is to survive it will have to do a bit better than suggest that Early Humans caught as many Oryx (or half as many Hippopotami) for every one-pounder fish to obtain their extra requirements of DHA and get as clever as we think we are.

2

Frequency of worthwhile scavenging opportunities ?

Cordain et al's paper also missed out any mention of how many, or how often, worthwhile scavenging opportunities were encountered. Various studies have suggested average, but not reliable, frequencies of ~9 days, between finding carcasses (or hunting them). So all calculations of a reasonable regular daily intake of DHA for an Early Human family resulting from a single whole scavenged brain would be reduced by nearly 90%. 

see The Skull & Bones Club

3

Considering only two very extreme diets leaves any observations or findings open to extreme doubt:

Cordain et al's paper considers only two extremes:

Brain tissue and bone marrow  vs African lake fish

and concludes that fish are too energy-poor to be worth considering. 

As well as DHA, energy is also required for Early Human brain development.

Cordain's group recognised that a rich source of energy was also required for brain development, while Crawford's didn't.

Energy rich food, as well as AA and DHA, is absolutely essential for a developing foetal and infant brain, via the mother's placenta, breast milk, or later, after weaning, directly. 

A new born human baby expends 74% of its energy intake on its brain alone.

But Cordain's papers omit any mention of other energy-rich foods that omnivorous Early Humans might take along with their brains or their fish, and narrows their options down to bone marrow alone.

Bone marrow, being nearly 85% fat, is certainly a potent source of energy. If you haven't enough energy in your own energy store, take someone else's. But it's no miracle substance, and not the early dietary Philosopher's Stone that so many palaeoanthropologists assume it to be.

And there simply ain't enough around - even if an Early Human found a whole carcass-load of bone marrow every single day, he couldn't have fed his family as well as himself.