Why is docosahexanoic acid (DHA), a long-chain (22 carbons), polyunsaturated (6 unsaturated double bonds), omega-3 fatty acid essential for the photoreceptors in our eyes and for the synapses (gaps) between neurons in our brains? DHA is fragile, easily oxidized, and exceedingly difficult to obtain in a land-based area. It is abundant in the oceans and in lakes. DHA is essential for the brains and eyes of all animals. Those who have developed and grown larger on the land, for example, in the African savannah, show progressively smaller percentages of brain-to-body size and some have even lost brain size absolutely. A tiny monkey, weighing less than one kilogram (kg), "has 2.3% of its body weight as brain, a 60 kg chimpanzee 0.5%. The larger gorilla at 110 kg has only 0.25% brain, which is physically smaller than the chimpanzee's brain."

. . . Homo sapiens with our amazingly large brain-to-body size must have developed at the water-land interface. They point out that the abundant nutrients are needed over generations and are especially vital for fetal development. "In coastal hunter-gatherer cultures, women are responsible for collecting shellfish. So, stone age women could have easily provided themselves with a plentiful source of brain-specific nutrition, even when strength/mobility are compromised during pregnancy and lactation."

All these examples point to the need for both the DHA and the long-chain omega-6 fatty acid, arachidonic, which has a 20-carbon chain with 4 unsaturated double bonds. Arachidonic acid is essential for cardio-vascular development and for mammalian reproduction. For the fetal human brain to grow, an amazing energy supply must be forthcoming. "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 omega-6 fatty acids especially arachidonic acid (AA)." In 42 species so far studied, AA and DHA are major fatty acids needed for the vascular system and for the larger brains of the mammals. When either is absent, development lags or reverses.

Over the millennia both of these long-chain fatty acids and many other essential nutrients have been abundantly available at the sea shore and lake shore. NOHA Honorary Member Michael A. Crawford, PhD, and colleagues contend that Homo sapiens with our amazingly large brain-to-body size must have developed at the water-land interface. They point out that the abundant nutrients are needed over generations and are especially vital for fetal development. "In coastal hunter-gatherer cultures, women are responsible for collecting shellfish. So, stone age women could have easily provided themselves with a plentiful source of brain-specific nutrition, even when strength/mobility are compromised during pregnancy and lactation. Children would have naturally participated in exploitation of, at that time, this extremely rich resource."

The diet in western industrial countries is high in saturated animal fats and heart disease is prevalent. However, we see from the energy and nutrient needs of the human brain that the vascular degeneration that is rampant in western civilization is certainly incompatible with central nervous system expansion. "There is increasing evidence that cardio-vascular disease has its origin in poor fetal nutrition consistent with our hypothesis of long-term, multi-generation effects operating on vascular and central nervous system evolution. These forces can act for expansion or degeneration."

The diet in western industrial countries is high in saturated animal fats and heart disease is prevalent. However, we see from the energy and nutrient needs of the human brain that the vascular degeneration that is rampant in western civilization is certainly incompatible with central nervous system expansion.

Returning to our original question, why is DHA so important? DPA, an omega-3 fatty acid, which is exactly the same as DHA, except that it has one less unsaturated double bond (5 instead of 6), can actually be found abundantly in land-based, savannah animals. Why couldn't all these land-based living creatures use DPA for the development of their brains? Professor Crawford and his colleagues have some interesting speculations. They have studied the structures of the two molecules, using computer simulations, both of the molecules themselves and also as they could be incorporated into cell membranes. An even more intriguing difference involves the speculation that there may be differences in the electrical properties of the two molecules. DHA with its six double bonds has an interesting symmetry, which is lacking in DPA. They propose developing further experiments.
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* Crawford, M.A., et al, "Evidence for the unique function of DHA during the evolution of the modern hominid brain," Lipids, 34:S39-S47, 1999.

Article from NOHA NEWS, Vol. XXVIII, No. 4, Fall 2003, page 6.