*Geek Box: ALA and DHA as EFAs

*Geek Box: ALA and DHA as Essential Fatty Acids

Up to 60% of the brain’s dry weight is comprised of fat, of which up to 30% is comprised of polyunsaturated essential fatty acids [EFAs]. In particular, DHA comprises over 90% of omega-3 fatty acids in the brain, while both EPA and [ALA are low in brain tissue, comprising less than 1% of total brain fatty acid composition.

The critical role of DHA in neural growth and development suggests an important evolutionary requirement for this long-chain omega-3.This predominant role of DHA in the brain has generated a “shore-based perspective” of human evolution. Anthropological evidence for the expansion of humans from the African rift valley suggests that migration along coastal and inland watercourses provided access to both marine and freshwater sources of fish, and in particular long-chain omega-3 fatty acids. Stable isotope analysis of bones of early Sapiens have indicated that marine protein sources constituted significant proportions of daily energy in the human diet.

The evidence suggests that consistent access to such food sources over multiple generations coincided with the period of exponential encephalisation [the growth of the brain], preceding the rapid development of language, complex reasoning, and problem solving cognitive capacities associated with the prefrontal cortex. Relative to other mammalian species, and indeed our primate cousins, the human brain is disproportionately large compared to body size.

A number of lines of nutritional evidence support the anthropological research. First, other mammals with high levels of other polyunsaturated fats in membranes, but without a direct dietary source of preformed DHA, did not develop large brains, indicating a foundational need for preformed DHA in the early modern human diet.

Secondly, humans lost the full activity of the delta-6-desaturase enzyme responsible for converting ALA to EPA and ultimately to DHA. While it is highly active in neonatal periods, in adulthood there is very little conversion of ALA through to DHA, which again suggests a direct source of preformed DHA as a foundational dietary characteristic associated with human encephalisation. Anthropological theory also suggests that fish would have been a far less risky prey for humans to hunt, and that the cost of obtaining land mammals as prey may have been quite high.

However, only ALA is considered an essential fatty acid, due to the fact that humans lack the necessary enzyme to produce ALA in the body, therefore requiring a direct dietary source. Conversely, technically DHA may be synthesised from ALA, notwithstanding that this conversion is very low. A number of researchers in this area therefore consider DHA to be essential, due to the requirement for a preformed source of DHA to maintain brain concentrations. There remain many gaps in our knowledge, however, and this area is likely to be one of contention as the frankly boring argument about whether nutrients of primarily animal source have a place in the modern human diet continues. If this topic is of interest to you, see references 3-5.