by Stuart Quartermaine

Created on: April 15, 2009

Docosahexaenoic acid (DHA) and arachidonic acid (ARA) are both present in large quantities in the grey matter of the human brain, and both accumulate at a rapid rate during the central nervous system growth spurt that takes place shortly before and after birth. Given this, it would be a surprise if these fatty acids did not boost the brain in some respect. However, there are several reasons to be wary of the way in which this inferred relationship is popularly portrayed, and several clarifications that need to be made.

DHA is one of many omega-3 fatty acids. Alpha-linolenic acid (ALA) is referred to as the "parent" of the omega-3 family because it is the precursor to eicosapentaenoic acid (EPA), which is the precursor to docosapentaenoic acid (DPA), which is the precursor to DHA. Linoleic acid (LA) is referred to as the "parent" of the omega-6 family because it is the precursor to gamma-linolenic acid (GLA), which is the precursor to ARA. As a result, it is sometimes assumed that consuming generous quantities of ALA (e.g. from flax seeds or walnuts) and LA (e.g. from walnuts and most seeds and vegetable oils) will have a beneficial effect on the brain.

Often the emphasis is placed entirely on "omega-3", with all types and sources of omega-3 being deemed equally worthy, and all persons of all ages being portrayed as beneficiaries. Since the inherently "good" and "healthy" status of omega-3s is seen to be self-evident, it is further assumed that their goodness is dose-responsive and that brains will get bigger and moods better (both without limit in space or time) as more seafood is eaten and as more flax oil is poured over more grass-fed meat and more green vegetables. So single-minded is the focus on the putative benefits of omega-3s that the potential positive or negative impact of any other food, nutrient, lifestyle or socio-economic factor is completely disregarded.

In reality, the conversion rate of ALA into DHA in humans is barely higher than zero. Supplementing with generous quantities of ALA from flax did result in significantly greater concentrations of EPA and DPA (but not DHA) in the plasma of lactating women, but not in greater concentrations of any of them in the breast milk (where DHA was most needed). There was a "trend" for EPA (only present in minute quantities in the brain) to increase in breast milk, but it looks like there was also a trend for the trendiness of this trend to become less trendy each week. (The conversion of LA into GLA and ARA

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