There is a large body of evidence suggesting that omega-3 fatty acids play a key role in supporting cognitive processes (1). They are considered an essential type of fat (2). Omega-3 fatty acids are necessary for human health, but the body can’t make them, which means they have to be sourced from one’s diet. Most other types of fat can be made from other fats or raw materials (3).
Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is a primary structural component of the human brain. It is the most abundant omega-3 fatty acid in cell membranes in the brain. Therefore, without a sufficient intake of dietary omega-3, brain function will suffer.
Sources of DHA
You can get your intake of DHA from cold-water, fatty fish, such as salmon, tuna (bluefin tuna have up to five times more DHA than other types of tuna), sardines, shellfish and herring (4). Fish also contains EPA – another essential omega-3 fatty acid that can improve cognitive function (5). Fish oil capsules are another source of both DHA and EPA.
So what about vegetarians and vegans? DHA and EPA can be sourced from algae (6). But other than algae, there are no vegan sources of DHA and EPA. However, other plant-based foods do contain omega-3 fatty acids, which is then converted into DHA and EPA.
It’s worth noting, however, that omega-6 (also essential) inhibits the conversion of omega-3 into DHA and EPA (7). So while walnuts and sesame seeds are an excellent source of omega-3, they contain much higher amounts of omega-6. So getting an adequate source of DHA and EPA isn’t as easy as just eating foods high in omega-3. And low intake of omega-3 isn’t just an issue for vegetarians and vegans. One report found that Americans are consuming 10-20 times more omega-6 than omega-3 (8).
Plant-based sources of omega-3, with low omega-3 to omega-6 ratios include flax seeds, chia seeds, hemp seeds, mustard oil, sprulina (a naturally occurring algae), beans, winter squash, leafy greens, cabbage, berries, wild rice, mangoes and honeydew melon (9).
The role of diet in human evolution
It has been proposed that access to DHA during human evolution played a key role in increasing the brain/body-mass ratio. The fact that DHA is an important brain constituent supports the idea that consuming fish (10) (so a diet high in DHA) was necessary for the doubling of our brain size (11). Indeed, evidence shows that early hominids adapted to consuming fish and thus gained access to DHA before this explosion in brain size (12).
Dr Michael Crawford believes that the brain dramatically increased in size 6 million years ago, not because apes came out of the trees to hunt on the savannah, but because they arrived at the coast and found supplies of fish (13). However, there are some issues with this interpretation of human evolution. Firstly, 6 million years ago brain size increased only slightly (14). The real jump was 2 million years ago to the present day – the doubling of brain size. Also, humanity’s ancestors did not seem to be exclusively coastal. But however our evolution played out, if we lack DHA in our diets today, we suffer – and in many ways.
Being an optimal human
There is a body of evidence linking omega-3 deficiencies to aggression and violent behaviour (15). A US study also found that supplementation of omega-3 fatty acids reduced anger and aggression in those with histories of violence (16). Joseph Hibbeln, who was in charge of the study, notes that most western countries consume more omega-6 than ever before, which as we’ve seen earlier, blocks the conversion of omega-3 into DHA and EPA.
Hibbeln also highlights a correlation between high omega-6 consumption and low omega-3 consumption, and an increase in murder rates. However, this doesn’t prove that one causes the other. There could be many other factors contributing to an increase in murder rates. Nevertheless, Hibbeln points out that some of the trends you think would lead to more violence – increased availability of guns and alcohol, or urbanisation – don’t actually seem to do so.
Omega-3 fatty acids have also been shown to be effective in the treatment of depression (17). Other research suggests that omega-3 deficiency is linked to depression (18, 19). This latter study seems to explain the findings of the former.
While it may seem obvious that we should eat more fish in light of this evidence, our oceans are subject to overfishing (20). It is not sustainable. So we may need to make the most of biotechnology, by genetically modifying crops so that they have higher levels of omega-3.
About the author: Sam Woolfe @samwoolfe
I’m currently a Writer at The Canary, covering issues relating to the food industry, drugs, health, well-being and nutrition. I’m also a Blogger for Inspiring Interns, where I offer careers advice for graduates. If you have a story you want me to cover, drop me a message on Twitter (@samwoolfe). You can also check out my travel blog (samreflectsontravel.com) and personal blog (www.samwoolfe.com) to read my articles on philosophy, psychology, and more opinion-related content.
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2805706/ in humans