Fish has always been thought of as ‘brain food’ and it is recommended that we eat at least two portions of fish a week, one of which should be ‘oily’. All forms of seafood are rich in the vitamins and minerals vital for brain function, but it is oily fish (for example salmon, mackerel, tuna, herring, and trout) that are particularly important as they contain omega-3 polyunsaturated fatty acids (PUFAs) – Note for vegetarians and vegans: taking refined algae oil does essentially the same job; the fish eat the algae and that’s where they get their omega-3s from.
It is important to clarify that there are two distinct classes of PUFA; omega-3 and omega-6. These two classes have different actions in the body and in mammals there is no conversion of one class to the other. In Westernised diets, linoleic acid (an omega-6 found in many vegetable oils, meat, dairy, and eggs) is the most common PUFA consumed, followed by a-linolenic acid (an omega-3 found in flax, chia and hemp seeds as well as walnuts and rapeseed oil). In the liver, the same enzymatic process converts these dietary sources to forms used by the body; linoleic acid is primarily converted to arachidonic acid (AA) and a-linolenic acid is first converted to eicosapentaenoic acid (EPA) then a proportion is converted to docosahexaenoic acid (DHA).
Oily fish contain pre-formed EPA and DHA without the need for any conversion process by the body. This is important because the conversion of a-linolenic acid to EPA and DHA is very inefficient (~6% to EPA and ~ 3.8% to DHA), and where the diet is rich in omega-6 PUFAs this conversion is reduced by a further 40–50% due to competition for enzymes in the conversion process.
Why is this distinction important? Put simply omega-3 PUFAs have anti-inflammatory actions whereas omega-6s have pro-inflammatory actions within the body. It is thought that humans evolved eating a ratio of omega-6 to omega-3 PUFAs between 2–4:1; current Westernised diets are estimated to be in the region of 15–20:1, a huge imbalance. Much of this change has occurred over the last 150 years as a result of the improved ease of vegetable oil production and a move away from the use of animal fats in cooking. In addition to this, the move to more intensive farming of meat and fish fed on grain-based feeds has reduced levels of omega-3 in these foods. It is thought that the omega-6/omega-3 imbalance contributes to many conditions that involve an inflammatory response including cardiovascular disease, cancers, and autoimmune diseases. What needs to be remembered is that omega-6 fatty acids are not in essence bad, it’s just that omega-3 fatty acids have health benefits that omega-6s don’t. In addition, over consumption of omega-6 get in the way of getting the most out of the omega-3s we do eat, potentially having negative consequences for health.
How do omega-3 fatty acids benefit brain function? The brain is 60% lipid (fat; dry weight), mainly from the phospholipid composition of cellular membranes. DHA makes up to 50% of membrane composition in brain tissues, including composition of cell walls and organelle structures. Strength and integrity of membranes has knock on effects on signal transmission and mitochondrial function (energy production in the cell). In addition, EPA and DHA are involved in production and maintenance of myelin, the substance that forms a fatty insulator around axons meaning that signal transmission is more efficient. It is the loss of myelin in multiple sclerosis that causes the problems associated with this disease. Following brain injury, either from an accident or stroke, omega-3s have the potential to reduce some of the harmful processes following the damage including problems with mitochondrial function, excessive inflammation, damage to the neurons, and cell death. In addition, it has been shown that giving EPA to patients after a sub-arachnoid haemorrhage (a form of stroke) results in an improved outcome for these patients. It has even been suggested that having a diet rich in omega-3 fatty acids is neuroprotective against dementia.
As with all things nutrition-related it is better to get your omega-3 from food; from wild cold water, oily fish for EPA and DHA in the form ready for use in the body and from the nuts, seeds and olive oil that contain ALA. In addition, it is important to think about reducing the amount of omega-6 fats in the diet to ensure that the best use can be made of the omega-3s we are eating.
This article is for informational purposes only and is not intended to be a substitute for professional advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a psychological or psychiatric condition. Never disregard professional medical advice or delay seeking it because of something you have read online. Read the full disclaimer here.
Rebecca Denniss is Associate Lecturer at Sheffield Hallam University. Her current research focus is to improve the long-term cognitive outcomes for individuals sustaining traumatic brain injuries, whether it is through better understanding of brain changes, improved rehabilitation strategies or micronutrient interventions. More broadly, she is interested in neurodegenerative processes and associated cognitive deficits. Follow her on twitter @Neuro_Ceutical