Understanding the Brain on Omegas 3 and 6

The human brain is about 60% fat. Omega-6 fats comprise <2% of the total brain fatty acids and, hence, are considered as non-functional. Whereas saturated and omega-3 fats make up over 84% of the total brain fatty acids - and they are mandatory for proper brain functions and development.

Imbalanced Omegas Ratio

Yet the intake of linoleic acid, the most common form of omega-6, has risen from 1–2% (before the 1930s) to 7% (as of 2000) of daily calories - mainly from soybean oil which is typically found in processed foods.

Whereas the consumption of omega-3 fats, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has remained stable at <1% of daily calories. Oily fish and seafood have the highest abundance of EPA and DHA, followed by pasture-raised beef and eggs.

As follows, the ratio of omega-6:omega-3 has shifted from 4:1 to the present 20:1 (or even higher). This out-of-whack ratio is deemed harmful because the biochemical pathways of omega-6 fats counteract the anti-inflammatory benefits of omega-3 fats.

As Korean researchers explain in Life Sciences, "owing to competing roles of [omega 3 and 6] in the production of anti-inflammatory and inflammatory eicosanoids, a balanced intake of [omegas] is necessary to evade chronic diseases and to maintain good health."

That's why the Western diet with an imbalanced omegas ratio is suggested to be a potent driver of many chronic diseases, such as obesity, rheumatoid arthritis, cancer, and cardiovascular and neurodegenerative diseases.

Part I: The Brain on Omega-6

Despite that omega-6 linoleic acid enters the brain at the same rate as other fatty acids, it's not actively integrated into the brain's lipid membranes. About 59% of the linoleic acid is oxidized into metabolic by-products such as carbon dioxide, acetate, and other oxidized linoleic acid metabolites (OXLAMs) that are inflammatory to the brain.

In Rodents

Studies have shown that reducing linoleic acid from 5.2% to 0.4% of daily calories leads to a better brain inflammatory profile. Rodents fed with a diet rich in linoleic acid, in turn, had increased levels of OXLAMs and inflammation in their brains.

In Human Adults

Researchers at the National Institute of Health and the University of North Carolina-Chapel Hill, USA recruited 67 patients with drug-resistant migraines for a randomized controlled trial. While causes of migraines are multifaceted, brain or neuronal inflammation is one of them.

They showed that a modified diet with decreased linoleic acid (from 7% to 2% of daily calories) and increased EPA and DHA (to 1.5g/day) content for 12 weeks alleviated migraines, mental and physical disabilities, and psychological distress to great extents. Lowering linoleic acid alone, however, wasn't enough to produce this clinical improvement.

In Infants and Children

Following the modern rise in omega-6 linoleic acid consumption, its levels in the breastmilk also increased from 7% to 12% of total fatty acids from 1970 to 2000. This 12% content equates to 8% of the infant's daily calorie intake, far exceeding what they need which is 1–2% of linoleic acid.

Epidemiological studies have reported that high linoleic acid content in the maternal diet and breastmilk are associated with poor neurodevelopmental outcomes - such as lower cognitive abilities and motor coordination - in infants and children. These findings are also independent of the DHA content of breast milk. Ameer Taha, assistant professor at the University of California, therefore says in Nature Science of Food (2020) that this suggests, "A direct impact of excess breast milk linoleic acid (and hence maternal intake) on brain development."

To Summarize

"When present in excess and chronically, [linoleic acid] induces ataxia in chickens, promotes neuroinflammation in rats and is linked to abnormal neurodevelopment in humans," Professor Taha sums up. "Excess linoleic acid in the food supply might adversely affect the brain," he asserts.

Lowering linoleic acid intake might, thus, protects the brain against inflammation. As the professor concludes, "the potential benefit of linoleic acid-lowering merits detailed evaluation … clinical studies, to test whether this translates into tangible reductions in the risk of neurodegenerative disorders and neurodevelopmental abnormalities at a population level."

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Part II: The Brain on Omega-3

DHA alone makes up 40% of the total brain fatty acids. In contrast, EPA is about 250–300 times lower than DHA in the brain and plays more important anti-inflammatory roles in other organs. In this way, EPA indirectly benefits the brain - by lowering systemic inflammation for a healthier brain function, for example.

"A hypothesis for the indispensable nature of DHA suggests that the unique structure of DHA allows for the quantum transfer and communication of π-electrons across the membrane," writes Simon Dyall who specializes in omega-3 neuroprotection research. "This [explains] the precise depolarization of retinal membranes and the cohesive, organized neural signaling essential for higher intelligence."

In other words, DHA enables the efficient signalling between neurons, allowing for complex brain processes such as intelligence.

In Rodents

Feeding rodents a diet deficient in omega-3 fats is known to induce severe abnormalities in neurotransmitter signaling and brain and neuronal structure. These omega-3 deficient rodents develop neuropsychiatric disorders, such as depression and learning deficits, as a result.

In Human Adults

Autopsies revealed a lower DHA content in the brain of victims of Alzheimer's disease, compared to cognitively healthy individuals. Further, the lower the DHA content, the worse their cognitive decline was.

That's why adequate levels of EPA and DHA are protective factors against brain aging. Increased circulating levels of EPA and DHA are associated with a lower risk (and severity) of cognitive decline, dementia, depression and brain shrinkage.

Likewise, frequent consumption of fatty fish or supplements containing EPA and DHA minimize those risks. Some clinical trials even showed that they improve or delay the symptoms of neurodegenerative diseases. But these studies involve people who are likely deficient in omega-3.

There're, however, conflicting findings showing no significant clinical improvement. This indicates that causes of neurodegeneration are always multifaceted, as reviewed in a 2019 paper. To give an example, the authors wrote, "adequate B vitamin status is required to obtain beneficial effects of omega-3 on cognitive performance." This means that omega-3 fats might not benefit those whose diet is deficient in vitamin B.

In Infants and Children

Dietary DHA is actively incorporated into the infant's brain during the third trimester of pregnancy and up to age 2. And DHA levels are maintained thereafter. Sufficient DHA in maternal diet and breastmilk is, thus, crucial for the growing baby brain.

In infants whose source of breast milk is only 0.17% DHA, they developed lower visual clarity and language maturity during the first 14 months of age, compared to infants who drank 0.34% DHA breast milk. Many other studies have investigated the link between DHA and brain development. Reviewing these studies led to Sheila Innin, a professor of pediatrics at the University of British Colombia, to conclude that, "A consistent pattern emerges in which the maternal or infant circulating levels of DHA at birth is associated with better infant neural and visual development."

But there is no "definite proof that an increase in the early DHA supply improves the mental development of infants," writes Lotte Lauritzen, associate professor of pediatrics and psychology at the University of Copenhagen.

Professor Lauritzen explains that omega-3 supplementation tends to enhance brain function in children with low socioeconomic status and, hence, rarely eat fish and omega-3 fats. To repeat, "The issue is not that taking DHA supplements improves memory - it's that lack of DHA worsens memory [across all age groups]."

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Key Points for Omega-6

In adults, reducing omega-6 intake can be beneficial for brain health. But increasing omega-3 might still be needed to complement this effect (recall the migraine study).

In infants and children, excessive omega-6 alone (independent of DHA) might harm their brain development (recall Professor Taha's words).

Whether to reduce omega-6 consumption for brain health is still debatable (no robust clinical trials yet).

But considering the present imbalanced omegas ratio, lowering omega-6 might do more good than harm -as it lets omega-3 does its job.

The main source of omega-6 in the food supply is soybean oil (recall the statistics figure), which is often found in processed and fast foods.

Key Points for Omega-3

The brain (young or old) thrives on omega-3, particularly DHA. Without it, the brain ages and degenerates more easily and quickly.

It's important to not deprive the brain of DHA by increasing omega-3 intake (and perhaps also lowering omega-6).

Increasing omega-3 intake might boost cognition, but only in those whose brains are 'aging' from DHA deficiencies (and whose vitamin B levels are adequate).

How much omega-3 to eat? While there're no precise numbers as it depends on pre-existing nutritional deficiencies and the bioavailability of the food source, more is recommended considering the excessive omega-6 in the present food supply.