The link between dietary fat and its role in brain function is nowhere more evident than in epilepsy. Epilepsy is a brain disorder, and the ketogenic diet is a well-established treatment for the condition.

Studies have found that half of affected children experience at least 50% reduction in seizures after 6 months on the ketogenic diet, and one third achieve over 90% reduction. Indeed, research has found that it is a form of therapy that can, in some cases, “completely remove the need for medication”.

The ketogenic diet used to be the treatment of choice (if not the only treatment) for severe childhood epilepsy in the 1920s. Then, with the introduction of anticonvulsant medications in the 1930s, the use of the diet all but disappeared. It re-emerged in the 1990s with the publication of new scientific research.

If the ketogenic diet works for epilepsy, why not for other brain disorders? Preliminary studies suggest that what’s good for the goose, is good for the gander.

“The ketogenic diet (KD) is now a proven therapy for drug-resistant epilepsy supporting its use in multiple neurological disease states.” (Stafstrom & Rho 2012).

As well as needing fat for fuel, a baby’s brain requires specific fat for normal cognitive development and intellectual skills. Without that specific fat, there is the serious risk of developing brain dysfunction.

There are two fats that are essential for optimal brain function in the developing foetus and the newborn baby: the omega-3 fatty acid DHA (docosahexaenoic acid) and the omega-6 fatty acid ARA (arachidonic acid).

Both these fats form part of each cell membrane, and control what passes in and out of each nerve cell. They help develop the central nervous system. They are involved in communication between nerve cells, the firing of neurons, the regulation of neurotransmitters and the development of cognitive skills.

Surf and turf

DHA and ARA are polyunsaturated fats that are found pre-formed in animal-source foods only. The main dietary source of DHA is fish and seafood, and the main dietary source of ARA is meat.

DHA is found abundantly in seafood and oily fish, including salmon, mackerel, trout, herring and anchovy. Meat contains only small amounts of DHA, though offal — especially brain — is a great source, albeit not a terribly popular one.

ARA is found largely in meat, but some can be obtained from sea and fresh water foods. The best sources of ARA are beef, poultry, seafood and eggs.

Nuts and seeds and other plant foods are often suggested as a suitable vegetarian source of omega-3 fats. That is not the case. Although it is true that the body can make some limited DHA (and EPA, its precursor) from plant sources, its ability to do so is poor, and effectively meaningless. The liver converts less than 0.5% of the omega-3 fat in plant sources to DHA. That’s on a good day: in many studies, that conversion rate has been shown to be less than 0.1%, making it “negligible”.

“Thus, the developing human brain unequivocally needs to be provided with pre-formed DHA or it will not be able to optimally accumulate DHA.” (Cunnane & Crawford 2014)

The same goes for ARA, which too is abundant in the brain. ARA is structurally similar to DHA, and is a significant component of the cell membrane, though they are metabolically and functionally distinct. One cannot replace the other.

Like DHA, pre-formed ARA is unique to animal-source foods, and conversion of omega-6 fats in plant foods to ARA is very low and unreliable.

“The synthesis of DHA and ARA is limited in infants and both DHA and ARA must be obtained from dietary sources.” (Hadley et al 2016)

What happens without enough of these two fatty acids?

Only two mammalian species have disproportionately large brains and advanced cognition — humans and bottlenose dolphins. Both depend on DHA for that cognition.

Children who lack DHA are more likely to have increased rates of neurological disorders, in particular attention deficit hyperactivity disorder (ADHD), and autism.

“It is our contention that the movement in the 19th to 21st centuries away from traditional use of sea foods and increased emphasis on land based food supply is a likely cause in the rise in brain disorders including mental ill-health, stress, and other psychiatric disorders.”(Crawford et al 2014).

Today, ADHD is the most frequently diagnosed neuro-behavioural disorder of childhood, and it is becoming increasingly prevalent. In 2014, the Centers for Disease Control and Prevention confirmed that there had been a 42% increase in the number of children diagnosed with the condition since 2006. In America today, 11% of children aged 4 to 17 live with ADHD.

There is a growing body of evidence to suggest that ADHD may be preceded by low DHA in the womb.

The link between dietary fat and autism is also strong, and low levels of both DHA and ARA have been found in children on the autistic spectrum. In a study published in 2015 in International Journal of Molecular Sciences, the fatty acid profile of 121 autistic children, aged 3–7, was analysed and compared with children without the condition. The autistic children were found to have levels of ARA and DHA that were “particularly decreased”, compared to the non-autistic controls.