To test the hypothesis, Hibbeln and his colleagues have mapped the growth in consumption of omega-6 fatty acids from seed oils in 38 countries since the
1960s against the rise in murder rates over the same period. In all cases there is an unnerving match. As omega-6 goes up, so do homicides in a linear
progression. Industrial societies where omega-3 consumption has remained high and omega-6 low because people eat fish, such as Japan, have low rates
of murder and depression.
Of course, all these graphs prove is that there is a striking correlation between violence and omega 6-fatty acids in the diet. They don't prove that high omega-6
and low omega-3 fat consumption actually causes violence. Moreover, many other things have changed in the last century and been blamed for rising violence
- exposure to violence in the media, the breakdown of the family unit and increased consumption of sugar, to take a few examples. But some of the trends you
might expect to be linked to increased violence - such as availability of firearms and alcohol, or urbanisation - do not in fact reliably predict a rise in murder
across countries, according to Hibbeln.
There has been a backlash recently against the hype surrounding omega-3 in the UK from scientists arguing that the evidence remains sketchy. Part of the
backlash stems from the eagerness of some supplement companies to suggest that fish oils work might wonders even on children who have no behavioural
problems.
Alan Johnson, the education secretary, appeared to be jumping on the bandwagon recently when he floated the idea of giving fish oils to all school children.
The idea was quickly knocked down when the food standards agency published a review of the evidence on the effect of nutrition on learning among
schoolchildren and concluded there was not enough to conclude much, partly because very few scientific trials have been done.
Professor John Stein, of the department of physiology at Oxford University, where much of the UK research on omega-3 fatty acid deficiencies has been based,
agrees: "There is only slender evidence that children with no particular problem would benefit from fish oil. And I would always say [for the general population]
it's better to get omega-3 fatty acids by eating fish, which carries all the vitamins and minerals needed to metabolise them."
However, he believes that the evidence from the UK prison study and from Hibbeln's research in the US on the link between nutritional deficiency and crime is "
strong", although the mechanisms involved are still not fully understood.
Hibbeln, Stein and others have been investigating what the mechanisms of a causal relationship between diet and aggression might be. This is where the
biochemistry and biophysics comes in.
Essential fatty acids are called essential because humans cannot make them but must obtain them from the diet. The brain is a fatty organ - it's 60% fat by dry
weight, and the essential fatty acids are what make part of its structure, making up 20% of the nerve cells' membranes. The synapses, or junctions where
nerve cells connect with other nerve cells, contain even higher concentrations of essential fatty acids - being made of about 60% of the omega-3 fatty acid DHA.
Communication between the nerve cells depends on neurotransmitters, such as serotonin and dopamine, docking with receptors in the nerve cell membrane.
Omega-3 DHA is very long and highly flexible. When it is incorporated into the nerve cell membrane it helps make the membrane itself elastic and fluid so that
signals pass through it efficiently. But if the wrong fatty acids are incorporated into the membrane, the neurotransmitters can't dock properly. We know from
many other studies what happens when the neurotransmitter systems don't work efficiently. Low serotonin levels are known to predict an increased risk of
suicide, depression and violent and impulsive behaviour. And dopamine is what controls the reward processes in the brain.
Laboratory tests at NIH have shown that the composition of tissue and in particular of the nerve cell membrane of people in the US is different from that of the
Japanese, who eat a diet rich in omega-3 fatty acids from fish. Americans have cell membranes higher in the less flexible omega-6 fatty acids, which appear to
have displaced the elastic omega-3 fatty acids found in Japanese nerve cells.
Hibbeln's theory is that because the omega-6 fatty acids compete with the omega-3 fatty acids for the same metabolic pathways, when omega-6 dominates in
the diet, we can't convert the omega-3s to DHA and EPA, the longer chain versions we need for the brain. What seems to happen then is that the brain picks up
a more rigid omega-6 fatty acid DPA instead of DHA to build the cell membranes - and they don't function so well.
Other experts blame the trans fats produced by partial hydrogenation of industrial oils for processed foods. Trans fats have been shown to interfere with the
synthesis of essentials fats in foetuses and infants. Minerals such as zinc and the B vitamins are needed to metabolise essential fats, so deficiencies in these
may be playing an important part too.
There is also evidence that deficiencies in DHA/EPA at times when the brain is developing rapidly - in the womb, in the first 5 years of life and at puberty - can
affect its architecture permanently. Animal studies have shown that those deprived of omega-3 fatty acids over two generations have offspring who cannot
release dopamine and serotonin so effectively.
"The extension of all this is that if children are left with low dopamine as a result of early deficits in their own or their mother's diets, they cannot experience
reward in the same way and they cannot learn from reward and punishment. If their serotonin levels are low, they cannot inhibit their impulses or regulate their
emotional responses," Hibbeln points out.
Mental health
Here too you have one possible factor in cycles of deprivation (again, no one is suggesting diet is the only factor) and why criminal behaviour is apparently
higher among lower socio-economic groups where nutrition is likely to be poorer.
These effects of the industrialisation of the diet on the brain were also predicted in the 1970s by a leading fats expert in the UK, Professor Michael Crawford,
now at London's Metropolitan University. He established that DHA was structural to the brain and foresaw that deficiencies would lead to a surge in mental
health and behavioural problems - a prediction borne out by the UK's mental health figures.
It was two decades later before the first study of the effect of diet on behaviour took place in a UK prison. Bernard Gesch, now a senior researcher at Stein's
Oxford laboratory, first became involved with nutrition and its relationship to crime as a director of the charity Natural Justice in northwest England. He was
supervising persistent offenders in the community and was struck by their diets. He later set out to test the idea that poor diet might cause antisocial behaviour
and crime in the maximum security Aylesbury prison.
His study, a placebo-controlled double blind randomised trial, took 231 volunteer prisoners and assigned half to a regime of multivitamin, mineral and
essential fatty acid supplements and half to placebos. The supplement aimed to bring the prisoners' intakes of nutrients up to the level recommended by
government. It was not specifically a fatty acid trial, and Gesch points out that nutrition is not pharmacology but involves complex interactions of many nutrients.
Prison trial.
(continued here) BACK
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medicine, but will interest his patients in
the care of the human body, in diet, and in
the cause and prevention of disease."
Thomas Edison
