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For many years, the conventional wisdom has been that the composition and functioning of the brain is not something that can be altered by diet. This section will challenge that view, and outline the evidence that diet can alter brain composition and brain function. The implications of this work are very profound, and have a bearing on conditions such as aggression, depression, anti-social behaviour, road rage and hyperactivity in children. All are increasingly frequent features of life at the end of the 20th century. The evidence suggests that a relatively small change in diet could improve these conditions.


The human brain is unique within the animal world in that it forms a greater proportion of our body weight than in other species. It is also unique in that the process of formation is largely complete shortly after birth. The cells present get larger, but new cells are not formed. The brain is also unique in its composition. Of the solid (non-water) matter in the brain, 60% is fat, or lipid, and of that, polyunsaturates form the biggest component (Crawford,M., et al, 1992). Two polyunsaturates dominate, the omega-6 20 carbon polyunsaturate arachidonic acid (AA), and the omega-3 22 carbon polyunsaturate docosahexaenoic acid (DHA). Arachidonic acid can be made in the body from the linoleic acid in vegetable oils, with small amounts of the preformed AA present in eggs and meat. Fish is the only significant dietary source of the long chain omega-3 polyunsaturate DHA. Breast milk provides both.

Brain Composition and Diet

Studies of many different animal species have shown that the long chain polyunsaturates are present to a much greater extent in brain than in other animal tissue(Bourre,J.M., et al, 1991).

The first thoughts that diet might influence brain composition followed animal studies using diets devoid of omega-3 polyunsaturates. Rats reared for several generations on such diets showed changes in brain composition, with fewer omega-3 polyunsaturates, and more of the vegetable-derived omega-6 polyunsaturates. The omega-3 deficient rats also performed poorly in learning tests (Lamptey,M.S., & Walker,B.L.,1976).

Monkey.wmf (23054 bytes)Neuringer (1986) showed in rhesus monkeys that brain omega-3 levels could be reduced by feeding omega-3 deficient diets, and that their behaviour was changed. The monkeys exhibited polydipsia, (they drank more water, and voided more urine), and their behaviour was described as more restless, less settled. (Reisbeck et al, 1994)

Studies with human brains are more difficult to carry out. A post mortem study of brain composition in infants has shown that babies reared on breast-milk (which contains long chain omega-3 & omega-6 poly-unsaturates) had detectable amounts of AA and DHA present, while those reared on formula feeds (which at the time were devoid of long chain polyunsaturates) did not (Farquharson et al, 1995). Makrides et al (1994) also examined post-mortem samples from infants, and looked at brain, blood (erythrocyte) and retina samples. Formula-fed infants showed significantly less DHA in the erythrocyte and brain samples compared to breast-fed infants. Retinal samples did not show this difference.

The combination of animal data and infant post-mortem data provides very strong circumstantial evidence that diet does indeed have a subtle but distinct effect on brain composition.

Diet and Brain Function (Behaviour)

The idea that something that is consumed can affect the way we behave is long-established. Alcohol, cannabis and Valium are all well known examples. What is not so well established is the idea that an everyday food substance can affect behaviour. Over the past 30 years we have learned much about the part that the omega-3 polyunsaturates from fish play in heart disease. Recently, several studies have shown that a greater intake of the omega-3’s can bring about (or at least facilitate) desirable changes in brain function.

Omega-3 and Intelligence.

Fish is often credited in folk-lore as being brain food, but it is only in the past 30 years that we have come to recognise the uniquely high concentration of the long chain omega-3’s in brain which makes this true. How the ancients knew this, without modern analytical instruments to help them is impossible to fathom! In 1976 Lamptey & Walker reared rats on omega-3 deficient diets. When given tests of learning ability, the deficient rats performed less well than controls. In humans, evidence of an effect of omega-3 polyunsaturates comes from studies which compare IQ in children who were breast-fed as infants with those fed bottled feeds which at the time were devoid of long chain polyunsaturates.


Several such studies are now in print, (Lanting et al, 1994, Horwood and Fergusson,1998) showing an approximately 3 point difference in IQ when measured in childhood years. More recently, Willatts et al (1998) from Dundee University in Scotland have shown that having long chain omega-3 polyunsaturates in infant formulae enables the recipients to solve problems more rapidly than comparable infants raised on standard formulae.


Omega-3 and Aggression

The evidence comes from two studies carried out in Japan, where final year medical students were used in a double blind study. Hamazaki et al (1996) gave the students either fish oil capsules with a high DHA content, or placebo cBoxer1.wmf (16186 bytes)apsules everyday for three months. At times during the trial the student’s feelings of aggression and hostility towards others was assessed. The end of the trial co-incided with final exams, a highly stressful period. The students on placebo capsules started to showed increased aggression and hostility to each other as the exams approached, while the students receiving the DHA supplements remained calm. When this experiment was repeated at a time when external stress (i.e. exams) was absent, there was no measurable effect of the DHA (Hamazaki et al, 1998).

Omega-3 and Depression

Epidemiological studies have shown that where fish eating is common, depression is uncommon, and vice-versa (Hibbeln and Salem, 1995). Other studies have shown that the levels of the long chain omega-3’s in blood of depressed people are lower in those with more severe depression. (Adams et al, 1996, Maes et al, 1996). Detailed investigations have suggested that the long chain omega-3’s are important in regulating the re-uptake of a brain chemical called serotonin (Hibbeln et al, 1998). The well-known anti-depressant Prozac also works by influencing this process. Hence the idea that fish oils might be Nature’s Prozac!

To date only one study has reported results on the use of omega-3 supplements in the treatment of depression. That study   was by Dr Andrew Stoll (1999) from McLean Hospital in Belmont, Massachusetts. He  treated severely depressed, suicidal patients (so severe that they were being treated in hospital) with heroic doses of  fish oil  (9g/day of omega-3, equivalent to about 25g of fish oil). After 4 months of treatment, the benefits to the treated patients was so great, that the trial was stopped prematurely, on the grounds that it would have been unethical to deny the placebo group the benefits of the fish oil.

Omega-3 and Schizophrenia

The subject of schizophrenia has been much in the news of late, because of Care in the Community and the brutal murders in motiveless attacks by uncontrolled schizophrenics. The relevance of this to studies on omega-3 is that some schizophrenics have low blood levels of the omega-3 polyunsaturates (Edwards et al, 1998). Laugharne et al (1996) showed by adding fish oil to the diet of schizophrenics in an open trial that symptoms are reduced, both the so-called negative, or depressive symptoms which result in apathy and unco-operative behaviour , and the positive symptoms, which can lead to hallucinations and aggression. This work has now been successfully repeated in a double blind trial (Peet,M., Personal Communication, 1998). Whether the low blood omega-3 levels are a result of a dietary deficiency, or some metabolic abnormality is not yet known, though one study has shown that schizophrenics are less likely to have been breast-fed, and hence less likely to have started life with a good supply of DHA.

Omega-3 and ADHD

Monkeys reared on omega-3 deficient diets exhibited restless and unsettled behaviour. In human terms, this type of behaviour might be considered similar to the hyperactivity that some children exhibit. ADHD, or attention-deficit hyperactivity disorder to give it its proper name is a surprisingly common condition, with something like 3-5% of American and British children affected to some degree. Symptoms range from difficulty in concentrating, to fidgeting, restlessness, impulsiveness and general naughtiness, to antisocial behaviour and violent aggression towards others. The problem often comes with other symptoms related to disorders of fatty acid metabolism, such as excessive thirst, skin problems, sleep difficulties, dyslexia (vision disturbances) and dyspraxia (poor co-ordination and clumsiness). Sufferers have recently been shown to have low blood levels of long chain omega-3 polyunsaturates, (Stevens et al, 1995,) with lower levels in those with the most severe symptoms (Stevens, et al 1996). Supplementation trials are underway, some of which are showing encouraging results, (Richardson,1998, personal communication) though as yet, full details have not appeared in print.

The diet connection.

Most of the conditions referred to have more than one causative factor, and the impact of the amount and type of polyunsaturate in the diet will vary from one person to another. One thing all these conditions have in common though is that they are becoming more prevalent in Western industrialised societies. The increase has been especially marked in the past 30 years, and has co-incided with a change in the balance of the polyunsaturates in the diet. The human body needs two types of polyunsaturate to function healthily. It cannot make these from scratch, so they must be supplied in the diet. Hence they are sometime referred to as "essential" fatty acids, or EFAs. There are two families of EFA’s, the omega-6 type, found predominantly in vegetable oils such as sunflowerseed oil, and the omega-3 type, supplied mainly by fish. Both must be supplied in the diet, and the relative amounts of each can have an impact on health. Over the past we have eaten more of the omega-6 polyunsaturates, and less omega-3. The omega-6 increase has come about as a result of recommendations to eat more polyunsaturates to reduce heart disease. Intake of the omega-6 polyunsaturate linoleic acid more than doubled between 1955 and 1995. At the same time, the omega-3 supply dropped, mainly due to a long term fall in fish intake, and in particular a change in the type of fish eaten, with more low-fat, white fish (cod, haddock) being eaten, and less of the oil-rich type such as herring and mackerel.

The overall result has been a change in the balance of the two types of polyunsaturate in the national diet, from an estimated 4:1 ( i.e. 4 parts omega-6,1 part omega-3) in the mid 50’s, to an actual 7:1-8:1 currently. Bear in mind also that these figures are averages, so that within them will be individuals with far more extreme values. Other societies show even more extreme average values that we in Britain do. The American intake is nearer 10:1, while Australians eat a diet which on average provides 12 times more omega-6 than omega-3.

Thus we are now at serious risk of an unbalanced dietary intake of polyunsaturates.

What can be done about it?

We eat too much omega-6, and not enough omega-3. To correct this we must cut down on omega-6 and eat more omega-3. To do this requires a change in the formulation of vegetable oils, margarines and cooking fats generally, away from high omega-6 oils like sunflower and sesame, towards olive and rapeseed (canola)oils. Also required is an increase in the amount of the long chain omega-3 polyunsaturates in the diet. Eating more fish, and in particular more of the oil-rich fish like herring and mackerel, is the best way to do this. Fish eating twice a week should be a minimum goal, as recommended by the Department of Health COMA report in 1994. Special emphasis must be put on encouraging children to eat more fish. Fish oil supplements like good old cod liver oil, or supplements made from fish body oil are another means of increasing omega-3 intake. Foods supplemented with omega-3 can also help.


If we want our caring, tolerant and capable society to survive, we must correct the balance of dietary polyunsaturates, by among others things eating more fish. In addition to the better known cardiovascular benefits of fish, increasing the dietary intake of the long chain omega-3 polyunsaturates will help to improve the mental health and wellbeing of everyone.

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