Your brain needs food too

Background

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). 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 capsules 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 show 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 read more