Also in this week's column:

• Why are some people more attractive to mosquitos?
• What is a Cro-Magnon man?
• How can objects in the same room be different temperatures?

Asked by Tammy Courtland of Boston, Massachusetts

It is no wonder that health authorities usually recommend the eating of two or three servings of fish per week for most people. This is because fatty, cold-water fish contain healthy omega-3 fats (DHA and EPA). Rich sources of these marine omega-3 fats are sardines, salmon, mackerel, and fresh tuna.

There is some evidence to show that poor dietary intakes or low blood levels of these omega-3 fats can result in learning difficulties, behavioral problems, and mental illness. This may indicate a strong relationship between eating fish and brain development.

Sixty per cent of the brain is composed of fat - but not just any fat. DHA and EPA are good fats. DHA (docosahexaenoic acid) is important for normal brain and vision development. The increased intelligence and academic performance of breastfed compared with formula-fed infants has been attributed in part to the increased DHA content of human milk.

Cultures whose diet is high in DHA have a lower incidence of degenerative diseases of the central nervous system, such as multiple sclerosis. Some children with ADHD and poor school performance have been shown to have insufficient DHA in their diet.

EPA (eicosapentaenoic acid) is also important in brain and eye development and function. EPA has been used to treat depression, bipolar disorder, Huntington's chorea, chronic fatigue syndrome (myalgic encephalomyelitis), obsessive compulsive disorder, and schizophrenia.

According to Dr Shawn Somerset of the School of Public Health at Griffith University in Australia: "No study has proved that eating more fish will make you smarter."

So it is not true that the more fish you eat, the smarter you become. If this were so, then Eskimos, who eat perhaps the highest amounts of fish as any people anywhere in the world, would all be geniuses. Yet having survived for so many centuries in such a brutally harsh environment, perhaps they are.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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