Whether genetic or environmental factors have more bearing on intelligence is a debate that has raged for years. Now a new factor, nutrition, is vying for attention as studies show how the foods we eat may affect brain development and sustenance. And as nutritional neuroscience gains ground in research circles, popular books on "brain foods" are filling more shelf space in our book stores.
So can we add nutrition to the nature- nurture debate? Can we say that certain foods are crucial for the development of the brain? And that by eating more fish, for example, we will have better memories and better concentration, and not suffer from Alzheimer's disease in old age? Or that by eating more oats or turkey we will be less likely to suffer from depression or bad moods?
Dr Jacqueline Stordy, an English nutritionist, has researched the value of omega-3 fatty acids - found in oily fish such as tuna, mackerel, sardines and salmon - for people with learning disorders. She believes her evidence points to fish as an important brain food.
"It is true in terms of intellect, true in terms of mood and depression, true in terms of concentration and attention. And true for a lifetime - from two years before conception to old age." In a forthcoming book, The LCP Solution - The Remarkable Nutritional Treatment for ADHD, Dyslexia & Dyspraxia, Stordy and Malcolm Nicholl set out the evidence for the nutritional importance of omega-3 fats for children and adults with specific learning disorders.
"The brain has a higher percentage of fat than any other organ in the body, and half of this fat is made up of essential fatty acids called long-chain polyunsaturated fatty acids (LCPs). Individuals with dyslexia, dyspraxia, attention deficit disorder (ADD) and attention deficit hyperactivity disorder (ADHD) have deficiencies in these LCPs," says Stordy.
In a study carried out in Northern Ireland, children with ADHD behaved better and had longer attention spans when given an omega-3 supplement derived from fish oil and evening-primrose oil. Stordy believes that omega-3 and omega-6 fats (another LCP) are also very important for women before conception, during pregnancy and lactation and up to six months post-natally, both to ensure adequate fatty acids are laid down for brain development in the foetus and so the mother can redress her own deficits following pregnancy and lactation.
Stordy also notes that people who eat a lot of fish, such as the Japanese, have relatively little dyslexia and less depression.
Helen Roche, a lecturer in molecular nutrition in the department of clinical medicine at Trinity College, Dublin, is wary about making radical claims about the importance of omega-3 polyunsaturated fats. Roche has compared the levels of DHA, the most important omega-3 polyunsaturated fatty acid in the brain, in the blood of those with and without Alzheimer's disease. "We found lower levels of DHA in Alzheimer's patients, but that doesn't mean the lack of DHA is causing memory loss or the disease. It could only be a marker for another, as yet unknown process," says Roche.
Meanwhile, books such as Brain Food: The Essential Guide To Boosting Brain Power, by another English nutritionist, Lorraine Perretta, and Your Miracle Brain, by Jean Carper, an American writer, are suggesting foods that contain complex carbohydrates - fruit, vegetables, seeds, nuts and whole grains in the form of wholemeal pasta, brown rice and quinoa - are the key to academic excellence.
Complex carbohydrates are believed to be the best foods for supplying brain fuel because of the way they slowly release energy - the brain needs a constant supply as, unlike other organs, it does not store any itself.
The refined carbohydrates found in sweets, biscuits, soft drinks and chocolate are not as good, because they contain easily digestible sugars that break down into glucose fairly quickly, flooding the blood.
"These surges are often followed by dramatic drops in glucose delivery, resulting in decreased energy, shorter attention span and an inability to concentrate," writes Perretta.
Protein foods are also vital for transmitting information from the brain to other organs. The brain is like a dispatch centre from which all neurotransmitters leave to carry messages to nerve cells around the body. Neurotransmitters are made from amino acids found in protein foods, such as meat, fish and cheese. The body needs vitamins and minerals to convert the amino acids to neurotransmitters.
Up to this point, nutritionists agree on the value of essential fatty acids, complex carbohydrates and proteins for the brain. But when it comes to choosing brain foods, opinions vary. Some emphasise the importance of certain minerals and vitamins for brain power. Calcium, magnesium and zinc are considered vital for memory and concentration, for example; vitamins A, C and E are deemed particularly important for promoting and preserving memory in old people.
Another area of growing interest is plant nutrients or phytochemicals and, in particular, flavonoids, a group of phytochemicals valued as antioxidants. They help to prevent the degeneration of brain cells by keeping their membranes intact, ensuring the fast transfer of information and so giving us better concentration and memory retrieval.
Anthocyanidin, a flavonoid found in beetroot and dark berries, is believed to protect brain-cell membranes. Also, amino acids such as tyrosine, which is transformed into the brain chemical noradrenaline, and tryptophan, which is converted to serotonin - found in eggs, cottage cheese, oats and turkey - are believed to improve mood and lift depression.
Roche says she would be slow to point to the value of specific foods for their antioxidant properties alone, however. "Any antioxidant will protect brain-cell membranes, because the brain-cell membranes are made up of fats, and increasing the levels of all antioxidants, you prevent oxidative damage of the brain membranes. So when you consume fruit and vegetables, you are getting loads of antioxidants which work synergistically.
"There is huge controversy in the nutrition world about the bioavailability of antioxidants such as the polyphenols in red wine, red fruits and berries. We don't yet know what percentage of these antioxidants are digested and absorbed, so we don't know what proportion of these antioxidants are actually available and active in the body," says Roche.
Stordy concludes that the growing phenomenon of certain foods being deemed excellent sources of particular nutrients is led by consumers. "People drive you to it. They want a more natural approach to health and they ask you what's best. But, really, eating a wide variety of food, and a wide variety of foods within each category of food, is the key."
So while raspberries, tuna, porridge and beetroot may be particularly beneficial, don't leave out the regulars, such as chicken, cabbage, eggs, milk and potatoes.
Jacqueline Stordy's website is at www.drstordy.com
Ten possible brain boosters
Beetroot, Berries, Oats, Oily fish, Turkey, Eggs, Cottage cheese, Tomatoes, Broccoli, Nuts
