Feature: Mood food
6 February 2007. By Lisa Melton
In the last 200 years, the human diet has changed dramatically: fish oils, fruit and vegetables have taken a back seat to sugar, saturated fats and salt. Amid worries that such changes are affecting our health, nutritional science has become a major area of research. But are dietary changes also affecting our behaviour?
Fact and fiction are proving hard to disentangle: systematic studies of the impact of modern diets on behaviour are rare. There are hints that some foods can affect mood, but these are often based on small effects in trials on small numbers of people, and the results have often been overinterpreted and extrapolated too far, by the press in particular.
"People pick up the idea that a magical food is going to transform their child's social problems and stop rioting in the streets. That's nonsense. We need a calm, sober evaluation of the data," says David Benton at Swansea University. "Changing nutrition at the most will change biologically determined potential. Whether that potential is realised will depend on an appropriate psychological and social setting."
Cheery chocolate
'Chocoholics' swear by the uplifting properties of a quick 'fix'. Indeed, researchers have found that cocoa contains pleasure-enhancing ingredients: methylxanthines, caffeine, theobromine and the 'bliss molecule' anandamide. This euphoria-inducing cannabinoid is in dark chocolate and cocoa powder, but not in white chocolate, which seems to lend weight to claims of its psychoactive prowess.
Not so, according to Professor Benton: "Calculate how much you'd have to eat to improve your mood." A 70 kg person would have to eat 100 bars of chocolate at one time to achieve a marijuana-like high. So, more than likely, another mechanism is at work. "We are programmed by evolution to like things that are sweet and fatty, to avoid starvation. Sweet and fatty foods hit the reward mechanism in the brain and they release endorphins," he says.
In the last 200 years, the average UK person's annual sugar consumption has risen from an estimated 10 kg to 70 kg. So might high intakes of sugar be involved in behaviour changes? Such links were largely dismissed in the mid-1980s, based on small studies, but there is growing evidence that they need to be revisited. For example, a study in 2002 fed rats on excessive amounts of sugar; when the rats did not get sugar, they had withdrawal symptoms similar to those of morphine. And a 2006 study of Norwegian students found that high levels of consumption of sugary soft drinks were associated with mental illness and conduct problems.
Additive alert
Artificial additives have a reputation for adverse effects on behaviour, particularly in children. The food industry insists that such additives have been tested and shown to be safe - indeed, E numbers mean that the compounds are approved for use in the EU. However, behaviour change is not something that toxicologists normally test, points out Alexandra Richardson, a physiologist at the University of Oxford and Co-director of the charity Food and Behaviour Research.
In 2004, a study that pulled together data from 15 trials on the behavioural effects of artificial food colourings concluded that such chemicals did contribute to hyperactivity in children with attention deficit hyperactivity disorder (ADHD). "Anyone who is worried about their children's behaviour would do well to avoid tartrazine [E102] and coloured dyes," argues Dr Richardson. "Why are these things in children's food in the first place? They have no nutritional value, only cosmetic." The Food Standards Agency recognises that "this remains an area of scientific uncertainty," and has embarked on a project to address this issue. Results are expected this year.
Fish and fat
Brains are roughly 60 per cent fats, so the fats we eat - or fail to eat - could be changing the architecture of the brain. Docosahexanoic acid (DHA) and eicosapentaenoic acid (EPA), long-chain omega-3 fatty acids found in oily fish, are receiving a lot of attention as they are essential for normal brain development and function. "There's work showing that omega-3s are depleted in depressed patients and some evidence that children with disorders like ADHD and autism are deficient in these essential fatty acids," says Dr Richardson.
Fish oil contains abundant DHA and EPA, but green vegetables, seeds and vegetable oils contain only shorter omega-3 fatty acids, and modern food processing strips many of these out. Return EPA and DHA to the diet, and children's behaviour improves, according to Dr Richardson. She studied 100 children of normal ability with coordination problems or dyspraxia, who were underachieving and unruly at school. In a trial, half the children received fish oils for three months while the rest took an olive oil placebo. Some 40 per cent of the children given supplements made dramatic improvements in reading and spelling, while the control group progressed only at the expected pace.
It was an exciting finding that sparked a media furore. Sales of fish oil supplements rocketed. But the picture remains confusing. "There isn't enough evidence to recommend these supplements to the general population," argues Claire Williamson from the British Nutrition Foundation. She points out that out of six trials in children with ADHD or related problems, three found no effect with essential fatty acids. And there are almost no studies suggesting that omega-3 supplements will make normal children healthier or brainier. Researchers argue that properly designed, large studies need to be carried out.
Even so, convinced that boosting fish oils can improve concentration and learning, the Durham Local Education Authority proposed that children in year 11 should be given omega-3 supplements for three months and their progress followed for nine months. In September 2006, they began the controversial programme in 36 schools. The initiative was widely reported in the media and branded a 'clinical trial'. But Oxford scientists are scathing. "It borrowed the reputation of the only proper study," says Dr Richardson. "It is masquerading as a trial, dishing out fish oils to a whole group of children, from which you'd expect to learn absolutely nothing."
"My criticism of the Durham exercise is that it is not properly monitored or controlled so we won't know what would have happened to the children anyway," says Professor John Stein at the University of Oxford, where much of the UK research on omega-3 fatty acids has been done.
He is impressed, however, by the improvements he has seen in children with dyslexia, dyspraxia and ADHD taking fish oils. He believes that the high-speed magnocellular pathway in the brain, which helps to perceive movement and locate objects in space, is particularly vulnerable to fatty acid deficiencies. Omega-3 fatty acids may help to smooth out the problems.
Balancing act
In 2002, Bernard Gesch and colleagues at the University of Oxford conducted a pilot study in a prison. "Many prisoners make poor food choices, eating diets lacking in vitamins, mineral and essential fatty acids," he says. "The health implications of poor diets are well understood, but we wanted to assess the implications for behaviour of improved diets."
In the study, young offenders at Aylesbury high security prison volunteered to take essential fatty acids and key vitamin and mineral supplements for nine months. More serious offences, including violence, dropped by 37 per cent in the prisoners who supplemented their diet, while the control group remained unchanged. "These findings raise the question of what might have happened to these young men if they had been better nourished in the first place," notes Mr Gesch. The Wellcome Trust has recently funded a follow-up trial to verify these early results.
The World Health Organization has also recognised the broader implications of the evidence, commenting in 2006: "Certain dietary choices, including fish consumption, balanced intake of micronutrients, and a good nutritional status overall also have been associated with reduced rates of violent behaviour." So avoid that industrial food, aim for a balanced diet, and bon appétit.
Image credit: Libby Welch
Lisa Melton is a science writer based in London
References
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- Richardson AJ, Montgomery P. The Oxford-Durham study: a randomized, controlled trial of dietary supplementation with fatty acids in children with developmental coordination disorder. Pediatrics 2005;115(5):1360-6.
- Eves A, Gesch B. Food provision and the nutritional implications of food choices made by young adult males, in a young offenders' institution. J Hum Nutr Diet 2003;16(3):167-79.
- Schab DW, Trinh NH. Do artificial food colors promote hyperactivity in children with hyperactive syndromes? A meta-analysis of double-blind placebo-controlled trials. J Dev Behav Pediatr 2004;25(6):423-34.
- di Tomaso E et al. Brain cannabinoids in chocolate. Nature 1996;382(6593):677-8.
- Prüss-Üsten A, Corvalán C. Preventing disease through healthy environments: towards an estimate of the environmental burden of disease. Geneva: World Health Organization; 2006.