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Nutrition, mental health and behaviour

30th January 2006

A healthy diet can do more than lead to a healthy body. Courtney Van De Weyer reports on the latest research linking nutrition to behaviour and mental health.

Recent years have seen the popular media awash with stories of the effect of food on mental health and behaviour. Mostly focusing on essential fatty acids, articles have promised that certain foods (and more often, food supplements) can improve your child's behaviour, lift your depression or halt your cognitive decline.

The reason for these articles has been a growing number of research studies looking at the link between diet and brain. With the growing interest in food and the nation's diet, a press-release detailing the results of a new trial linking food and the brain can now lead to a wave of press attention – and then often a run on the fish counter or the supplement shelves.

Image of woman curled up on bedStudies have found significant correlations between what a population eats and the level of depression it suffers. However, despite reports in the popular press, there is no clinical evidence that popping fish oils or multivitamin pills will cure depression.

The controlled trials so far have mostly tested nutrients as add-on treatments to traditional antidepressant drugs. Here the evidence is firmer – improved levels of nutrients may help the antidepressants work better. Further research into why this is so is necessary.

Image by TS Whalen

There have always been anecdotes about how particular foods affect the brain. Whether it is grandmotherly advice about fish being 'brain food' or parents swearing that their child's tantrums only appear after they eat a tube of Smarties, there is a general level of intuitive acceptance that what we eat affects how we feel.

As can be seen by the media reports, however, these anecdotes are increasingly being backed up by more scientific evidence. This is not a particularly new area; many research scientists have been working over many years exploring how certain nutrients affect the brain. Indeed, some of the first were the very scientists involved in discovering and defining vitamins – often, the very first symptom of a vitamin deficiency is a psychological one.

Hundreds of studies linking diet to mental health and behaviour have been published in peer-reviewed medical journals. The studies have ranged widely in subject matter and method – from comparing the intake of a certain food in a country with the prevalence of a mental illness, to measuring the level of certain nutrients in the bodies of patients.

Many of the studies have tested patients’ responses to dietary changes in randomised controlled trials, considered to be the 'gold standard' for authoritative clinical evidence.
For the past eighteen months, Sustain – in partnership with the Mental Health Foundation – has been collating this published evidence that shows how what we eat affects how we feel and behave.

The outcome of this work has been two reports – one produced by Sustain for the food and farming policy sector and one produced by the Mental Health Foundation for the mental health sector.

The reports detail how food appears to affect the brain throughout the lifecycle, beginning with pre-conception, continuing through foetal development, childhood and adolescence, adulthood and into old age. They also explore the evidence linking diet to four specific mental illnesses – attention deficit hyperactivity disorder, depression, schizophrenia and Alzheimer's disease.

Ingredients list from food packetHumans are now eating a diet which would be unrecognisable to our prehistoric ancestors, even though our nutritional requirements are much the same.

We have moved progressively away from healthy whole foods such as leafy vegetables, wholegrains, fruit and lean meat, towards a diet rich in fats, salt and sugar and low in essential micronutrients.

Epidemiologists have clearly linked this change of diet with rising rates of coronary heart disease, some cancers, and a wide range of conditions linked to obesity, such as diabetes.

However, much less research, so far, has examined what this same diet might be doing to our minds, as well as our bodies.

Image by TS Whalen

The research is then considered in the context of a rapidly changing (in terms of human evolution) food system, highlighting such issues as the nutritional quality of processed food, the change in animal fat composition and the decline in fruit and vegetable consumption. The reports ask the obvious question – if there is a link between diet and mental health and the recent and continuing rise in

It is vital to emphasise that the reports do not seek to suggest that poor diets are a causal factor in all mental health problems, behavioural disorders or mood fluctuations. However, our review of the evidence does suggest that nutrition is a highly plausible and important contributory factor in both the cause and treatment of such conditions. And, although it would be a mistake to overplay the role of food, it would clearly be a mistake to dismiss its contribution.

Unfortunately, it is often dismissed. Any instinct that food might play a role in mental wellbeing does not normally translate into any acknowledgement of the role of diet in mental health or behaviour by ‘official’ sources – be that government departments or most heath professionals.

For mental health patients, diet is rarely, if ever, an issue in their treatment – whether that is a depressed individual seeking initial help from their GP or a hospital inpatient receiving treatment for schizophrenia. Parents of children with behavioural problems experience this most acutely – any suggestion by them that diet may be one culprit in their child's poor behaviour is more often than not dismissed out of hand.

What has been perhaps the most interesting, but hardly the most surprising, outcome of this work has been the realisation that the varieties of nutrients that appear to have a positive effect on brain health are the same nutrients that are known to have benefits for physical health.

These include: minerals such as zinc, magnesium and iron; vitamins such as folate, a range of B-vitamins, and anti-oxidant vitamins such as C and E; and the polyunsaturated acids, particularly a good balance of the essential fatty acids.

At the same time, the nutrients or foods that are seemingly implicated as having a negative effect on brain, and thus mental, health are also the same as those known to be poor for physical health – e.g., too much saturated fat and sugar.

The obvious conclusion is that a generally healthy diet, the same diet necessary for a healthy body – one high in fruits and vegetables, with a wide variety of whole grains, nuts, seeds and legumes and occasional oily fish, lean meat and dairy products – is the same diet necessary for a healthy mind.

Unfortunately, this is not the message that tends to come out of the press reports of new studies or trials. Some of the more promising studies have been touted in the national media as 'proving' that, for example, fish oils (which contain the omega-3 fatty acid) will improve a child's reading ability or will alleviate an individual's depression.

Of course, no one study proves anything. Also, because trials must be controlled for a single, or a group, of particular nutrients, they are often tested in isolation. But, of course, no one eats nutrients in isolation – they eat food.

Moreover, because it is difficult and sometimes impossible to use food in trials (due to the requirement that the person being studied, and sometimes even the person doing the study, must not know what is being tested), it is often necessary to rely on food supplements.

This can give the misleading impression that simply eating food isn't sufficient; in order to receive the benefit detailed in the trial one must purchase and consume (usually expensive) food supplements – an impression all too happily exploited by the supplement companies. (One argument put forward is that the amount of nutrients required can not be reasonably met by food consumption, thus requiring the nutrient in pill or capsule form.)

Of course, there is still a great deal of research that needs to be done. Many issues need investigation, including:

The specific nutrients necessary for good foetal brain growth. Apart from prescribing a generally healthy diet, there is no real research into the nutrients needed during a woman's pregnancy to ensure proper brain development.

The relationship between children's diets and academic attainment and behaviour in the classroom. Although there is a great deal of anecdotal information, there are still large gaps in the research.

The role of sugar in Attention Deficit Hyperactivity Disorder (ADHD). Studies have been completed which appear to exonerate sugar, but these have often been criticised for design flaws. For example, some trials only lasted one to two days and included very small numbers of children. Larger and longer trials are needed.

The impact of a better diet – as opposed to increased supplementation – on anti-social behaviour.

Why, if long-chain omega-3 fatty acids (which can only be ingested by eating animals) appear so important for brain and other physical health, vegetarians don't appear to suffer higher rates of mental illness and are generally considered healthier than meat eaters.

Whether a person experiencing dementia or Alzheimer's disease could slow or halt the decline through better diet – again, there is anecdotal evidence of this, but it hasn't been backed up by any formal research.

These issues represent just a selection of a long list of unanswered questions about the role of diet in mental health. It is clear that a great deal more research must be done. However, it would a mistake to discount the evidence that already exists – after all, acceptance of causal factors in diet-related health is a gradual process. It is only surprisingly recently that diet was recognised as a factor in coronary heart disease, and only then after many years of research and campaigning.

Courtney Van De Weyer is the Food and Mental Health Project Officer at Sustain. She is the author of Changing Diets, Changing Minds: How food affects mental well being and behaviour. Copies are available from Sustain for £10.00 (Sustain, 94 White Lion Street, London N1 9PF. Tel: 020 7837 2250) or can be downloaded free of charge from www.sustainweb.org/pub_down.asp