Professor Malcolm Peet has already carried out pioneering controlled trials of treatment with omega-3 fatty acids in both schizophrenia and depression. His latest study in the British Journal of Psychiatry (see Peet 2004) focuses on cross-national data, and shows that schizophrenia is more severe in countries where the national diet is higher in sugar and saturated fats, while depression is more common in countries with a lower consumption of omega-3 fatty acids from fish and seafood.
This kind of study obviously cannot address cause and effect. But randomised controlled trials (RCT) can - and many such trials showing clear effects of diet on behaviour, learning and mood (including Professor Peet's previous work) can already be found on our website (search on 'RCT' for a list of these). In other recent papers, Professor Peet has also offered some plausible mechanisms for the links he has found between diet and mental health. See in particular
Peet 2004, Diet, diabetes and schizophrenia: review and hypothesis.
Peet 2004, Nutrition and schizophrenia: beyond omega-3 fatty acids.
The day Pat Webster read that schizophrenia often occurs in families with a high incidence of heart disease, it was like switching on a light.
Of course. Schizophrenia had affected three generations of her own family, including her son, while both of her parents died of heart attacks at the age of 60. The suggestion that high-fat diets might be a causal factor in schizophrenia as well as heart disease, seemed entirely possible to her.
"This is the way I see it," says Pat, who is the co-ordinator and founder of the Hearing Voices Network in Dundee, a support and information network for schizophrenia sufferers. "In our family, we're prone to either heart attacks or schizophrenia, so it could be there's a quirk in our nutrition. It could be to do with fatty acids."
Pat read about the possible link between diet and mental illness in an article by the late Dr David Horrobin, a neuroscientist who lived in Scotland until his death in April last year. He was not the first to make the association and will certainly not be the last. In fact, there is a growing body of evidence to back up the theory, particularly on the importance of fatty acids found in fish oils.
The latest piece of research is by Professor Malcolm Peet, a consultant psychiatrist for the NHS, previously attached to the University of Sheffield, and associated with Food and Behaviour Research, a charitable organisation dedicated to researching the links between nutrition and human behaviour. His study looks at whether dietary differences could explain why depression is more common and schizophrenia more severe in developed western countries than in poor developing countries.
Writing in the British Journal of Psychiatry, published by the Royal College of Psychiatry, Professor Peet has shown that in countries with high rates of depression, the national diet is typically low in fish and seafood. Where diets are high in refined carbohydrates and saturated fat, schizophrenia sufferers fare worse.
Those who believe diet is a causal factor in mental illness are excited about such research. They believe it could have implications for the treatment, not to mention the prevention, of mental ill health, and might also release patients from their over-reliance on drugs.
Yet some remain unconvinced. Dr Stephen Lawrie, a consultant psychiatrist at the Royal Edinburgh Hospital, says that, while it's almost certainly a good thing for a patient's general health to eat more fish and seafood, the research is still not conclusive on the link to mental health. "There's no specific evidence that having a good diet affects mental health," he says.
One shortcoming of Prof Peet's research, he says, is that it focuses on national diets and national patterns of mental illness rather than those of specific individuals. What's more, while schizophrenia sufferers have worse diets than the general population, as proven in a study by Professor Robin MacReadie of Crichton Hospital, Dumfries, last year, that might be a result of their illness rather than a cause of it.
Prof Peet's research, however, is only one part of a small avalanche of studies which have looked at the effects of diet on individual patients. "To deny any link between diet and mental health seems untenable in the face of the evidence," says Dr Alex Richardson, a senior research fellow at Mansfield College, Oxford University, who is also attached to FAB Research.
There is clearly a need to follow Prof Peet's study with trials at individual level, she says. However, she stresses that a lot of research has already been done.
Much of this has focused on certain fatty acids, called Omega 3s, which are essential for proper chemical function in the brain, regulating hormones and the immune system. Fish oils are rich in Omega 3 fatty acids called EPA and DHA. With regard to depression, several published trials have shown that omega-3 (particularly EPA) can reduce symptoms when used in addition to medication. With schizophrenia, four out of five published studies have shown benefits from EPA. However, in the West, we now eat far less Omega 3 than we did and far more of other fatty acids, called Omega 6.
"In hunter-gatherer diets, the ratio of total Omega 3 to Omega 6 was less than 5:1; now it's often as high as 20:1 in favour of Omega 6," says Dr Richardson. So, could bingeing on fry-ups for a month affect mood? Yes, says Dr Richardson: the combination of toxic fats and excessive sugar and fat "wouldn't do any good at all" for your mental health.
Vegetarians also need to take care. They should take flaxseed oil which contains a type of Omega 3, if not the kind preferred by the body. Eating for good mental health, says Dr Richardson, should involve cutting refined carbohydrates such as sugar and white flour (if unused, the body converts it to fat); avoiding processed foods containing hydrogenated fats (switch to rapeseed oil for cooking, not sunflower or safflower); and above all, including Omega 3 fatty acids. The best sort can be obtained from oily fish or a high-quality supplement.
However, diet is no panacea for depression or schizophrenia. Firstly, says Dr Richardson, poor diet is only one of many factors that can contribute to mental illness and secondly, the constitution of one person is different from the next, so changes in diet will affect them differently.
More research is needed to discover just how important diet is in comparison to other factors. Yet it could be a step towards reduced reliance on pharmaceutical solutions.
"My view is that you have to listen to your body," says Pat. "Nutrition is one of the things we should be looking at."
For more information on fish oil and mental health, visit