A new study led by researchers in the UK found that an overall healthy "whole food" diet comprising a high proportion of fruits, vegetables and
fish, protected middle aged people against depression compared to a processed food diet containing a high proportion of high fat dairy food, processed
meat, fried food, refined grains and sugar-laden desserts.
The study was the work of researchers based at the Department of Epidemiology and Public Health, University College London (UCL), UK and the Institut National de la Santé et de la Recherche Médicale (INSERM), University of Montpellier, France, and is published in the November issue of the The British Journal of Psychiatry which is available online.
In their background information the authors explained that much research on diet and depression tends to focus on individual nutrients so they thought they would look at links between overall dietary patterns and depression.
For the study they looked at data covering 3,486 participants of average age 57 years (nearly three quarters were men) who were part of the Whitehall II study.
The Whitehall II study was set up by co-author and UCL Professor Sir Michael Marmot to investigate links between disease and social class, psychosocial factors and life style. It began by looking at the health of working people, and is now also looking to answer questions about how previous and current circumstances affect health and quality of life in an ageing group of participants.
The data allowed the researchers to identify two dietary patters: a whole food diet and a processed food diet. The whole food diet comprised mainly fresh fruits and vegetables and fish, while the processed diet comprised mainly sweetened desserts, fried foods, high fat dairy foods, processed meat and refined grains.
To assess depression, the researchers used self-reported data that had been gathered five years after the dietary data using the CES-D scale.
CES-D, short for Center for Epidemiologic Studies - Depression scale, is a commonly used self-report questionnaire for assessing depression. It asks a series of multiple choice questions about how the participant has been feeling over the past week, covering topics such as concentration, loss of appetite, worry, how well they have been able to shake off depressive moods, quality of sleep, feelings of loneliness, self-worth, energy levels, and so on.
When they analysed the results and ruled out potential confounders such as age, gender, education, smoking, exercise, and chronic diseases, the researchers found that:
- Participants in the top 33 per cent (top tertile) of the whole food diet pattern, ie whose diet most closely matched the whole food diet, had a 26 per cent lower risk of receiving a CES-D depression assessment five years later (odds ratio 0.74, with 95 per cent probability of this being in the range 0.56 to 0.99) compared to the bottom 33 per cent (bottom tertile), ie whose diet least closely matched the whole food diet.
- In contrast, participants whose diet was high in processed foods had a 58 per cent higher risk of receiving a CES-D depression rating five years later.
"In middle-aged participants, a processed food dietary pattern is a risk factor for CES-D depression 5 years later, whereas a whole food pattern is protective."
According to BBC News, co-author Dr Archana Singh-Manoux, who works at UCL and INSERM, suggested there was a possibility that the finding could be explained by a lifestyle factor they had not accounted for.
In other words the study does not prove that a processed food diet causes depression: it could be that people destined to become depressed become inclined to eat more processed foods, that there is a yet undiscovered factor behind both.
However, when results as strong as these emerge, and a consistent pattern linking diet and depression is found by several studies, it would tend to suggest that a healthy diet does protect against mental ill health.
The Chief Executive of the UK-based Mental Health Foundation, Dr Andrew McCulloch told the BBC that:
"This study adds to an existing body of solid research that shows the strong links between what we eat and our mental health."
He said major studies like this were crucial in helping us understand more about how diet contributes to mental illness. He said people in the UK were increasingly adopting unhealthy diets, and eating less nutritious and fresh food and more saturated fats and sugars.
"Dietary pattern and depressive symptoms in middle age."
Tasnime N. Akbaraly, Eric J. Brunner, Jane E. Ferrie, Michael G. Marmot, Mika Kivimaki, and Archana Singh-Manoux.
The British Journal of Psychiatry, Nov 2009; 195: 408 - 413.
Additional sources: UCL, BBC News.
Written by: Catharine Paddock, PhD