September 26, 2018

expert reaction to observational studies on diet and depression

Research, published in Molecular Psychiatry, shows that adhering to a healthy diet appears to confer some protection against depression.

Dr Brendon Stubbs, NIHR Clinical Lecturer, Institute of Psychiatry, Psychology and Neuroscience, King’s College London and Head of Physiotherapy, South London and Maudsley NHS Foundation trust, said:

“This is an important, novel and well conducted study which adds further impetus to encourage us all to participate in healthy lifestyle to reduce our risk of developing depression in the future.  We have known for some time that what we eat can influence our physical health, but the impact on mental health and specifically depression had not previously been comprehensively evaluated.  This robust meta-analysis provides interesting evidence to suggest that adhering to a Mediterranean or anti-inflammatory diet (e.g. a diet high in fish, pulses, rice, fruit, vegetables) may protect against the emergence of depressive symptoms in the future.  The potential public health implications are considerable when one considers the extensive literature about eating a Mediterranean and avoiding pro-inflammatory diets (e.g. saturated fats, refined carbohydrates, and red meat) for positive physical health outcomes.

“Whilst the results are novel, some limitations should be noted.  First, people struggle to accurately recall exactly what they have eaten in the past and this research relies heavily on people’s ability to accurately recall their dietary intake in the past.  Second, people who tend to eat a Mediterranean diet or lower pro-inflammatory diet often engage in other positive lifestyle factors (e.g. exercise more, less likely to smoke, have better sleep) or have less physical health issues or obesity which are also known to influence depression risk.  While the authors did adjust for some of these, it is difficult to truly account for all of these effects and other factors could have contributed to the observed relationship between diet and depression.  Third, most of the studies included are cross sectional and whilst the authors conduct a subgroup analysis to look only at longitudinal research, clearly we cannot say that our diet causally contributes to the onset of depression from this research.  Finally, the methods of collecting dietary information and the measures of “depression” are highly variable across all of the studies which adds further uncertainty of the overall accuracy of the effects noted, but the signal seems consistent that the Mediterranean and anti-inflammatory dietary patterns are positively associated with a reduced odds of depression.”

Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“Whilst better diets may well help prevent depression, the current evidence is not sufficient to prove plant-rich diets can prevent depression as most of the evidence so far simply shows that those with poorer mental health eat worse, so it may be that those more prone to depression also choose less healthy (so less plant based food) diets rather the poorer diets causing poor mental health.

“This systematic review and meta-analysis only looks at observational studies and so a heavy dose of caution is needed. The only way to prove whether the links are genuine is to conduct large randomised trials in people at risk of depression – such trials would take considerable effort but seem worthwhile to conduct – so far only small trials have been conducted. We really need large, well powered, intervention trials to test this to give this idea any credibility.

“Also the link to inflammation as a plausible mechanism to explain a link between diet and mind health is highly tenuous.

“Thus, whilst easting healthier is good for many reasons, we need more evidence before we can say plant rich diets can improve mental health.”

All our previous output on this subject can be seen here: http://www.sciencemediacentre.org/tag/depression/

Declared interests

Prof Naveed Sattar:  No conflicts of interest

None others received.