In a new review study, researchers found evidence that the right diet can prevent or alleviate depression is weak.
The research was conducted by a team at Leiden University.
The link between diet and depression has become a popular news story in recent years.
But the field is still young, and many of the academic articles that conclude there is a link between diet and depression are reviewed: papers in which the author provides an overview of the current knowledge.
In the study, the team analyzed these reviews and that the authors often draw much stronger conclusions than the underlying studies would justify.
The researchers studied 50 review articles, distinguishing between narrative reviews (also known as literature reviews), systematic reviews, and meta-analyses.
They discovered that a third of the literature reviews reached a strong conclusion about the link between diet and depression, whereas none of the meta-analyzes found such a strong link.
They also did their own meta-analysis: if you take all the experimental evidence together, no strong link can be found between your diet and preventing depression, or for diet being able to help treat it.
The literature reviews are often too emphatic in their findings, therefore. And those conclusions find their way to the public and practitioners.
In addition, an author can unintentionally give too much weight to his own research or research that supports his hypothesis.
This is called confirmation bias and is probably an important reason why the conclusions in literature reviews are too strong.
There is much less chance of this bias in systematic reviews and meta-analyzes—and therefore less chance of the conclusions being too strong.
One author of the study is Florian Thomas-Odenthal.
The study is published in PLOS ONE.
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