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Overview of the biological mechanisms linking diet and mental and cognitive health

The link between diet and mental health disorders could be explained by the impact of diet on many pathophysiological pathways.
I think the best way to understand the link between diet and mental health disorders is to realise that there’s an overlap between many of the pathophysiological mechanisms in disorders like depression, and for that matter, schizophrenia, bipolar. There’s a lot of overlap there too. And the effects of diet on those pathways. As an example, inflammation. We know that many psychiatric disorders are associated with increased inflammation. And this is now a really well-established biological mechanism implicated in the disorders. Importantly, we know that diet has an important impact on inflammation. We know that a poor quality or Western pattern diet, a diet full of ultra-processed foods high in fat and high in sugar, such a diet is associated with increased levels of inflammation.
There is a measure of inflammation called the dietary inflammatory index, which is a measure whereby we can index how inflammatory a diet can be. The other biological mechanism that’s important is oxidative stress. Again, oxidative stress is present in people with psychiatric disorders. Depression has the best evidence base, but that’s true for schizophrenia, bipolar, and many others. And again, there’s evidence that a poor quality, Western diet increases oxidative stress. And conversely, a higher quality, whole food, Mediterranean traditional pattern from various countries is associated with lower levels of oxidative stress. The other major pathway that’s associated with psychiatric disorders is cell survival and cellular growth.
So we know that levels of apoptosis are increased in people with depression and markers of neurogenesis are decreased. We also know that most antidepressants, for example, work through increasing neurogenesis. And if you block neurogenesis, you block the antidepressant effects of antidepressants. A poor quality diet inhibits neurogenesis and increases apoptosis, and there’s really good evidence from animal studies that a high fat, high sugar diet does this. And conversely, that a healthy diet pattern is favourable in terms of cellular survival markers, such as neurogenesis and apoptosis. Another very important factor which is linked to cellular growth and survival are hormones or circulating factors like BDNF. We know that BDNF levels are decreased in depression.
Also that many effective treatments, from psychotherapy to antidepressants, increase BDNF. And a good quality diet does the same. So a healthy Mediterranean, whole food pattern diet is associated with higher levels of BDNF. Conversely, a Western pattern diet is associated with lower levels of BDNF. So this is another plausible mechanism whereby diet quality might influence the core pathophysiology of depression. So there are several pathways that operate concurrently whereby diet influences the core pathophysiology of the disorder that we are trying to treat.

The link between diet and mental health disorders could be explained by the impact of diet on many pathophysiological pathways.

There are a number of closely linked physiological pathways potentially explaining why and how diet can affect mental and cognitive health.

Although most of the clinical studies that have been done to date on biological dysregulations underpinning mental disorders have focused on depression, other conditions, such as anxiety, bipolar disorder and schizophrenia share these pathophysiologic characteristics and regulatory pathways.

Watch the video in which Professor Michael Berk gives us a broad overview of plausible biological pathways that might be modified by diet.

The following diagram illustrates the role of diet in implicated mechanisms. The green arrows represent how a healthier diet might provide beneficial modifications, whilst the red arrows show the potentially detrimental impact of the Western diet (characterised by a high consumption of ultra-processed foods), impacting both symptomology and metabolic outcomes.

"Depression and other MD - Diagram 2.2"
Overview of the interlinked physiological pathways that impact mental health symptomology and might be modulated via diet. Based on concepts from Marx et al. 2021 (see References).

In the next few steps, we will have a closer look at inflammation, gut microbiota, and neurogenesis as key mechanisms where evidence is available and growing.

Discussion point

Reflecting on the video with Prof Berk and the Role of Diet in Implicated Mechanisms diagram, share your thoughts on how this knowledge might be applicable to your clinical practice.


Marx, W., Lane, M., Hockey, M., Aslam, H., Berk, M., Walder, K., … & Jacka, F. N. (2021). Diet and depression: exploring the biological mechanisms of action. Molecular psychiatry, 26(1), 134-150.

Wollenhaupt-Aguiar, B., Kapczinski, F., & Pfaffenseller, B. (2021). Biological pathways associated with neuroprogression in bipolar disorder. Brain Sciences, 11(2), 228.

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Introduction to Nutritional Psychiatry: Nutri-Psyche

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