Most of us can probably think of a time when food or drink has affected our emotions. Making us feel either good or bad. For me, nothing lifts my spirits more than a nice cup of tea when I’m feeling down. I mean, is there anything a cup of tea can’t fix?

The idea that foods affect our mood isn’t a new one. However, only recently have scientists started to research this concept more thoroughly, in an emerging field called Nutritional Psychiatry.

Nutritional Psychiatry explores the effects and relationships of different foods, nutrients, and dietary patterns on mental health.

So far, several observational studies have shown healthy dietary patterns high in fruits and vegetables and low in processed foods are associated with reduced depression risk. While diets high in processed foods have been linked to increased depression risk.

The diet with the most evidence for reducing depression risk is the Mediterranean Diet (MD). Which is known for being high in vegetables, legumes, whole grains, and olive oil while lower in meat, processed foods, and sugar.

Several mechanisms for how the Mediterranean Diet affects depression have been speculated. These include theories involving fibre and the microbiome, folate, and methylation, omega 3 fatty acids, and inflammation. But the theory which caught my eye was the role of polyphenols.

it’s all about the polyphenols

Polyphenols are colourful compounds found in a wide variety of plant foods. They have antioxidant and anti-inflammatory properties and are classed according to the nature of their carbon skeleton: These include phenolic acids, flavonoids, and the less common stilbenes and lignans.

When considering depression, we know that it is commonly associated with subclinical inflammatory status characterized by an increase in proinflammatory cytokines and neuronal damage – consistent systemic inflammation in the brain and nervous system.

Subclinical means markers may not show on a standard blood test, but rather require further investigation by your integrative doctor or natural health professional

Polyphenols may exert protective effects on mental health via upregulating the body’s natural defense systems, stabilizing free radicals, and reducing oxidative damage to our cells. In addition, neuroprotective properties have been observed, with polyphenols modulating specific cellular signaling pathways involved in cognitive processes.

I wanted to explore this concept further. So I and other researchers at the University of Technology Sydney (UTS) Australian Research Centre in Complementary and Integrative Medicine (ARCCIM) conducted a systematic review of the literature. The aim of this literature review was to assess the effects of polyphenols on the symptoms of depression to help verify polyphenols as a potential mechanism for the efficacy of the Mediterranean diet.

so what’s the research say?

We ended up with 37 papers included in the review. Twenty of the papers were observational which provided a strong foundation for suggesting that polyphenols play a role in depression, but they can only infer correlation in regards to disease risk and prevalence. Seventeen of the included studies were experimental and provide more information about causation in regards to polyphenols exerting a therapeutic benefit for depressive symptoms.

Several different classes of polyphenols were assessed in this review including those from tea, coffee, citrus, nuts, soy, cocoa, legumes, and spices. So all the tastiest foods really!

Summary of current research in this area:
• Twenty-nine of the studies found a statistically significant effect of polyphenols for depression.
• The majority of observational studies looked at polyphenols from tea and coffee consumption and depression risk.
• And the majority of the experimental studies looked at turmeric in randomized control trials for clinical depressive symptoms.
• Several studies showed soy isoflavones being effective at reducing depressive symptoms in menopausal women
• Only a couple of studies tested overall dietary polyphenols intake.
• The polyphenols which currently show the most promise: tea and cocoa flavonoids, curcumin and coffee hydroxycinnamic acid, walnut flavonols, citrus flavanones, and the stilbene resveratrol.

So, am I going to start prescribing chocolate-covered coffee beans and turmeric lattes for all of my depressed patients? Maybe, because those foods are delicious! But, as is often the case, more research is needed. Particularly high-quality randomized control trials in patients with clinical depression for the polyphenols which currently show the most promise.

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