posted 5th June 2022
Depression and low mood are not separate from the rest of your bodily health: the right diet can help reduce your risk. A lovely cup of tea. Anyone who grew up watching British television in the 1980s and '90s, as I did, will be well versed in the near-miraculous soothing properties of a lovely cup of tea. Had a bad dream?
Have a cup of tea. Pub firebombed by East End gangsters? Have a cup of tea. And the calming powers of a cuppa might be more than simply a soap writer's trope, since there is some evidence that tea and tea extracts can lower cortisol expression and biomarkers of inflammation, both features of the stress response.
But, wherever you are in the world, food is used to influence affective states - whether it's a soothing bowl of congee or chicken soup when you are unwell, or a piece of chocolate when you are feeling miserable. The question is, how deep is food's potential to affect how people feel? Can food improve your mood in a significant or lasting way - and, if so, how? Might we eventually be able to prescribe nutritional interventions to help people feel better?
These are not inconsequential questions. Depression affects approximately 280 million people worldwide, and antidepressant medications - though they have offered relief for many - are not as effective as we need them to be. Furthermore, psychotherapy - an effective treatment for depression and other mood disorders - is simply not accessible enough for many people. One assessment found that the median time that a young person waited to access therapy in the UK was 60 days. Many people wait even longer. In a survey of therapists across the US, conducted by The New York Times at the end of 2021, a third said that it would take at least three months for an appointment to open up. It is a similar story in Australia. Also of concern is the number of patients - as many as 30 per cent, by one UK estimate - whose illness does not meaningfully improve with treatment, what is termed 'treatment-resistant depression'.
The insufficiency and inaccessibility of our frontline depression treatments has led to a reassessment of our understanding of the mechanisms underlying depression. It has encouraged a move away from the 'serotonin hypothesis' (that reduced activity of serotonin in the brain is the cause of depression) and toward a focus on the interaction between the immune system, the brain and mental states. This field of research, called psychoneuroimmunology, is driving a revolution in the conceptualisation of depressive illness and, consequently, its treatments.
The shift in focus also opens up potential new avenues for individual management of depressive symptoms; we might have more power than we thought to support our own brain health and recovery. Though there is no magic bullet, emerging and accumulating evidence indicates that modifiable features of our lifestyles that influence our immune systems - including nutrition - are important factors in our vulnerability to, severity of and recovery from depression. Knowing a little more about the relationship between nutrition, immunity and mood could enable people to stack the odds more in their favour.
inflammation and other factors link food with mood
Inflammation is essential for health: when the body recognises a pathogen, the immune system mounts an inflammatory response, with immune activation returning to baseline once the threat has been eliminated. However, long-term infection and aspects of lifestyle such as poor diet and stress can lead to chronic inflammation - a key feature of many diseases. Reviews have shown that people with depression have higher levels of inflammatory markers than non-depressed people. And participants in 'immune challenge' trials, in which they are exposed to compounds that trigger an immune response, develop depressive symptoms.
Fascinatingly, the severity of depressed mood elicited in these studies is associated with the concentration of cytokines (inflammatory signalling molecules) measured in the blood. Cytokines have demonstrable effects on a range of depression-related features. For instance, they can cause the tight junctions of the blood-brain barrier to loosen, allowing immune cells and other molecules to cross into the brain, triggering an inflammatory response. They also increase the reuptake of dopamine in the synaptic cleft, leaving less of this neurotransmitter (important for motivation and goal-directed behaviour) available in the brain.
Immune dysregulation is a plausible and unifying biological mechanism for many of the risk factors in the development of depression - which range from genetics to comorbid diseases to psychosocial problems such as unemployment. And interventions that target inflammation hold promise as effective treatments for depression, including the scourge of treatment-resistant depression. Here's where food comes in.
The epidemiological evidence is consistent across time and across cultures: the closer a person adheres to their nation's guidelines for a healthy diet, whether in the UK or France, Spain or Australia, the lower their risk of later development of depression. What's interesting about this research is that it is not advocating for any individual 'superfoods' - wherever you are in the world, the message seems to be that a whole-food, plant-heavy, fibre-rich diet that is low in added sugar, trans fats and processed meat products is associated with protection from depression.
While the specific mechanisms involved are largely still to be defined, there is plenty of data to sink our teeth into. A tool called the Dietary Inflammatory Index (DII), which assesses the potential of an individual's diet to promote inflammation, has been used in numerous clinical trials. The emerging consensus is that the higher the inflammatory potential of a person's diet, the worse their brain function will tend to be. A large prospective study that followed thousands of people for an average of five years found that those with a more pro-inflammatory diet had a greater risk of developing depression.
According to the DII, the foods and nutrients with the most anti-inflammatory potential include fibre, beta carotene (found in brightly coloured vegetables), garlic, ginger, turmeric, vitamins A, C, D and E (fruit, vegetables, oily fish, nuts), green and black tea, flavones and flavonoids (berries), and Omega-3 fats (oily fish and seafood). (We'll discuss how to incorporate more of these into your diet below.) There are a number of other pathways through which food could affect mood. The gut is colonised by trillions of microbes, collectively known as the gut microbiome. In return for being supplied with the right substrate, these microbes help to maintain the integrity of the gut lining and produce a range of byproducts that can be beneficial for mood regulation. And food might play an even simpler role in mood regulation through the resolution of nutritional deficiencies. For example, Vitamin B6 is essential for the synthesis of serotonin, dopamine, GABA and noradrenaline, meaning that deficiency in this nutrient leads to the downregulation of these mood-regulatory neurotransmitters.
perspectives on mental health are expanding to include food
Nutritional psychiatry, the discipline that looks at the role of food and nutrients in mental health, is relatively young, but the idea that these things are connected is not new. More than 100 years ago, John George Porter Phillips authored a study in which treatment with soured (fermented) milk was reported to improve depressive symptoms. And recent intervention studies, such as the SMILES trial (Supporting the Modification of lifestyle in Lowered Emotional States), indicate that there is promise in the use of food and nutrition to improve outcomes for both patients and the general public.
Of course, nutritional changes do not in themselves mean an end to depression. And food choices are not made in a vacuum: factors such as income, geographic location, education, free time and food advertising will affect food choices, meaning that local authorities and central governments have an important role to play in making nutritious food accessible. But the complementary fields of psychoneuroimmunology and nutritional psychiatry signify a fundamental shift in our approach to mental illness. Rather than treating the mind as separate from the body, we can begin to understand the influence of the immune system and metabolism on mental states.
The complex and essential contribution of nutrition and other lifestyle factors to mental health is why I practise what I call 'whole body mental health', combining evidence-based modifications in lifestyle with psychological therapy to improve outcomes for my patients. This approach means we are tackling the individual's concerns from two directions - from the brain down, and from the body up. But this information isn't just for people with a diagnosis. I follow the evidence myself, consuming a nutrient-dense diet to help support my own psychological resilience and reduce my risk of developing depression. With the guidance to follow, I will illustrate how you too can pursue a more mood-supportive diet.
