Kitchen Still Life with Fish and Vegetables (1850-55) by José María Corchón. Courtesy the Prado Museum, Madrid
Depression and low mood are not separate from the rest of your bodily health: the right diet can help reduce your risk
by Kimberley Wilson + BIO
Kitchen Still Life with Fish and Vegetables (1850-55) by José María Corchón. Courtesy the Prado Museum, Madrid
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.
Approach changes to your eating with openness and patience
There is something that is important to know before attempting to make changes to your eating, and it can be summed up this way: ‘We eat what we like, and we like what we eat.’ We tend to eat habitually, choosing foods and flavour profiles that are familiar. This means that we need a bit of time and a few attempts to warm up to new or unfamiliar foods, flavours and textures.
If you initially don’t like, say, the taste of cauliflower, you’ll want to give yourself a few chances. You might experiment with different cooking methods; most vegetables taste better roasted. It also helps to season well with herbs and spices.
The attitude you take to introducing new foods will make a difference. If you go in with the expectation of not liking something, you probably won’t. Therefore, it’s best to try new foods when you are in a good mood and to approach them with a sense of curiosity.
Your expectations of success will also make a difference to your chances of success. Making lifestyle changes isn’t easy, mostly because your brain likes habit. But you can do hard things – it can be hugely empowering to remind yourself of that. Try it for yourself: list some of the difficult things you have done in the past, including any achievements for which you had to work over a long period of time. How hard is switching the type of bread you eat compared with that? Keep this list somewhere accessible so that you can remind yourself what you are capable of, if and when making changes to your diet begins to feel hard.
Prepare to form some new, manageable habits
The most important factor when it comes to building new eating habits is repetition. It is only by doing or choosing something over and over again that it becomes automatic. To make repetition achievable, your new behaviours should be small enough that they are manageable even when you are at your most tired.
The thing about new habits is… we forget to do them. This is where a habit tracker can be invaluable. This can be a handwritten checklist or an app that you download and use to set reminders for yourself. For example, if you plan to drink more green tea, you can prompt yourself each day with the question: ‘Have you had a cup of green tea this morning?’ Very soon you will begin to anticipate the prompt and will not even need to be reminded.
Another helpful way to make an eating behaviour easily repeatable is to integrate it into something you already do. So, rather than clearing your cupboards entirely of familiar foods, modify the things you regularly eat in a more brain-healthy direction. If you regularly drink black tea (not a bad thing), you could switch out one cup a day for green tea. If you always have a sandwich for lunch, you don’t have to ditch sandwiches for salads; instead, you can swap the white bread for a higher-fibre or wholemeal loaf or add a handful of spinach to your usual sandwich filling. A dramatic overhaul is a recipe for disaster and disappointment. The long game is implementing tiny changes that accumulate over time.
Eat fish for their fatty acids
The long-chain fatty acids EPA and DHA, which are types of Omega-3 fatty acids, play key roles in brain health. Found in marine foods such as oily fish, they contribute to both the architecture of the brain and the modulation of inflammation.
The body cannot synthesise EPA and DHA in amounts that are sufficient for health, so they must be obtained from your diet. In the UK, the NHS recommends that all adults eat two servings of fish per week, of which one should be oily. Clinical studies on supplementation have suggested that 1-2g per day of EPA can be beneficial for mild to moderate depression. And a review of 26 studies, including more than 150,000 individuals, indicated that higher fish consumption is related to lower relative risk of depression. The individual studies varied in how they measured consumption, but two or three portions per week would be significantly higher than the UK average.
Oily fish include anchovies, herring, mackerel, pilchards, salmon, sardines, sprats and trout. A 140g serving of mackerel, for example, supplies all the Omega-3 fatty acids that an adult needs for a week.
What about vegetarians, vegans or those who can’t or won’t eat fish? It is advisable that people who do not eat fish take an algae-based supplement containing at least 250mg of combined DHA and EPA per day. (Please note that omega supplements that supply the fatty acid ALA are unlikely to be sufficient.) Vegetarians and vegans, especially those who are pregnant or breastfeeding, would benefit from supplemental pre-formed DHA and EPA.
Recommendations for increased consumption of oily fish need to be balanced against concerns about contamination and sustainability. Fish can accumulate pollutants from the water they inhabit, posing a potential risk for humans. However, at the moment the scientific consensus is that the benefits of fish consumption outweigh current risks. Girls and pregnant/breastfeeding women are advised to eat no more than two portions of oily fish per week. It is also a good idea to choose smaller, sustainable fish such as mackerel. Consult a sustainability database such as the Marine Conservation Society’s Good Fish Guide.
Focus on fibre, a key food for gut microbes
Supporting a healthy and diverse gut microbiome is likely to be beneficial to mood regulation. The primary food for the population of gut microbes is fibre, acquired by the consumption of a broad range of wholegrains and plant foods – nuts, seeds, herbs, spices, legumes, fruits and vegetables.
If we consume insufficient dietary fibre, the balance of microbes becomes perturbed and the protective mucus lining of the gut is depleted, leaving the gut cells vulnerable. In this condition, the junctions of the gut lining can slacken, permitting the transfer of gut bacteria into the bloodstream. This leads to an inflammatory response that can rumble on for weeks, months, perhaps even years.
Government guidelines in the UK recommend that adults consume 30g of fibre per day; most adults are eating just 18g. Teenagers are also consuming less fibre than their recommended daily intake. A good start is to switch to higher-fibre versions of your staple foods: eg, choose wholemeal rather than white bread; eat brown rice instead of white rice; and eat the skins when consuming potatoes. Wholegrain cereals such as muesli and porridge topped with nuts, seeds and dried fruit get your day started on the right track, and high-fibre snacks like hummus and seed crackers can easily add an extra couple of grams of fibre throughout the day.
Mix a variety of plant foods into your diet
Your gut microbiome benefits from a diverse range of plant foods. While there are 300,000 edible plants on the planet, we eat just a tiny fraction of these, around 200. Recent research suggests it would be a good idea to aim for 30 different plant foods per week. This might sound daunting, but remember that fruits, vegetables, nuts, seeds, beans, wholegrains, herbs and spices all count as plant foods. And yet more than half of our calories come from just three plants: corn, rice and wheat. Clearly there is some work to do. Here are some practical ways to start:
Plus One. Whenever you are eating anything, ask yourself, how could I add another plant food? It might mean slicing a banana into your porridge, adding half a can of beans to your pasta sauce, even sprinkling some chillies on your pizza. This very simple ‘Plus One’ strategy can increase your plant diversity without you having to completely overhaul your diet. Not only will you be supporting gut microbiome diversity but your whole body will benefit from the extra vitamins and minerals from consuming more plants.
Mix it up. I also find choosing premade mixes a very easy win. For example, I make my porridge with a muesli base – a mix of wheat, rye, barley, oat and spelt flakes. So, with no extra effort, I start my day with five plant foods instead of just one. Bags of frozen mixed berries, mixed seeds, and dried and canned mixed beans are all staples in my kitchen.
Veg box. Subscribing to a ‘farm bag’ or ‘veg box’ scheme – which delivers plant diversity straight to your door – is another choice I recommend. Not only do these help you eat more seasonally, they encourage you to try foods that you might not ordinarily pick up at the supermarket.
Eat fermented foods
Increasing the range of plants you eat is important, though a recent comparison study from Stanford University suggests that there is an even faster way to increase the diversity of your gut inhabitants: fermented foods. Fermented products – foods and drinks that have undergone bacterial fermentation – have been a feature of traditional diets around the world for thousands of years. They include kimchi, kombucha, kvass, boza, togwa, kefir, sauerkraut and other naturally fermented pickles, cheese, yogurt and dozens more. Originating as ways to preserve the harvest and supply nourishment through long, cold winters, these foods are now understood to play a beneficial role in gut-microbial diversity and, by extension, our health.
In the Stanford study, 36 people were randomly assigned to either a diet high in fibre or one high in fermented foods for 10 weeks. The fermented food group consumed an average of 0.4 servings per day of fermented food at baseline, increasing to an average of more than six servings. The researchers found that more frequent and larger servings of fermented foods such as kombucha, kefir, kimchi and live yogurt led to increased microbial diversity, which was associated with lowered markers of inflammation. While more research is warranted, consuming these foods (which all happen to be pretty cheap, especially if you make them at home) seems to be an easy way to contribute to your overall physical and mental wellbeing.
Limit highly processed foods, sugary drinks and alcohol
I generally take an inclusive approach to food; however, there are some dietary patterns and habits that are associated with poorer brain and mental health outcomes.
The flip side of the data showing that a healthy, whole-food diet is associated with better mood is that a Western-style diet – high in added sugars, refined carbohydrates, processed meat, fried/fast foods and saturated fats – is associated with an increased depression risk in adults and more inflammation and depression in adolescents. There is also evidence that a Western-style diet can impair memory function and appetite control within just a week.
Adolescents are prime consumers of sugar-sweetened soft drink, which is of concern in light of research showing that, within just three weeks, moderate consumption of these products increased markers of inflammation in otherwise healthy young men. Trying to reduce or limit your intake of sugar-sweetened beverages is probably a good idea.
Alcoholic beverages can, in excess, be detrimental to mood, and research indicates a relationship between excessive alcohol consumption and major depression. Try to stay within or below national recommendations for healthy consumption. If you struggle to control your alcohol intake, contact your GP to find out about support services in your area.
How much do supplements help?
You might be wondering whether there isn’t an easier way to benefit from the impact of nutrients on mental health. Couldn’t I just take a pill? Certainly, dietary supplements are extremely popular. For example, 48 per cent of British adults regularly take a multivitamin or dietary supplement. And this translates to a lot of money: for 2020, the global dietary supplements market was estimated at a whopping $170 billion. But what good, if any, do supplements do?
Research suggests that, in the context of an overall healthy diet, there are limits to the health benefits of supplementation. In addition, scientists have isolated only a fraction of the beneficial compounds found in plants, meaning that there is unlikely to be a man-made supplement that can do for us what whole foods can. Therefore, for most of us, it would be best to try to increase our consumption of plant foods, wholegrains and oily fish. However, there might be a role for the targeted use of supplements to help protect brain health and support mood.
As discussed, vegans and vegetarians are likely to benefit from a supplement that provides pre-formed DHA and EPA. Most vegans are aware of the need to supplement with Vitamin B12, a nutrient that is found predominantly in animal foods and is essential for healthy brain function. The symptoms of B12 deficiency include headaches, fatigue, depression and memory problems. In fact, in severe cases, B12 deficiency can mimic dementia.
A 2019 meta-analysis found evidence of a potential beneficial effect of B vitamins on stress. Similarly, research led by the clinical psychologist Julia Rucklidge in New Zealand suggests that broad-spectrum micronutrients (vitamins and minerals) might support recovery from acute stress. In this case, supplementation may be beneficial for those with a poor nutritional intake, those with poor mood and/or those going through an acutely stressful period.
The question of whether Vitamin D can improve depression has haunted the research literature. Recent meta-analyses indicate that improved Vitamin D status is associated with reduced depression risk. It could be that any possible benefit of the vitamin for mood is linked to its ability to mitigate inflammation. However, more research is needed for the depression results to be considered robust. That said, it is also true that there is widespread Vitamin D deficiency in the general population, particularly in people with darker skin living at high latitudes and during the winter. Supplementation for these groups is generally advisable.
The book Brain Changer (2019) by Felice Jacka, professor of nutritional psychiatry at Deakin University in Australia – who led the groundbreaking SMILES trial mentioned above – outlines the research on brain health and food, and provides recipes to help readers introduce more whole foods into their diets.
Also at Deakin, the Food and Mood Centre offers a free three-week course, through Future Learn, on how to use food to improve mood.
The TEDx talk ‘The Surprisingly Dramatic Role of Nutrition in Mental Health’ (2014) from the clinical psychologist Julia Rucklidge gives an overview of some of the evidence on the use of nutritional supplementation in the treatment of psychological distress.
The book The Better Brain (2021), co-written by Rucklidge with the research psychologist Bonnie Kaplan, provides a comprehensive review of the use of supplemental micronutrients in conditions such as ADHD, anxiety and depression.
The book The Psychobiotic Revolution (2017) by John Cryan and Ted Dinan – experts in microbiome research and specifically ‘psychobiotics’ (the influence of the gut microbiota on brain development, structure and mental illness) – and the science journalist Scott C Anderson explains how and why microbes improve common mental health conditions.