An increasing number of us experience poor mental health at some stage in life: currently it's estimated that around 1 in 8 people worldwide have a mental disorder, although actual numbers may be higher, as this only represents those with a formal diagnosis. Mental disorders such as depression can impact a person's ability to participate in daily life, at school or work, and can affect relationships with others. Nutritional psychiatry is a fast-growing field of research, and researchers have found associations between diet and risk of developing common mental disorders such as depression and anxiety. Although changing your diet won't necessarily cure a mental disorder, healthier lifestyle changes (including diet) have been shown to improve symptoms. Trials have found that a healthier diet can decrease symptoms of depression and anxiety, while an unhealthy diet high in ultra-processed foods may increase risk factors for developing a mental disorder.
Risk Factors For Mental Disorders
Research in this field is still fairly new, so there's a lot that isn't yet fully understood, however there is already good evidence linking certain dietary patterns, foods and nutrients with improved mental health. Several risk factors associated with lifestyle diseases are also believed to play a central role in mental disorders, including stress, diet, and chronic low-grade inflammation. Lifestyle diseases and mental disorders are also commonly seen in the same person, and a person with obesity has up to a 53% higher chance of developing depression.
A diet high in ultra-processed foods can promote chronic low-grade inflammation and may negatively impact proteins that support creation of new nerve cells in the brain. Dietary patterns that include plenty of plants and minimally-processed foods, such as the Mediterranean diet, have shown beneficial effects for both lifestyle diseases and mental health. A diet rich in plant foods can influence gut microbiota composition and functions carried out by gut microbes, such as production of neurotransmitters, and can also contribute nutrients required to make some of these useful substances.
The Gut - Microbiota - Brain Axis
Your gut and brain communicate with each other via the 'gut-microbiota-brain (GMB) axis'. This involves several biological systems including the enteric nervous system (ENS) and vagus nerve, the neuroendocrine system, the hypothalamic-pituitary-adrenal (HPA) axis, and the immune system. Communication is also bi-directional: your gut can send signals to your brain, and your brain can send signals to your gut. Your gut microbiota (GM) also produce substances that communicate with your brain including neurotransmitters (GABA, noradrenalin, dopamine and serotonin), amino acids (tyramine and tryptophan), and short-chain fatty acids. What we eat, especially fibre and bioactive components such as omega-3s and polyphenols, can alter the GM and can promote production of these important substances.
The Enteric Nervous System is your gastrointestinal tract's own nervous system which regulates several digestive functions including muscle movement, production of digestive enzymes, and blood flow for nutrient absorption and elimination. The ENS also communicates with your brain and can regulate mood.
The Hypothalamic-Pituitary-Adrenal Axis regulates your stress response, production of stress hormones (adrenalin and cortisol), and automatic functions such as digestion. The HPA axis can also down-regulate digestive functions when you're stressed, which is how stress, anxiety and depression may impact gut function and worsen gut symptoms, particularly in those with Irritable Bowel Syndrome.
Mental Health and the Mediterranean Diet
The SMILES study was the first randomised, controlled study which trialled dietary changes as an intervention to improve symptoms of mental disorders. Researchers found that a modified Mediterranean diet including 60ml olive oil and 30g nuts per day improved symptoms of depression in 32% of participants after just 12 weeks. Another trial, HELFIMED, also found positive effects when participants ate a Mediterranean diet and took fish oil supplements containing 100mg EPA og 900mg DHA (omega-3 fatty acids), reporting reduced anxiety and stress in participants that showed increased blood levels of EPA.
Some key foods and nutrients in the Mediterranean diet for mental health:
🐟 Polyunsaturated fatty acids, especially EPA and DHA (found in oily fish or algae) may reduce inflammation and support brain health, structure and function
🫐 Antioxidants and polyphenols (from fruit, vegetables and other plant foods) may help reduce inflammation, oxidative stress, and help reduce cortisol
🥜 Fibre (from fruit, vegetables, legumes, nuts, seeds, herbs, spices) can modify gut microbiota, which can increase production of anti-inflammatory substances, neurotransmitters and other beneficial substances
Ultra-Processed Foods and Mental Health
Ultra-processed foods (UPFs) are also associated with negative effects on mental health, and reducing your intake of these foods may help improve mood and mental health. UPFs are normally processed using methods that we wouldn't normally use at home, which changes the structure of the ingredients and affects how it behaves in your body.
When cells in foods from plants are crushed during processing, nutrients contained in these cells are more easily absorbed during digestion, which can promote a more rapid and higher blood glucose response, followed also by a rapid decrease in blood sugar. UPFs also tend to contain high amounts of added sugars which also add to this effect. UPFs generally contain minimal fibre, and due to processing of the ingredients your body doesn't need to work break down food molecules, meaning that UPFs also don't tend to keep you feeling full for long periods. UPFs are generally low in many of the nutrients associated with reduced risk of mental disorders. They also tend to be high in added sugars, trans fats and salt, which contribute to inflammation, increasing risk for mental disorders. .
What can you do to help improve your mental health?
🥗 Eat a nutritious diet that includes plenty of plants (fruit, vegetables, legumes, nuts, seeds). Aim for at least 30 different types to help increase diversity in your gut microbiota.
Key features of the Mediterranean-style dietary patterns that have been associated with improved mental health also include healthy fats from sources such as olive oil, oily fish and nuts.
Plant foods such as citrus fruit, berries, broccoli and hazelnuts are also sources of flavonoids, a type of polyphenol which has been associated with reduced risk of depression. Polyphenols may also have positive effects on the gut microbiota.
🧄 Prebiotic and probiotic foods may also help. Current research is underway to investigate direct effects of prebiotics and probiotics on mental disorders, so we don't yet have enough evidence to confirm an effect just yet. But we know that prebiotics and probiotics can positively modify gut microbiota, so may also improve production of substances that are involved in gut-brain communication.
Include physical activity in your daily routine. Aim for at least 30 minutes of moderate intensity physical activity per day (adults). Restorative activities such as yoga, meditation, and breath exercises can also positively affect mood and mental health.
Get enough sleep. Lack of sleep can impact mood directly, but can also negatively impact your gut microbiota, and your food choices. Aim to go to bed at an appropriate time, "switch off” from technology at least 1 hour before to prepare for sleep, and reduce or omit caffeine if you notice this impacts your sleep.
Spend time with others. Several trials of diet and mental health also saw positive effects in the non-intervention group, which only received social support, showing that this is also important for mental wellbeing. The social aspect of food (sharing and connecting with others, or "conviviality") is also specifically included on the Mediterranean Diet pyramid.