Depression levels are at an all-time high. Among people aged 15 to 45, depressive disorders are the leading cause of disability worldwide. In 2020, depression will for the first time be the top cause of disability in the US.
Not until relatively recently has serious, systematic clinical attention been paid to the role of diet in mental health in terms of prevention, causation, and treatment. Now, there is such recognition of the importance of diet for mental health that a new field of medicine has arisen: nutritional psychiatry.
An overview of this emerging field, published in November 2019 by the European College of Neuropsychopharmacology, noted: “While the determining factors of mental health are complex, increasing evidence indicates a strong association between a poor diet and the exacerbation of mood disorders, including anxiety and depression, as well as other neuropsychiatric conditions.”1
While neuropsychiatric conditions are multifaceted, and factors such as genes and early life trauma are not readily altered or offset, diet is something we can address — with, as it turns out, often very significant results.
We’re still learning about the many ways that nutrition has an impact on mental well-being, but substantial research in nutritional psychiatry strongly suggests that the microbiome–gut–brain axis is extremely relevant for an individual’s brain development, emotions, and behavior. The authors of a 2015 review titled “The Gut Microbiome and Psychiatry” concluded: “The recognition that the gut microbiota interacts bidirectionally with other environmental risk factors, such as diet and stress, suggests promise in the development of interventions targeting the gut microbiota for the prevention and treatment of common mental health disorders.”2
What are some of the ways a healthy microbiome and good nutrition may affect mental well-being? Combating free radicals, lowering oxidative stress, reducing inflammation, bolstering the immune system, and boosting serotonin levels are a few, and all of these can be heavily influenced by what we put in our mouths.
Inflammation is the immune system’s normal response to tissue injury of any kind, including trauma, heat, toxins, and infectious agents. Currently, some research on depression is looking at its association with inflammation in the brain, and how the immune system may play a role in the development of stress and depressive symptoms.
Cytokines have drawn interest as indicators of high inflammation levels. Consistently, researchers are finding that people who experience major depressive disorders have high cytokine levels in their blood.
How do bacteria fit in here? We now know that the billions of “good” bacteria in the gut’s microbiota limit inflammation, as well as protecting the intestinal lining in its vital role as a barrier against toxins, and activating neural paths that allow direct communication between brain and gut. Researchers are also finding evidence that these bacteria’s effects extend beyond the gut, reducing inflammation levels elsewhere in the body.
It’s widely understood that neurotransmitters play a major role in our mood. The best known of these, serotonin, assists with regulating mood, sleep, and appetite and reducing pain. Remarkably, 95% of a person’s serotonin is produced in their GI tract, which contains approximately a hundred million neurons. It’s now known that serotonin production is highly affected by gut bacteria, as is the functioning of these intestinal neurons.
It makes sense that our gut health has a tremendous effect on what gets transmitted to our brains, influencing our emotions and mental well-being. Given all this, how can we reassess our diets to give ourselves a better chance of preventing or combating depression?
Several systematic reviews and meta-analyses of the research point to a number of promising approaches. A 2013 article in the American Journal of Clinical Nutrition reported that diets high in fruit, vegetables, whole grains, and fish may lower an adult’s risk of depression.3 Another meta-analysis published that same year found that following the “Mediterranean diet” — rich in plant foods and lean meat such as wild salmon — might reduce the risk of depression by 30%.4 A 2017 meta-analysis of 21 studies from 10 countries concluded: “A dietary pattern characterized by a high intake of fruit, vegetables, gluten free whole grains, fish, olive oil, low-fat dairy and antioxidants and low intakes of animal foods was apparently associated with a decreased risk of depression. A dietary pattern characterized by a high consumption of red and/or processed meat, refined grains, sweets, high-fat dairy products, butter, potatoes and high-fat gravy, and low intakes of fruits and vegetables is associated with an increased risk of depression.”5
Rising anxiety and depression rates among the very young also make the possibility of dietary interventions very important. A 2014 systematic review of the relationship between diet and mental health in children and adolescents found that higher intakes of foods with saturated fat, refined carbohydrates, and processed food products were associated with poorer mental health.6
In 2017, a large randomized controlled trial found that what you eat could help treat or prevent brain-based disorders, especially depression. Researchers here identified “significant reductions in depression symptoms” from dietary interventions, independent of other factors, including smoking rates and physical activity.7
These associations between diet and depression are independent of other confounding factors such as education, income, body weight and other health behaviors.
Researchers caution that much more study is needed to establish and understand connections between nutrition and mental health. In the meantime, though, you might wish to explore several different ways that diet can be adjusted to potentially reduce the risk of depression and assist in treating it.
One simple thing to examine is sugar consumption. It’s now known that diets high in refined sugars make insulin regulation more difficult and harm the brain by promoting inflammation and oxidative stress. A 2015 article published by the Harvard Medical School noted that “multiple studies have shown a correlation between a diet high in refined sugars and impaired brain function and a worsening of symptoms of mood disorders, such as depression.”8
Let’s get back to those gut bacteria, because they’re of course profoundly affected by what we feed ourselves. It’s now known that the more diverse the plant foods in your diet, the more diverse your gut microbiota, so the healthier, stronger, and more robust your gut will be. The types of fats you eat are also important. Short-chain fatty acids are good for our gut, and they affect gene activity, metabolism, and body weight; they also profoundly influence our immune system, which in turn affects our risk for depression.
Omega-3 fatty acids are important too. A 2017 study found a correlation between omega-3 consumption and more beneficial gut microbiome composition.9 Notably, a recent review article for lay readers observed that “many studies point to the power of omega-3 fatty acids in the diet to improve symptoms of anxiety and depression and even play a role in the prevention of suicide,“ citing several peer-reviewed research publications.10
Polyphenols also play a key role for the gut and its bacteria, and they may assist in preventing depression. Excellent sources include berries, beans, dark chocolate, black and green teas and hazelnuts.
While numerous foods such as these can improve the gut environment for existing bacteria, you can also add beneficial bacteria to your gut in the form of probiotics. These are found in cultured and fermented foods, such as yogurt, kefir, sauerkraut, and kimchi. Interestingly, multiple studies suggest that probiotics can help improve symptoms of anxiety and mood disorders in people with clinically diagnosed disorders, as well as those who are otherwise healthy but experience some of the symptoms of mental health conditions.
Bacteria need their own foods too, called “prebiotics.” These are forms of dietary fiber digestible by our gut bacteria but not by us. They’re found in numerous fruits and vegetables, which handily also contain many other nutrients beneficial for our physical and mental health.
Consult your physician who practices functional medicine, about making dietary adjustments to help your mental health. Work together to identify the root cause and then address your nutrient imbalances. Your physician can order the correct lab tests to check nutritional deficiencies such as iron, magnesium, potassium, selenium, and zinc, as well as the B vitamins (particularly thiamine, folate, B6, and B12) and vitamins A, C, and D. It’s also essential to eliminate gastrointestinal issues such as irritable bowel syndrome, small-intestine bacterial overgrowth (SIBO), intestinal permeability, hormonal imbalances, and food allergies. Having an allergy to one or more foods can lead to a metabolic disorder that cascades into a whole host of symptoms, including “brain fog” and depression. Gluten and dairy are very common allergens. Interestingly, partially digested wheat and dairy particles called gliadorphins and casomorphins are found in the urine of severely depressed patients. Eating more organic, nutrient-dense leafy and cruciferous vegetables is one of the few ways that research suggests we can protect ourselves against depression.
Further illuminating research in the area of nutritional psychiatry will no doubt be forthcoming. Stay tuned, and don’t forget to incorporate other behaviors known to support good mental health: regular physical activity, good and sufficient sleep, time in nature, and a healthy work–life balance.