The World Health Organization (WHO) has defined mental health as “a state of well-being in which the individual realizes his or her own abilities can cope with the normal stresses of life can work productively and fruitfully, and is able to make a contribution to his or her community” (1). In comparison, mental illnesses are characterized by alterations in thinking, mood or behaviour associated with significant distress and impaired functioning. It is important to understand that mental health and mental illness are not mutually exclusive concepts (i.e. it’s not all or nothing!), which means that somebody without a mental illness can experience poor mental health and vice-versa.
In Canada, it is estimated that 1 in 5 Canadians will suffer from a mental health problem or illness every year and 1 in 2 people will be affected at one point in their lifetime (2). Mental illness doesn’t discriminate in age, education, culture or income levels: anybody can be affected. Mental illness takes many forms, including mood disorders, anxiety disorders, schizophrenia, personality disorders and eating disorders. Mood and anxiety disorders are among the most common mental health problems in Canada, they affect around 3 million adults aged 18 years and older (3).
There are multiple causes to mental health illness, it’s a complex interplay of genetics, biological, personality and environmental factor. We don’t have much control on most of these factors: you can’t erase your family history of depression or the stressful life events you’ve been through. Therefore, some people might be wondering how they can have a positive impact on their mental health through their lifestyle. We eat about three times a day, so is there a way food might help?
Let’s dive deep and discover the relationship between nutrition and mental health!
*However, I’d like to do a little pause here and remind you that with everything happening, we need to have compassion for ourselves. It is a tough time and food should not be an extra stress.*
To start off, before going into how nutrition might have an influence on mental health, it’s important to consider how mental health can impact the way we eat. Mental illnesses, such as major depressive disorder and anxiety disorder, can come with symptoms like fatigue, physical GI symptoms (nausea, abdominal pain, bloating, etc.), anhedonia and change in appetite. Therefore, people living with these diseases are more likely to have less energy and enthusiasm to prepare food, cook and eat. Just think when you come home after a bad day, you might not be in the mood to prepare a delicious 3 course meal, right? For people living with mental health diseases and having to fight these symptoms all day, it is a big challenge and not something to neglect.
Studies have shown a correlation between the severity of depressive symptoms and diet quality. The more chronic and severe the symptoms are, the lower the diet quality is. This is also exacerbating when there is comorbidity (e.g. living with major depressive disorder + substance addiction) (4). Increased sleep time, decreased appetite, anhedonia and mood symptoms are the most associated with poor diet quality (4). Furthermore, other studies have observed that people living with depression tend to have eating behaviours related to emotional and external stimulus and less to biological stimulus, so the “real” hunger (5). This being said, it’s not a one-way street. There are complex interactions between mental health and nutrition.
The Mediterranean diet is characterized by a high intake of vegetables, fruits, whole grains, fish, olive oil and moderate amount of meat, dairy and red wine. The Standard American Diet (also called the “SAD diet”) is basically the opposite: a lot of processed food, and minimal amount of whole food such as fruits and vegetables. While we have a lot of data indicating that the Mediterranean diet is associated with reduced mortality, cardiovascular diseases and better health outcomes (15), we might wonder if there’s any effect on mental health as opposed to the SAD diet (maybe a little hint here?)
Results from two meta-analysis looking at the effect of different dietary patterns on depressive outcomes indicate that people with high adherence to the Mediterranean diet have lower risk to develop depression disorder across their lifespan (6). Higher diet quality score in studies have also been linked to reduced risk of depression. However, most of these results come from observational studies, so there are confounder variables that limit the generalization. A randomized controlled trial called the SMILES trial (cute, eh?) investigated the effect of a 12-week intervention with a modified Mediterranean diet on depressive symptoms as opposed to a control group. Results showed a significant reduction in the severity of depressive symptoms in the dietary intervention group. While there are still limitations, these are promising results that open more doors to investigate the effect of diet quality on mental health outcomes for people living with mood disorders (7).
On the other side, high consumption of processed food, highly predominant in the Standard American Diet, has been linked to an increased risk of depression 5 years later in cohort studies (8). The SAD is also associated with several other chronic diseases, such as diabetes, cancer and cardiovascular diseases (9).
Vegetarianism and veganism have gained a lot of interest in the past years. Many studies have reported a beneficial effect on inflammatory markers, glucose, insulin and plasma lipids with a plant-based diet compared to animals based (10). However, the effect on mental health isn’t so clear. A systematic review from 2019 examined the effect of a plant-based diet on the body and the brain and results are conflicting. Two studies in healthy adults on a plant-based diet showed improvement in depression, anxiety, stress and depressive symptom scores (11, 13), but a recent large cross-sectional study indicated a higher occurrence of depressive symptoms for people on a vegetarian diet compared to non-vegetarians (12). As you might see, right now, there’s not enough studies on that topic, they are only observational and results are inconclusive to state if a plant-based or animal-based diet can have a positive effect on mental health (10). More research, especially clinical trials, will allow us to have a better idea if an omnivore or plant-based diet can be more beneficial for mental health.
Studying the effect of a specific dietary pattern on mental health is already really hard to achieve, so even more for any specific food. Our whole food pattern has much more impact all together than a single nutrient. However, research has looked had the effect of some nutrients or supplements as an adjunct therapy. There are some preliminary data for omega-3, vitamin D, folate and N-acetylcysteine.
Omega-3 fatty acid supplements, with high-EPA formulas, are likely to small-to-moderate positive effect on major depressive disorder in combination with pharmacotherapy. No beneficial effect has been found when the supplement has mainly DHA and when the depressive disorder is accompanied by other health issues.
For vitamin D, moderate improvements in major depression have been observed with supplementation. However, these results come from clinical trials from China and Iran, where there’s more sunlight than in North America. Vitamin D levels are largely influenced by sunlight exposure, so clinical trials in other settings are required to confirm these findings.
For folate (vitamin B9) and N-acetylcysteine, small overall benefits and moderate reduction in depressive symptoms have been seen in randomized controlled trial (14). More data is needed to indicate the use of any of these supplements for mental health, so always consult your health care provider before starting any on your own, especially if you’re taking medications.
So, why are we seeing these results with different dietary patterns? Many different hypotheses are in the game. The gut-brain-axis is one largely studied right now and I can’t wait to see what research will show in the next years. For more information, see my two articles here on the gut microbiome and the gut-brain-axis. Inflammation is also an underlying possible mechanism related to diet and mental illness(16). Epigenetic, which is the influence of the environment on the expression of our genes, might also be involved (17).
I can’t stress this enough: your diet won’t fix your mental illnesses. These are serious conditions that require the help of a team of health professionals. So please, if somebody tells you to change your whole diet in order to heal from your depression or anything else, RUN. To this date, having a balanced and diversified diet rich in vegetables, fruits, whole grains and unprocessed food, such as the Mediterranean diet, seems to be your best option. Not only for your mental health, but for your overall health too!
Also, remember that food is not only about nutrients and physiological reactions in our body, food is also pleasure, cultural, memories, connection, love and delicious! Having a delicious burger with your family can bring you an unconditional moment of pleasure, so enjoy it. If you become obsessive about food and stress about everything you put into your mouth, I would argue that your mental health is suffering!
Food should not be an extra stress in your life. If you are ready to heal your relationship with food and your body, check out my online program!
The Balanced Practice is a team of professionals specialized in eating disorder outpatient treatment. We strive to provide evidence based nutrition counselling to support you, or your loved one, in achieving full recovery. Schedule a connection call now.
Marie-Pier Pitre-D’Iorio, RD, B.Sc.Psychology
Lead Registered Dietitian at The Balanced Practice
This amazing article was written by Myriam Beaudry,RD . Thank you so much for this great read!