Does what you eat impact your mental health? Or do people eat an unhealthy diet because their mental health is impaired? And what is the chemical link between diet and mental health? These are fascinating questions that have been tackled in a growing body of research that tends to point to the conclusion that your diet can directly impact your mental health.
Several recent meta analyses, which combine the results of multiple scientific studies, support the conclusion that there is a link between diet and risk of depression. Specifically, one study concluded:
“A dietary pattern characterized by a high intake of fruit, vegetables, whole grain, 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.”
Another meta-analysis combined only prospective studies that reported on exposure to dietary patterns or food groups and the incidence of depression or depressive symptoms. This meant that they looked at a baseline diet and then calculated the risk of study volunteers developing depression in the future. The study found that “adherence to a high-quality diet, regardless of type (i.e., healthy/prudent or Mediterranean), was associated with a lower risk of depressive symptoms over time.”
It is not exactly understood yet from a chemical perspective why a healthier diet leads to better mental health. One chemical that experts often cite as important in this area of research is serotonin. Serotonin is an important neurotransmitter, a chemical that transmits messages between nerve cells, in the human body. It is believed that serotonin helps to regulate mood and social behavior, appetite and digestion, sleep, memory, sexual desire, and function.
A key theory in the cause of depression in the last 50 years is that it may involve an imbalance of neurotransmitters or hormones in the body. One neurotransmitter which has been used as a treatment is serotonin. Normally, once a neurotransmitter has transmitted its neural impulse it is reabsorbed into the body. SSRIs, Selective Serotonin Reuptake Inhibitors, a major category of antidepressants, prevent serotonin from being reabsorbed, leading to higher levels of serotonin in the synapses. However, it is unclear whether low serotonin levels contribute to depression, or if depression causes a fall in serotonin levels.
If low serotonin levels indeed contribute to depression, there are two potential ways in which eating a healthy diet could impact serotonin levels and as such prove the link between diet and depression.
Firstly, tryptophan, which is a precursor, a main ingredient that the body needs to make serotonin, can be found in whole foods such as:
In addition, bananas contain serotonin.
Could a healthy diet that includes whole foods such as eggs, salmon, and bananas be the cause of the diet-depression connection by directly increasing serotonin levels?
Secondly, there’s a potentially more interesting hypothesis, which relates to the fact that approximately 95% of serotonin is produced in the gastrointestinal tract. There is growing support for the idea that gut health can impact mood through the ‘Gut-Brain Connection’, which refers to the bidirectional communication between the central nervous system and the enteric nervous system that connects cognitive and digestive behavior. Experts hypothesize that the production of serotonin is highly influenced by the billions of “good” bacteria that make up the intestinal microbiome.
Could it be that eating a healthy diet means better gut health, more serotonin produced in the gut and therefore improved mood through the Gut-Brain Connection? These are important mental health questions which don’t yet have definitive answers, but which scientists are continuing to research.
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