It is well known that daily meals are important for physical health, but in recent years, it has become clear that diet also affects mental health. Research results are being published one after another that show that an unbalanced diet is also associated with the risk of mental illnesses such as depression. We spoke to Professor Hiroshi Kunugi, head of the Department of Psychiatry and Neuroscience at Teikyo University School of Medicine, about the relationship between mental health and nutrition.
Why is nutrition important for mental health?
Traditionally, diet has not been given much importance in the field of psychiatry, but since 2000, research has been actively conducted on the importance of diet not only for physical health management but also for mental health.
There are two main problems with modern eating habits, both of which are related to mental health issues. The first is excessive energy intake. In particular, processed foods such as snacks and instant noodles are easy to eat and can be easily purchased at supermarkets and convenience stores, but they are high in sugar and fat, and excessive energy intake can lead to obesity, metabolic syndrome, diabetes, and other conditions. Research has shown that these conditions are related to the onset of depression . For example, it has been reported that obesity increases the risk of developing depression, and depression increases the risk of developing obesity , and it is known that there is a bidirectional relationship between depression and excessive energy intake.
Another problem is nutrient deficiency. Processed foods and refined foods such as white rice, white bread, and white sugar are delicious and easy to eat, but some of them have important nutrients such as vitamins and minerals removed. Therefore, even though you have excess energy, it is difficult to get enough important nutrients such as vitamins and minerals. It is thought that when you become depressed, you become deficient in neurotransmitters such as serotonin, dopamine, and norepinephrine, and the function of regulating emotions and mood is reduced, making it difficult to feel positive. Nutrients taken in from food are necessary as factors that help produce neurotransmitters as well as raw materials for neurotransmitters. When you are undernourished, you are unable to produce enough of these neurotransmitters necessary for living a vibrant life.
It is believed that avoiding excessive energy intake while also consuming sufficient amounts of the nutrients necessary for mental health can help prevent mental illness.
Nutrients related to mental health
We will introduce nutrients that have been pointed out as being related to mental health, including depression.
(1) Vitamins
Folic acid is a vitamin that has been linked to depression and is particularly prone to deficiency. Folic acid is a nutrient involved in the synthesis of neurotransmitters. Research has shown that folic acid deficiency is more prevalent in patients with depression compared to healthy people .
Vitamin D is also an important nutrient for brain function, and has been reported to be associated with depression . Vitamin D is produced in the body when exposed to ultraviolet rays, so it is important to not only ingest it from food, but also to get plenty of sunlight.
(2) Minerals such as iron and zinc
Iron is a nutrient necessary for the normal functioning of neurotransmitters, and it has been found that iron deficiency increases the risk of depression. A large-scale study found a significant association between iron deficiency anemia and depression and stress symptoms . It has also been reported that zinc and magnesium deficiencies are associated with the risk of depression.
(3) Essential amino acids
Essential amino acids are also important as raw materials for neurotransmitters. Essential amino acids cannot be produced in the body, so they must be ingested through the diet. For example, tryptophan, the raw material for serotonin, is an essential amino acid. It has been reported that blood tryptophan concentrations are lower in patients with depression than in healthy people .
(4) EPA, DHA
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are n-3 (omega-3) fatty acids found in large amounts in fish. Numerous reports have shown a link between EPA, DHA and depression.
For example, an epidemiological study in Finland reported that people who eat a lot of fish have a lower incidence of depression than those who do not.
It is also important to avoid late-night snacks and eat breakfast instead.
To maintain mental health, it is important to eat a balanced diet of foods containing the nutrients mentioned above, while avoiding processed foods as much as possible, which tend to provide too much energy. Traditional Japanese cuisine contains a lot of fish and soy products, which are also good for mental health. We recommend eating modest amounts of staple foods and choosing less refined grains (such as brown rice over white rice). However, it is important to note that Japanese cuisine is high in salt and does not allow the intake of dairy products. In addition to trying to reduce salt intake, it is a good idea to supplement with yogurt and milk.
It’s important not only to consider what you eat, but also to eat regularly. Eat a proper breakfast to get your daily rhythm in order. Survey results have shown that people who eat breakfast are less likely to have a history of depression. Also, try to avoid eating late at night so that you wake up feeling hungry in the morning. Eating late can lead to staying up late and becoming obese. Try to have an early dinner and go to bed early.