What you eat can help to boost your mental well-being, even if you do not sense any immediate effects.
Experts say that consuming sufficient amounts of specific nutrients can stimulate the brain and other parts of the body which, in turn, help to maintain mental health.
For instance, studies have shown that vitamin D and folic acid help deal with depression.
Vitamin D is produced when the skin is exposed to the sun's ultraviolet rays. In regions where sunshine is limited in winter, more people tend to suffer from depression.
"The theory that a shortage of vitamin D is related to depression is widely supported," said Dr Hiroshi Kunugi, director of the department of mental disorder research at the National Centre of Neurology and Psychiatry in Japan.
"It is believed that vitamin D improves the functions of neural transmitter substances inside the brain and works to protect it."
Foods that are rich in vitamin D include mushrooms and seafood.
Meanwhile, folic acid is also noted for helping to prevent and treat depression.
A lack of folic acid is known to cause ailments such as anaemia and is believed to increase the risk of depression. It is also related to neural transmitter substances.
According to researchers, the level of folic acid in the blood of people with depression tends to be lower than that of healthy people.
Some folic acid-rich options include liver and natto.
Iron is also essential for maintaining mental health. Iron is vital for producing haemoglobin, which transports oxygen in the blood.
If there is not enough iron, less oxygen is carried around the body, causing iron-deficiency anaemia.
Brain function may be affected too, as the lack of iron can cause a syndrome in which sufferers feel pain, itching and discomfort in their legs whenever they lie down.
Some people experience sleep disorders due to these symptoms. Others develop symptoms similar to depression, such as frustration, lack of concentration and loss of interest or attention.
Liver, red meat and fish contain a lot of iron. But women tend to suffer from an iron deficiency when they menstruate.
Some cases of postpartum depression, in which women develop symptoms such as depression after childbirth, are believed to be related to a shortage of iron.
"Postpartum depression is caused by changes in hormone balance, as well as environmental and other factors," said Dr Kunugi.
"An iron deficiency is assumed to be one of them. There aren't many cases in which an increase of iron totally cures postpartum depression, but it is worthwhile taking a blood test to check it out."
However, it is important to note that consuming too much iron will adversely affect the internal organs. A blood test is useful to determine the proper iron intake level.
There is also a theory that the brain and intestines affect each other.
Irritable bowel syndrome shows that mental stress affects the intestines. It has been reported that sufferers develop symptoms such as abdominal pains when facing stressful situations, such as boarding an overcrowded train.
"There's a report saying that inside the intestines of patients with irritable bowel syndrome, beneficial bacteria such as bifidus have decreased, or detrimental bacteria such as clostridium have increased," Dr Kunugi said.
"If the intestinal bacterial imbalance worsens, abdominal pains and other symptoms will occur more often. With increasing stress, the intestinal bacterial balance will deteriorate further. Patients could fall into a vicious circle."