Scientific research suggests that some vegetables, fruits and spices can affect the chemistry of the brain and act as mood enhancers, promoting calmness and a sense of well-being, while vitamin and mineral deficiencies can lead to mood swings, insomnia and depression.

"The food that we eat every day has a massive influence on the functioning of the brain," says Tanushree Podder, author of You Are What You Eat.

"Diets with low nutrients, exposure to the environmental toxins in our everyday living, stress, working around the clock against the dictates of our body clock, constant intake of stimulants like alcohol, tobacco, caffeine and junk foods to keep us going, all have an enormous effect on our mental functions," says Ms Podder, who quit the corporate sector eight years after completing her MBA.

"Research has proved that certain kinds of foods play a very significant role in keeping brain cells active," she says.

Brain chemicals (neurotransmitters such as serotonin, dopamine and acetylcholine) influence the way we think and feel and can be affected by what we've eaten, according to Mind, the British-based National Association for Mental Health.

"Low levels of vitamins, minerals and essential fatty acids have been demonstrated to affect mental health and there can be abnormal reactions to artificial chemicals in foods, such as artificial colours and flavours," says Mind.

"There is now a huge amount of evidence linking omega-3 deficiency and depression," psychiatrist Dr Jonathan Zeuss tells Gary Null ("the new Mister Natural", according to Time magazine) in Null's bestseller, The Food-Mood Connection.

"They are absolutely crucial fatty acids.  Your body can't make them itself so it's essential to get them into your diet," says Zeuss, who completed his medical training in Adelaide and practises in Arizona.

Omega-3s are found in green leafy plants like spinach, in fish, chia seeds, flaxseed (also known as linseed) and supplements such as flaxseed oil and fish oil.

"High quality omega-3s provide one of the most powerful and sustainable boosts to healthy moods," says Mike Adams, co-founder of NaturalNews.com.

"You really can eat your way to happiness," says Adams. "By 'happiness', I mean lasting happiness, not the fleeting kind of sensory happiness that might be experienced from sucking the cream filling out of a Twinkie."

"Focus on consuming large quantities of fresh fruit and vegetables," he says. "You simply cannot overeat fresh fruits and vegetables and they're loaded with mood-lifting nutrients. Nuts including pecans, almonds, pistachios, macadamias and walnuts also support healthy moods and healthy brain function."

B group vitamins including B1, B3, B6 and B9 - found mainly in whole grains, nuts and green vegetables - can also positively affect mood, according to studies.

B1 (thiamine) deficiency can lead to decreased mental energy, causing fatigue and depression.  Thiamine-rich foods include wholegrain oats, flax and sunflower seeds, brown rice, asparagus, kale, cauliflower, oranges, potatoes and brewer's yeast.

B3, or niacin, found in legumes, nuts, grains, fruits and vegetables, has been shown to reduce depression and anxiety.

B6, found in bananas, wheat germ, pulses, brown rice and brewer's yeast, can promote mental alertness.

B9, or folate (its synthetic form, folic acid, is found in supplements and fortified foods) supports a healthy nervous system and alleviates insomnia and agitation, says Null.  Foods rich in folate include spinach, broccoli, asparagus, mushrooms, grains, beans and peas.

B12 helps neurological functions including concentration and memory, according to research, but is a common deficiency, especially in the elderly.  It is found in meat, fish, eggs and milk products but is generally not present in plant foods, requiring vegans to take a B12 supplement.

A review published recently in British medical journal The Lancet linked low levels of the mineral selenium with cognitive decline and poor immune function.  Brazil nuts are the richest known source of selenium, which is also found in sunflower seeds, grains (brown rice, wheat germ, oats), fish and shellfish.

Bananas, spinach and the spice cardamom are packed with magnesium, which reduces anxiety and can improve mood.

"Deficiency of magnesium and the response to stress are intimately linked," says nutritionist and homeopath Dr Shewta Shah, "but eating one banana as a mid-morning snack fuels the body with enough magnesium for the entire day."

Complex carbohydrates such as oats, brown rice, potatoes and starchy vegetables have been shown to encourage production of the key neurotransmitter serotonin - also known as "the happy hormone" - which affects mood and behaviour.

In her e-book The Serotonin Secret, Dr Caroline Longmore says low serotonin levels are associated with mood disorders, anxiety and irritable bowel syndrome.

Vitamin D - a hormone, despite its name - can improve mood and memory by enhancing production of serotonin.  A study presented on June 30 to the Endocrine Society's 94th annual meeting in Houston has shown that treatment for Vitamin D deficiency considerably improved women's depression in moderate and even severe cases.

The clinically depressed women who participated in the study received treatment for their vitamin D deficiency without changing any of their antidepressant medication regimes. The authors concluded that boosting vitamin D alone might have beneficial effects on depression.

Vitamin D is found in oily fish, almond milk, coconut milk and mushrooms.

Our bodies also produce vitamin D when exposed to the sun. The Cancer Council of Australia recommends that during winter in the southern parts of Australia, where UV radiation levels are less intense, people may need about two or three hours of sunlight a week to maintain adequate vitamin D levels.

* The Department of Health and Ageing says more than 13.6 million scripts costing $333 million were written in 2010-11 for antidepressants subsidised by the Pharmaceutical Benefits Scheme. The data showed that women were twice as likely as men to take antidepressant prescription pills.