It will come as no surprise to hear that what we eat can have a big impact on how we feel, mentally as well as physically. After a hectic week, with too much fast food and hastily consumed coffee, or a couple of nights on the make-mine-a-double-and-a-doner diet, we may well feel what we've put into our bodies punishing our mind and mood.
But there are also foods that we might not even be aware of that are having a big impact on how we feel. And this can be more serious than just getting grouchy from overdoing it – there's a wealth of research that suggests that certain types of food actually contain essential components for good mental health, with deficiencies potentially even worsening diagnosable mental disorders such as depression.
Two recent reports have hit headlines with the claim that a Mediterranean diet could protect against depression. With significantly fewer cases of depression in Mediterranean countries, researchers now think it may be the healthy diet, rich in fresh vegetables, whole grains and olive oil, that helps maintain mental health.
While depression is not caused by just one factor, eating well is a positive step in the right direction and in some cases deficiencies of certain vitamins, minerals, amino and fatty acids do seem to directly relate to our emotional wellbeing. "For somebody with mild depression, what they eat can really help. We can very easily keep people on track with good food," says nutritionist Dr Caroline Longmore.
"Diet is one of the important factors for our mental health," says Andrew McCulloch, the chief executive at the Mental Health Foundation. He suggests that the impact of diet on depression has been underestimated but that "there's a lot of research going on now, and in the next 10 or 20 years we'll understand a lot more." In the meantime his advice is to "mix it up". There is no "magic" ingredient or expensive supplement that cures depression, but McCulloch explains that if we eat a balanced, varied diet, we will naturally get all the mood-boosting proteins and fatty acids we need, as well as a full range of micronutrients.
Dr John Briffa also explains that our brains use a lot of energy, and need sustained fuelling from food - "just that one thing can make a difference to people who are prone to depression." He also recommends eating a diet made up of foods as "natural and unprocessed as possible".
This sound advice instinctively makes a lot of sense. But might there be a few easy changes or top foods we should ensure we munch on? Here are some of the diet choices and important ingredients that might help you eat yourself happy.
Follow a Mediterranean diet
We often hear about the physical benefits of eating a Mediterranean diet, but two recent studies concluded it could also have a positive impact on your mood. A diet high in vegetables, fruits, fish, nuts, whole grains and olive oil could stave off depression, according to two separate studies conducted in Spain and London last month.
Spanish scientists from the Universities of Las Palmas and Navarra studied a group of 10,094 individuals over four years, and found that those who followed a classic Mediterranean diet were 30 per cent less likely to develop depression. Researchers from University College, London, who studied 3,486 civil servants over five years, also came up with exactly the same figure: Mediterranean-style eaters were 30 per cent less likely to develop depression. It is thought that while different aspects of the diet may have specific benefits, it may be the combined effect that has a big impact on mood.
"It is plausible that the synergistic combination of a sufficient provision of omega 3 fatty acids together with other natural unsaturated fatty acids and antioxidants from olive oil and nuts, flavonoids and other phytochemicals from fruit and other plant foods and large amounts of natural folates and other B vitamins in the overall Mediterranean dietary pattern may exert a fair degree of protection against depression," said the authors of the Spanish study in Archives of General Psychiatry.
Mediterranean countries are known to have lower levels of depression than those in the north of Europe, and this research suggests that it might be due to their swapping red meat and dairy for fish and olive oil, and ditching processed foods in favour of fresh fruit and veg.
Studies have linked depression with low levels of the mineral selenium. The recommended daily amount is 0.075mg for men, and 0.06mg for women. Professor Steve McGrath, of Rothamsted Research, called last month for small amounts of selenium to be added to fertiliser treating wheat farms to increase our consumption of the mineral. Until a few decades ago, much of our bread was made with imported American wheat grown in soil naturally rich in selenium. Since switching to British flour our intake has declined, as our soil naturally has low levels of selenium, meaning Britons' intake is now only half what it should be.
Dr Margaret Rayman published a paper in 2000 that linked low selenium levels with a "significantly greater incidence of depression and other negative mood states such as anxiety, confusion and hostility". Unrefined grains, cereals, meat, eggs, and even offal are all recommended as ways to increase your intake, but the easiest way to dose-up is to grab a handful of nuts. Brazil nuts are a super selenium source, with 0.02mg – that's a third of a woman's RDA – in each little nut. One of the easiest mood-boosting lifestyle changes you can make, nibbling nuts could turn healthy snacking into happy feeling.
Watch your blood sugar
The low GI diet might sound familiar and faddy – it admittedly did spawn a swathe of cheerily coloured weight-loss cookery books. But there's some sound advice behind it all which can help you balance body and mind. The glycaemic index (GI) is a numerical system that indicates how quickly carbohydrates will make your blood sugar levels rise. And it's these fluctuations in blood sugar which lead to swings in mood and energy.
Choosing foods that are slow to digest, and offer a gradual, sustained release can stop a rollercoaster response, where sugar rushes are followed by energy slumps. Ideal for anyone who just feels food affecting their focus and freshness throughout the day, the GI diet may also be a good place to start for people suffering more serious mental disorders too.
Dr John Briffa reported in his health blog (www.drbriffa.com) in July this year on a study that found links between a high GI diet and depression, with the authors concluding that the "findings suggest a negative effect of an HG [high glycaemic load] weight loss diet on sub-clinical depression". Dr Briffa adds: "The brain generally needs a good steady supply of energy, it can malfunction quite spectacularly if it's underfuelled." Try to choose foods with a low GI: oats and bran cereals, beans, pulses and lentils as well as fruit such as apples and oranges. High GI foods, such as refined white bread, potatoes and sugary treats are best avoided if you want to keep your energy levels – and mental state – on an even keel.
Boost your serotonin
Tryptophan is an essential amino acid which is converted in our bodies into serotonin, a neurotransmitter, or chemical in the brain. "Low levels of the neurotransmitter serotonin are often associated with depression," says Lucinda Bevan, a nutritional therapist for Brain Nutrition (www.brainnutrition.co.uk). Our bodies can't produce tryptophan, so we need to get it through our food. Amino acids are protein fragments, so it is protein-rich foods that can keep your serotonin levels in the happy zone. And the need for serotonin may even explain why we crave carbs – the blood-to-brain absorption of tryptophan is helped by carbohydrates, so those cravings may be our brains crying out for more serotonin.
This means protein and tryptophan-rich foods – such as chicken and turkey, tuna and salmon, beans and seeds – can be most effective when eaten alongside slow-release carbohydrates. "Good-quality protein provides the building blocks for our brain chemicals and can convert in the brain with good quality carbohydrate," says Bevan. Dr Longmore, whose book The Serotonin Secret explores this further, claims that "nine out of 10 people I treat with depression have digestive problems, so they don't produce enough serotonin". She says that improving your diet to include more tryptophan-rich foods, as well an increasing exercise, cutting out caffeine and sugar, and drinking more water, will boost serotonin production – which she claims acts in "exactly the same way as antidepressant drugs".
Get plenty of fish
We hear plenty of stories extolling the benefits of fish oil, claiming that it helps your heart or makes you smarter. But research has also suggested that omega 3, the essential fatty acids found in fish oils, can improve you mood. "Fish consumption has been reported to have an association with better moods and a higher self-reported mental health, even after adjustment for factors such as income, age and other eating patterns," says Dr Deborah Cornah in the Mental Health Foundation's (MHF) "Feeding Minds" 2006 report on the impact of food on mental health. Omega 3 is found in oily fish such as tuna, mackerel and salmon, while vegetarians should try using flax or rapeseed oils and snacking on pumpkin seeds.
Eat up your greens
Several scientific studies have shown links between low levels of B vitamins and psychiatric disorders. The B vitamin folate (better known as folic acid) is thought to be essential for preventing depression. It is also thought that low folate levels may even stop antidepressants from working. "Because folic acid is often deficient in people with depressive symptoms, getting more of this vitamin through foods may help," recommends Dr Cornah in the MHF's report. "The vitamin appears to have the ability to reduce the high levels of homocysteine [an amino acid] associated with depression." Top foods for upping your intake of folic acid include yeast extract, green vegetables (just lightly cooked), and beans and pulses again.
Drink lots of water
It's free, readily available, and incredibly good for us - yet a lot of people just don't glug enough of the clear stuff to keep their minds happy and healthy. Dr Longmore says her very first piece of advice for people suffering depression is to make sure they drink more water. "Not getting enough can cause a chemical imbalance. People should drink at least one-and-a-half litres of water a day," she says. Even mild dehydration can seriously and quickly affect our mood, while day after day of brain-drought is enough to make us "grumpy, irritable and also depressed", according to Bevan. Getting a few more glasses of HO is a simple and easy change to make whether you just want to keep headaches and grouches at bay, or as part of changes in diet to tackle more serious mental health conditions.
What to avoid: False pick-me-ups
* Caffeine, in tea, coffee and fizzy drinks, might give us an energy boost but can also cause a "crash" as the effects wear off. Drinking too much can make you shaky or anxious, and is thought to worsen depression.
* Sweet foods give us a quick fix of that happy feeling (by releasing the neurotransmitter beta-endorphin) and a spike of energy, but it doesn't last. Spending your life on a rollercoaster of sugar highs and lows is bad news for the brain in the long term.
* Alcohol should also be treated with caution. A nice glass of wine at the end of the day might seem like the perfect way to unwind, but it is a depressant, and is likely to exacerbate mental health problems.
* A morning cuppa, an occasional bar of chocolate or the odd pint of lager obviously aren't going to cause depression, but it is worth cutting down – or at least trying not to rely on – stimulating and mood-altering substances.