Revision is seen as the way to get good grades. But eating the right things could be equally vital, says Kate Watson-Smyth

Teenagers up and down the land have started cramming furiously for next month's exams. But as the stress levels mount and the coffee supplies fall, panicking students should realise that results are not entirely down to how much revision they've done.

Increasingly, it is recognised that diet plays a vital role in exam performance. What you eat and when you eat it can make a huge difference to how you do on the day. Lorraine Perretta, a senior nutrition consultant at London's Brain Bio Centre, points out that the brain needs fuel just like any other organ. "Without the correct diet, it cannot give its peak performance," she says. "Eating the right foods can dramatically improve learning, concentration and memory."

The brain uses a quarter of all the carbohydrates you eat under normal conditions, rising to around 40 per cent at times of intense concentration, according to Patrick Holford, author of Optimum Nutrition for the Mind (Piatkus £12.99). "During an exam, your legs don't need the energy as you are sitting down. Your brain uses it all and that's why you are starving at the end of an exam. You would train your body for a physical exam, so why not do the same for a mental test?"

Thinking is a biochemical process, and in order for the brain cells to communicate effectively with each other they need neurotransmitters. These are the messengers that carry information, says Jayne Cormie of The Thinking Business, a company set up to help people improve their thinking skills.

Amino acids are converted into neurotransmitters using vitamins and minerals. Acetylcholine (ACh) is the neurotransmitter responsible for memory, and studies have found that people with Alzheimer's may have less of it. Foods rich in the vitamin complex needed to make ACh include egg yolks, peanuts, liver, broccoli, fish and cheese.

Dopamine, the neurotransmitter involved in motivation and learning, is made from substances found in proteins, nuts and soy, while Serotonin, which is connected to appetite and produces feelings of pleasure, is synthesised from carbohydrates. Within half an hour of eating a carbohydrate-based meal you should feel calmer, hence the importance of a good pre-exam breakfast.

"So many people understand that they need to eat well to maintain a healthy heart or to help their other organs function well, but are astonished by the idea that they need to feed their brains as well," says Cormie. "Food makes a real difference to how well the brain performs."

The brain is 70 per cent water, so drinking plenty is equally important for your memory. Water also improves the brain's function as a whole - when it is dehydrated it works more slowly. This is particularly true of memory; a dehydrated brain releases the stress hormone cortisol, which adversely affects the brain's ability to store information. Too much coffee will also slow down the thinking process and make you feel foggy.

One of the key ingredients for a healthy brain are B vitamins, particularly 6, 12 and folic acid. A new Swedish study has found that you can predict school grades by measuring the levels of a toxic protein called homocysteine in the blood. The higher the level, the lower the grades.

Homocysteine accumulates in the brain when the body is not getting enough B vitamins. Levels can rise in just 24 hours but can equally be stabilised in as short a period of time.

Holford treated one teenager whose homocysteine level was that of a 95-year-old. But in just one month of a diet rich in B vitamins, his level returned to near normal. His memory improved, he was able to focus and no longer complained of being bored. "B vitamins are vital for brain function and are found in fresh fruit and vegetables, and whole foods such as beans. What you eat the night before an exam will have a profound effect," says Holford, who also advises teenagers facing exams to take a strong multi-vitamin and an Omega-3 supplement.

A report published last year by the Soil Association and Business in the Community found that pupils who ate school meals made with fresh ingredients and drank plenty of water had better concentration levels and were calmer and more alert .

The perfect plate of brain food should be one quarter protein, ideally fish, to make you feel alert, one quarter starch, to prevent panic, and half vegetables, for the vitamins and minerals that improve learning and memory.

Holford says: "Students should adopt good habits a month before exams, but even 48 hours in advance will make a difference."

How to feed your brain

BREAKFAST

A good breakfast is vital, and should include lots of slow-release carbohydrates. Refined carbs, like white bread, cakes and sweets, raise blood sugar quickly but it will drop just as quickly, leading to drowsiness and poor concentration.

Blood glucose is the main supply of energy to the brain and you need a steady trickle. Porridge is perfect, but if you don't fancy that, look for wholegrain cereals that are low in sugar and fortified with vital B vitamins. Vitamin B1 raises the brain's ACh levels, which is good for memory.

Eggs provide essential fatty acids (EFAs), which are vital for the formation of synapses in the brain. These, in turn, are involved in the creation and maintenance of memory. The solid part of the brain is mainly made up of fat and needs a supply of these so-called "good fats", as the body cannot produce them itself. Studies have found that people who consume a lot of so-called "bad fats", such as the hydrogenated ones found in ready meals, or a lot of fried and processed fats, actually make the fat in their brains denser, which renders them more dull-witted. "Your brain stops thinking as fast. It becomes less flexible and cannot function as well," says Holford.

LUNCH

Protein makes you feel alert, so if you have an afternoon exam, try a portion of oily fish such as tuna. Tuna, salmon and trout are all rich in DHA, an Omega-3 fatty acid that has been found to be good for brain performance. A study from the Dyscovery Centre, in Wales, found that taking Omega-3 fish oil capsules improved children's concentration by 35 per cent. Rice is also full of those important B vitamins and will help soothe last-minute nerves. A helping of green beans should balance this meal perfectly.

SUPPER

New research has found that a lack of iron leads to reduced brain power. Michael Nelson, of King's College, London, who carried out the study, says: "Too little iron means low haemoglobin levels, which reduces the brain's oxygen supply."

The brain uses about 20 per cent of the oxygen pumping round the body at any one time. "Iron also plays an important role in the transmission of signals in the brain." Red meat is one of the main sources of iron, so vegetarians should make sure they get plenty of dark-green leafy vegetables to compensate. Lentils, beans, nuts and seeds are also good sources. Iron absorption is helped by Vitamin C, a lack of which has also been shown to increase levels of anxiety, so make sure you eat plenty of citrus fruits, tomatoes and peppers with your protein. A slice of hard cheese after supper will provide zinc. Vital for quick thinking, it also helps brain cells transfer information.

HERBS

Sage: In one recent study, those who took sage before a word recall test did much better than those who didn't. This herb, which goes well with pork or can be taken in tincture form, is thought to improve memory by preventing the breakdown of ACh.

Rosemary: This can stimulate the memory, strengthen mental alertness and help fight mental fatigue, a common problem towards the end of exams. Studies have found it can improve long-term memory by up to 15 per cent.

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