Scientists are proving that what's in the foods you eat can affect the chemical composition of your brain - and your mood. That doesn't mean eating jelly turns your brain to mush, or eating meat will make you mean. But nutrition can affect your mood, including your alertness and your perception of pain

What is it about foods that yields this kind of power? It is food's ability to alter the production or release of neurotransmitters, the chemical messengers that carry information from one nerve cell to another. Neurotransmitters are responsible for such important bits of information as 'I'm full', 'Ouch!' or, 'Arrgh! I'm very worried about this!'

The Theory

Just how does a food affect neurotransmitters? According to Dr Richard Wurtman of MIT, who is involved in numerous studies on nutrition and the brain, certain nutrients in foods are precursors to neurotransmitters, and the amount of a precursor nutrient in your diet determines how much of its following neurotransmitter you produce.

Although this may seem fairly straightforward, it is complicated by the fact that foods most often are made up of more than one nutrient, and how those different nutrients interact will also affect the production and release of neurotransmitters.

The Practice

Despite the complexity, if you learn certain established facts, you can affect your mood through diet.

Boost your alertness with protein
Protein foods are broken down into their amino acid building blocks during digestion. One amino acid - tyrosine - increases the production of dopamine, norepinephrine and epinephrine. These neurotransmitters are known for their ability to increase levels of alertness and energy.

No one eats pure tyrosine, but eating foods high in protein will give you a slight mental boost. High protein foods include fish, poultry, meat and eggs. If you can't eat those, try high-protein foods that also contain significant amounts of carbohydrates, such as legumes, cheese, milk or tofu.

For relaxation and stress relief, eat carbohydrates
Carbohydrates will trigger the release of insulin into the blood stream. Insulin clears all the amino acids from the blood, except tryptophan, which normally is crowded out by other amino acids in its attempt to cross the blood-brain barrier.

But when its competitors are out of the way, it floods the brain, where it's converted to serotonin. Serotonin is a neurotransmitter that reduces pain, decreases appetite, produces a sense of calm and, in large quantity, induces sleep. Research has shown that dieters tend to become depressed about two weeks into a diet, about the time their serotonin levels have dropped due to decreased carbohydrate intake.

Healthy carbohydrate foods to turn to for stress relief include wholegrain breads and crackers, wholegrain pasta, rice, cereal and fruit.

For the most beneficial effects of carbohydrates and protein, eat them separately
For example, the energy-boosting effect of protein will be offset if you start out a lunch of fish (pure protein) with a roll (mostly carbohydrate). Eat protein first, then go lightly on the carbohydrate if want to stay alert.

Caffeine can be an effective antidepressant
Despite its bad rap, caffeine can do some good. For mild cases of depression which don't need medical attention, a little caffeine can be an effective antidepressant. It has the added benefit of remaining effective without an ever-increasing dosage daily to achieve the same effect.

Long-term epidemiological evidence supports the safety of a cup or two of coffee a day; more than that, however, can have adverse effects in some people.

Folic acid is also an important counter to depression
Folic acid deficiency has been linked to depression in clinical studies. This deficiency causes serotonin levels in the brain to decrease. Psychiatric patients with depression have much higher rates of folic-acid deficiency than the general public.

Depression can be relieved by as little as 200 micrograms, an amount easily obtained in a cup of cooked spinach or a glass of orange juice.

A lack of selenium can cause bad moods
Individuals suffering from too little selenium have been shown to be more anxious, irritable, hostile and depressed than people with normal levels of selenium. Selenium may have some unknown neural function, but as of yet, its mode of action is unknown.

Enough selenium to correct a deficiency will normalise mood, but more does not elevate mood further. Be sure to get your daily dose by eating a Brazil nut, tuna sandwich, sunflower seeds, wholegrain cereals or swordfish.

Put eggs back in your diet to improve memory and concentration
One nutrient that many of us tend to lack, in our fervour to avoid high-cholesterol foods, is choline. Choline is a B-complex vitamin that is concentrated in high-cholesterol foods like eggs and liver. A lack of choline can cause impairment of memory and concentration. Choline is a precursor to the brain neurotransmitter acetylcholine, which is linked to memory.

People given drugs that block acetylcholine fail memory tests, and low levels of acetylcholine have been linked to Alzheimer's disease and poor memory. What a good excuse to put eggs back on your diet plan!