Junk food is as addictive as heroin, it was reported recently.
It seems fatty and sugary snacks trigger the same pleasure centres in the brain as drugs - which could explain why many people just can't stop themselves bingeing on the stuff. It could also lie behind the obesity epidemic.
But it's not just unhealthy food that has a significant effect on health and behaviour.
Omega-3 oils (found mainly in oily fish, but also in walnuts, pumpkin and flax seeds) are good 'brain food'
Your brain weighs just 3lbs or so - a fraction of overall body weight - but it gobbles up about 20 per cent of your daily calorie intake. A brain-healthy diet is essential for keeping your memory and intellect sharp and your mood buoyant.
Here, we look at the latest thinking on nutrition and the brain - and the foods that help as well as those that hinder...
Good powers of concentration depend on keeping the messages flowing freely between brain cells.
These cells need oxygen to fire up and send a message, and they get it from blood sugar.
Simply ensuring an adequate and steady calorie intake throughout the day is therefore the first step to keeping focused and alert. It is not enough, however, for the signals to be generated - they also have to be sent from one cell to another.
This is done by nerve fibres. Just like electric wires, these fibres have to be insulated so the messages flow. In order to build these sheaths, the brain needs a fatty substance called myelin.
Omega-3 oils (found mainly in oily fish, but also in walnuts, pumpkin and flax seeds) help build and maintain myelin. This may be why fish oil supplements seem to boost children's mental performance, although studies showing this are controversial.
TOP TIP: Eating regularly - three meals a day - helps you to concentrate. Snack on walnuts and seeds.
LIFT YOUR MOOD
Our feelings, like all mental activities, involve a frenetic exchange of electrical messages between the brain cells.
The information is carried between the cells by chemicals called neurotransmitters - and these play a key role in your mood.
One of the key neurotransmitters is dopamine, the ' feel - good' messenger. Rising levels of dopamine give you enthusiasm, drive and pleasure. Falling levels are liked to a sense of emptiness, sadness, irritation and boredom.
Sugary and fatty foods cause a surge of dopamine. However, a quick dopamine high is invariably followed by an equally sharp drop, so to keep buoyant all day you are better off eating slow release, protein-rich foods.
Another way of ensuring a steady production of dopamine - and a continued good mood - is to supply your brain with precursors. These are the molecules which it uses to manufacture dopamine.
One important precursor called phenylalanine is found in beets, soybeans (available as edamame beans), almonds, eggs, meat and grains.
But if you really need a quick mood-boost, chocolate is especially effective at pumping up dopamine. That's because it contains anandamide - a fat molecule that resembles the active substance found in marijuana.
Another neurotransmitter, called serotonin, helps you feel serene and content, combating anxiety. A carbohydrate snack will raise your serotonin level quickly, but it will also make you sleepy, so again, it is better to keep the level steady.
To manufacture serotonin the brain needs tryptophan, a substance found mainly in eggs and meat - the good news is that a bacon and egg breakfast will supply your body with serotonin building blocks to last the day.
Alcohol also creates a sense of well-being in small doses - it does this partly by boosting dopamine.
In large doses, however, it leads to a hangover, which is characterised by low mood. And long-term overuse actually destroys brain cells, especially those concerned with memory.
TOP TIP: Try bacon and eggs for breakfast for a good mood throughout the day. Almonds and edamame beans are also good.
Caffeinated coffee is a classic remedy for sleepiness, but there's an art to using it properly.
Its effect is down to the way it binds to certain cell receptors in the brain.
These would normally soak up a substance that turns off electrical activity, making you drowsy. Caffeine effectively blocks this substance, so encouraging your brain cells to be more active, giving you a burst of energy.
Too much caffeine, however, produces nerviness because the pituitary gland at the base of the brain interprets this spurt of activity as warning of an emergency.
It then instructs the body to produce the 'fight or flight' hormone adrenalin. So while you'll become more alert initially, and your brain may work better and faster, you may also feel anxious - cancelling out your ability to think clearly. Stick to a single espresso.
Carbohydrates can also provide a energy hit because they create a surge of glucose.
But this in turn causes the body to release the hormone insulin - which makes you feel drowsy.
TOP TIP: A single espresso will boost your alertness, but a double will just make you anxious and muddle your thinking.
Our ability to remember things depends on getting brain cells to make new connections.
They do this best when they are highly excited - that is why we tend to remember events which happen when we are feeling emotionally or intellectually stimulated.
There is one key messenger in the brain which keeps brain cells excited - acetylcholine.
Vegetables such as cabbage, broccoli and cauliflower also seem to help memory
In fact, drugs which mimic the effect of this chemical have been found to boost memory in people with Alzheimer's.
This key chemical is made from choline, which is found in eggs, liver and soybeans.
Vegetables such as cabbage, broccoli and cauliflower also seem to help memory. Researchers found people who eat these do better than peers on memory tests.
TOP TIP: Eggs could make a real difference to your memory. Eat them regularly.
When you are anxious, your body produces stress hormones called glucocorticoids. These trigger the brain to seek ways to relieve the misery. And that's where sugary, fatty foods come in.
Studies of rats with high levels of stress hormones found they developed compulsive behaviours, including guzzling sugary drinks and eating lard.
The short-term effect was to lower their stress hormones and help them relax. However, the effect of comfort eating was to make them fat.
Over a long period, repeated exposure to sugar alters the way the brain responds - the body need more to get pleasure, so people get addicted in the same way they get addicted to drugs.
It's boring but true: the only way to prevent cravings is to avoid the substances that create them. If you are ambushed by a craving, you can either feed it or resist. Or try other dopamine-boosting activities, such as reading.
TOP TIP: Try to limit your habit. Or try other sorts of dopamine-boosting activities such as exercise or socialising.