The best way to start the day

Breakfast is meant to be brain fuel, but things turns out to be not quite that simple, says Richard Lovett

"EAT a good breakfast -- it's the most important meal of the day." If there is one dietary message that generations of mothers have drummed into their children, this is it. The advice to mothers has always been similarly clear: feed your kids the right stuff for breakfast and they will be able to concentrate all morning. Feed them poorly and they will struggle to stay awake in class.

Yet this tried and trusted advice has started to come unstuck. As we learn more about the way the body and brain regulate sugars, the idea that breakfast is always the best way to start the day is increasingly being challenged. In fact, eating breakfast can sometimes be worse for mental and physical performance than going hungry.

Of the many nutrients in your diet, the brain can use just one for fuel -- glucose --which your body derives from carbohydrates in food. Unfortunately, says Leigh Gibson, a biopsychologist at Roehampton University, London, this simple fact has led to several myths. One is what Gibson calls the "mythology of the sugar rush". The myth goes like this: after eating a high-carbohydrate meal or sugary snack, the level of sugar in the blood rises rapidly, sending a rush of glucose to the brain. This provides it with a temporary boost of power, but is swiftly followed by a sugar crash and a dip in mental energy.

In a recent article in the journal Nutrition Bulletin, published by the British Nutrition Foundation, Gibson reviewed 25 years' worth of research into the effects of glucose on the brain. He concluded that while the brain certainly does run on glucose, the idea that eating sugary foods will boost mental ability is at best an oversimplification.

The sugar-rush myth stems from what is known as the oral glucose tolerance test, which measures blood glucose levels in people who have fasted overnight and are then given a super-sweet glucose drink. This test, which is designed to help diagnose diabetes, does produce a rapid spike in blood glucose, often followed by an overcompensating crash.

In the real world, though, nobody eats pure glucose, and most people's bodies are pretty good at regulating blood glucose levels. Even when you consume a carbohydrate-loaded meal, it takes time for all the carbohydrates to be broken down into glucose, and a sharp spike in blood glucose after a meal is rare.

Unless you have type 1 diabetes, a rise in blood sugar levels prompts the pancreas to secrete insulin. The liver responds to the insulin by converting excess glucose into a starchy material called glycogen, which it stores for future use. When blood sugar levels fall again, the liver breaks down its stored glycogen into glucose, which it dribbles back into the bloodstream as needed. When functioning properly, this regulatory system controls blood glucose levels pretty tightly, so your intake of carbohydrate is not directly linked to what the liver is releasing back into the bloodstream.

There's also a second checkpoint between the carbohydrate in the food you eat and the glucose taken up by the brain. Research in the mid-1990s revealed the vital role of brain cells called astrocytes, which store glucose as glycogen and act as a buffer between glucose in the blood and that in the fluid that nourishes the brain. The astrocytes typically keep glucose levels in this fluid at just 20 to 30 per cent of blood levels. If the brain's neurons need more, they take it from the surrounding astrocytes. If they don't, the glycogen stays in storage. Only after a long period of demanding mental activity does the brain deplete the astrocytes, and then the blood glucose, to the point where it needs topping up with food.

Another myth is that because your brain subsists on glucose, it will perform better if you feed it glucose-producing carbohydrates before asking it to do anything important. Again, it's not actually that simple. Claude Messier, a neuroscientist at the University of Ottawa, Canada, gave rats a dose of the sugar-like compound 3-O-methylglucose, which can be thought of as a biologically useless form of glucose. At first glance, the brain cells mistake it for glucose, and happily scavenge it out of the bloodstream. But when they realise what it is, they spit it back out, like a vegetable-averse child rejecting a hidden pea. Metabolically, this should be a non-event: useless molecule in minus useless molecule out should equal no extra brainpower. Except that's not what happened to Messier's rats. Real glucose perked up their performance on memory tests, such as mazes, but they performed equally well on the metabolically inert 3-O-methylglucose.

"That's quite a conundrum," Messier says. "The only way I could figure it out is if the action of transporting the 3-O-methylglucose across the cell membrane triggered some signal in the brain that there was energy coming in. That got translated to promote memory." So much for the feed-the-brain theory. Fool-the-brain works too.

When it's not being tricked in experiments, though, your body has glucose regulation pretty much under control. So does it matter what you eat for breakfast? Well, yes, but not necessarily in the way your mother thought. Having reviewed nearly 100 studies Gibson is convinced that a small amount of carbohydrate can improve memory function on standardised laboratory tests, but it's a fairly tight response with the optimum dose the equivalent of about 25 grams of glucose -- or 100 calories of carbohydrate. A banana, in other words, or a small bowl of breakfast cereal. But recent experiments have shown that the type of carbohydrate is more important than the amount you eat. The crucial factor is the food's glycaemic index (GI), a measure of how quickly it raises blood sugar compared with pure glucose. Low-GI foods are digested slowly, releasing sugar into the blood gradually, while high-GI foods release their sugars in a single, large hit (see "Brain food", right).

Gibson fed breakfasts with varying GIs to volunteers, while others went hungry. He then gave each group lists of words to memorise and tested them on how many they could remember, both immediately after seeing the words and after a short delay. The experiments revealed that, contrary to the idea of the sugar rush, the best memory boosters are foods that have a low GI -- in this case, All-Bran. Surprisingly, the poorer brain fuels were those with a high GI, such as the Coco Pops (known as Cocoa Krispies in the US) used in Gibson's experiments, or cornflakes. "They both were better than no breakfast at all, but the performance was greater for the low-GI All-Bran than the high-GI Coco Pops," Gibson recalls (see Graphs, below).

It seems counter-intuitive: the brain needs glucose to perform, yet seems to prefer slow release over a short sharp hit. Gibson thinks the explanation for the test results lies in the hormone cortisol, which is produced in response to stress, as when anticipating an exam or, in this case, being examined by psychologists. Cortisol's natural function is to mobilise the body's resources for fight or flight. In small amounts it may enhance memory, but it doesn't take much to have the opposite effect. "If you have a lot of cortisol washing around, it tends to be correlated with impaired memory performance," Gibson says. "You need a bit, it seems, to perform well. But if you have too much, you perform badly."

Previous studies by Clemens Kirschbaum, now of the department of biological psychology at the Technical University of Dresden, Germany, have shown that consumption of carbohydrates, particularly high-GI carbohydrates, increases the production of cortisol in response to stress. So there may be a trade-off between carbohydrates as brain food and carbohydrates as magnifiers of the brain-draining stress response. That, Gibson suspects, is why a little bit of carbohydrate is good for mental acuity, but more isn't. "I think it's a beneficial process and an impairing process fighting each other," he says. If you're not stressed out it may not matter, but if you are, you need to be particularly cautious about what you eat.

The catch is that this only applies reliably to verbal memory tasks, which make use of the hippocampus -- a part of the brain involved in memory and thought to be adversely affected by cortisol. Things are a bit different if you're preparing for a table-tennis match or a computer-game tournament, where reflexes, not memory, make the difference. To test people's performance at this type of activity Gibson's team showed volunteers the names of colours and asked them to push matching coloured buttons. The words were in coloured type, sometimes matching the word ("green" in green type, for example), sometimes not ("red" in blue type). This time, people did best with no breakfast, a bit better with high-GI cornflakes, and reacted slowest on a "good" breakfast of low-GI muesli (see Graph, left). So if speedy reactions are your goal, a bit of starvation might be in order.

This may be because cortisol isn't the only hormone that has a hand in regulating glucose. Another is ghrelin, which is produced by the stomach when you're hungry and helps to keep you alert. Eating fat and protein has little or no effect on ghrelin levels, but carbohydrates suppress its production. "Imagine you are driving a car hungry, rather than on a full stomach after a huge dinner," says Tamas Horvath, a neurobiologist at Yale University School of Medicine. "Being hungry promotes your awareness of your environment. If you think about a cheetah -- how it picks the prey and pursues it -- it obviously does it when it's hungry. A hungry animal is much better at responding to visual and olfactory cues."
Brains for breakfast

Ghrelin also affects memory and learning. Horvath has found that rats and mice perform better in mazes and other memory tests if their ghrelin levels are artificially elevated. He has also found that ghrelin increases the levels of neurotransmitters associated with increasing the strength of neural connections, which is the way that brain cells come to respond more strongly with each repetition of a stimulus. "At the level of the cell, that's the basis of learning," Horvath says.

This means that having some ghrelin in your system is a good thing, even if you're not a cheetah chasing an antelope. In fact, it's probably another reason why Gibson found light meals to be optimal -- just enough to dull hunger and provide a bit of extra glucose without making you feel too lethargic. "It might be beneficial, when you go to that test or interview, to go with a reasonably empty stomach," says Horvath.

All this advice comes with a health warning, though. One thing all the lab studies have in common, Gibson says, is that the results can vary, not only from experiment to experiment but from person to person depending on their sensitivity to stress and, crucially, how well each individual regulates glucose. Poor glucose regulators are not necessarily diabetic, but their blood sugar fluctuates relatively strongly in response to what they eat. That means they react to low-GI carbohydrates the way other people react to higher-GI ones. It also means that their blood sugar can dip to unusually low levels overnight so, for these people, skipping breakfast could be a very bad idea. This can only really be measured in a lab, but there are signs to look out for, such as feeling unusually hungry, nervous, shaky, weak or light-headed after missing a meal.

In memory tests, Messier has found that poor glucose regulators tend to get a bigger benefit from breakfast than do people with good glucose regulation, probably because their blood sugar is more in need of a boost. He concludes that unless you're sure you are a good glucose regulator, it's not a great idea to fast before any kind of important mental activity. "Ideally, eat something that is a slow-release type of carbohydrate," he says -- "the 'good things' that digest slowly."

Gibson agrees. He says that good glucoregulators who are not too stressed out will probably do well on a bowl of porridge or muesli. For an afternoon test, a small serving of pasta salad for lunch should do the trick. Either way, think in terms of 25 grams --or 100 calories -- of slow-release low-GI carbohydrate, though you can also add some protein or fat if that's not enough to stave off hunger. If you are super-stressed out, this might be too much. If, however, you are a poor glucoregulator, it might not be enough. Ultimately, one piece of advice emerges that your mother probably could have guessed: if it's brainpower you're after, go for a small bowl of porridge, not a big bowl of sugar.
BRAIN FOOD

GI is a measure of how quickly blood sugar rises after eating a food, compared with pure glucose (GI = 100). A low-GI breakfast improves memory, while high-GI foods are better for quick reactions

LOW GI

Whole milk (27)
All-Bran (42)
Porridge made
with water (42)
Orange juice (46)
Banana (55)

Medium GI

Muesli (56)
Shredded Wheat (67)
Weetabix (69)
Wholemeal bread (69)

High GI

White bread (70)
Bagel (72)
Watermelon (72)
Cheerios (74)
Coco Pops/Cocoa
Krispies (77)
Cornflakes (84)

GRAPH: MEMORY PERFORMANCE For memory tasks like remembering words from along list, a low-GI breakfast is best

GRAPH: REACTION TIME For tasks requiring a quick reaction, such as identifying words flashed on a screen, no breakfast is best

GRAPH: SUGAR AND STRESS Levels of cortisol rise more sharply in response to stress in people who have been given glucose beforehand

PHOTO (COLOR): Eat the wrong kind of breakfast and you might find your brain lets you down

PHOTO (COLOR)

~~~~~~~~

By Richard Lovett

Share this with your friends