Why we crave sugary snacks... and not fruit and veg

By ALICE SMELLIE

Are urges to eat unhealthy food purely down to greed? We ask experts...

It is the question that has foxed dieters and scientists alike: Why do we crave sugary snacks or fat-laden junk foods and not more healthy options such as, say, an apple? 

Some claim to have 'a sweet tooth', or 'a salt tooth'. And many believe cravings are the body's way of telling them what they need. But how true is that really?

THE EVOLUTION OF CRAVING


Experts believe that cravings occur for a variety of reasons. They attribute them to evolution, psychological factors such as stress and unhappiness, and - sometimes - a genuine need for certain foods.


'It's crucial to remember that a food craving is not simply hunger,' says Professor Andrew Hill, Head of the Academic Unit of Psychiatry and Behavioural Sciences at Leeds University.


Hunger is the body's way of making sure it is provided with energy, in the form of nutrients from food. When the stomach is empty, it releases the hormone ghrelin, which communicates with the brain's command centre, the hypothalamus. This creates the feeling of hunger and is how we know when to eat.


Satiation is signalled by the release of the hormones leptin by fat cells, and insulin by the pancreas, in response to increased blood sugar.


Cravings, however, are much more complex.


'Those who are starving will eat literally anything - even foods they do not enjoy - to stay alive,' says psychologist Dr Leigh Gibson, Reader in Biopsychology at Roehampton University.

'Cravings, on the other hand, are an overwhelming sensation of desire for a certain food. There are a number of chemicals in the brain that are associated with this.


'First, there is dopamine, a brain chemical that is involved in learning and concentration. When we see or experience something new, dopamine is released in the brain.


'This works in tandem with other brain chemicals called opioids, which give us feelings of enjoyment and pleasure. The combination of these two factors mean that the brain associates certain activities with pleasure, and it teaches us to do them again and again.


'From an evolutionary point of view, junk food cravings are linked to prehistoric times when the brain's opioids and dopamine reacted to the benefit of high-calorie food as a survival mechanism.


'We are programmed to enjoy eating fatty and sugary substances, and our brains tell us to seek them out.


'Today, we still have the same chemical reactions to these so-called hyper-palatable foods, causing an unignorable desire - despite there being less of a nutritional need for them.'

HOW MOOD PLAYS A ROLE


Another factor in desire for sugary or fatty foods is stress.

'The body produces a hormone called cortisol in response to stress,' explains Dr Gibson.

'Its primary functions are to increase sugar in the blood to be used up as energy by the body's cells, suppress the immune system and aid in fat, protein and carbohydrate metabolism. It also blocks the release of leptin and insulin, increasing hunger.


'This is why studies have shown that when we're stressed, we're more likely drawn towards high-energy foods, such as cakes and sweets. Stress in response to danger used to mean energy was burned up. Stress down to today's lifestyle may have the same effect, though these days we are less likely to actually burn off the calories.'


Then there are the psychological components to cravings.


'Mood is unquestionably a potent context - especially negative mood,' says Prof Hill.


'We crave reward foods. The pattern for this is partially set in childhood when parents give us sweet food to show love or reward.'


Anna Raymond, of the British Dietetic Association, agrees.


'Cravings are a psychological need for high-fat and high-sugar foods which taste pleasant - but which should, of course, form only a small part of our daily intake.'


Dr Gibson points out that sweet food can actively alleviate pain by releasing opioids, thus excusing us for giving sweets to a hurt child. Researchers at the University of Michigan found that chocolate causes the brain to release these euphoria-inducing chemicals.


Unsurprisingly, more than 50 per cent of reported cravings are for chocolate and most others are for highly palatable foods such as sweets or biscuits.

'Chocolate melts at body temperature which gives a pleasant sensation, and fat and sugar further increase the sensory appeal,' says Prof Hill.


Gender can influence the nature of cravings. According to Prof Hill, studies show that women predominantly crave sweet, fatty and energy-dense food and men have more savoury cravings, although it is not yet understood why.

SOME CRAVINGS REALLY SHOULDN'T BE IGNORED


Sometimes cravings may point to a deficiency in the body. Dr Gibson conducted an experiment in 1995 to test this theory.


His team gave a group of volunteers a low-protein breakfast followed by a high-protein lunch. The following day they were given a low-protein breakfast and a low protein lunch. Each meal was given in a variety of flavours.


On the third day they were given a choice. Regardless of flavour, all participants chose the high-protein option. This proves that if we need a nutrient - such as protein - we'll automatically choose it.


'We know that animals seek out food when they have nutritional needs - such as iron, vitamins or sodium.


Why should we be any different?' says Dr Gibson. ' Cravings for healthy food are more likely to be down to bodily needs.'




WHAT YOUR CRAVINGS ARE TRYING TO TELL YOU...

CHOCOLATE AND SWEETS


'Cravings for these are usually down to a psychological desire for a food that makes you feel better and gives a short-term ''fix''. Dark chocolate contains magnesium, antioxidants and iron - so there is unquestionably some nutritional benefit,' says nutritionist Zoe Harcombe.

PIZZA, PASTA, CRISPS


'It may be an example of wheat intolerance in the case of pizza and pasta - ironically if we're intolerant of things we crave them,' suggests Harcombe.

'One theory is that if we don't digest or absorb foods properly, we desire them more as the body isn't getting what it needs from the food. For instance, diabetics can't regulate their blood sugar, leading to low energy levels. But if the condition is uncontrolled they crave sugary foods, as the body believes it isn't getting enough.' 

FISH

Should you crave salmon, it could be a need for Omega3 fats.

'Some new evidence suggests that taste receptors respond to certain fatty acids,' says Dr Gibson.


'Maybe our system is aware of their presence. Tuna could be a need for salt - especially in a low-fat dieter who eats lots of fruit and vegetables but little meat or fish and is getting little sodium,' says Harcombe.


'Dieters are eating more potassium by consuming large amounts of fruit and vegetables, so they need to balance it out with more sodium.'

DAIRY


'Milk contains key nutrients, and if you crave cheese, you may need the fatsoluble Vitamins A and D, especially if you have a lowfat diet,' says Harcombe.

MEAT


It seems obvious - but some experts believe a meat craving means the body needs protein. Dr Gibson says: 'A desire to eat red meat could be attributed to iron deficiency - especially in pregnant women.'