Karl Duncker: how to make children forget they love chocolate.

So much of what we think is personal taste is really the product of outside forces over which we have little control. The stories we hear  are sometimes just as powerful as the flavour of food in determining what we eat, and how we feel about it.

Karl Duncker was a remarkable scientist (1903-1940) whose food experiments speak to the way we eat now.  He is one of the heroes of the first chapter of my new book (First Bite: How We Learn to Eat). Duncker showed that we are - disturbingly - very easily influenced when it comes to our likes and dislikes. By making a group of nursery-age children listen to a story, he was able to convince them to forget - for a time - that they liked chocolate.  And this was in the 1930s when chocolate was a far more luxurious substance than it is today.

Duncker was a psychologist, a Gestalt theorist who fled Hitler's Germany in the 1930s and found work at the University of Cambridge.  He is now best known for his work on problem solving and the way we perceive different objects visually.  But in his short life, he also made some very important contributions to the psychology of eating. Duncker once wrote that his definition of the pleasure of anticipation was a child 'who has been told that he is soon to have a piece of candy ...glowing all over with happiness'.

Working with a nursery in Camden Town, London, Duncker devised a series of experiments to look at the role of social suggestion in forming food preferences. One of these was the white chocolate experiment. He took two substances. One was white chocolate powder flavoured with lemon - something practically guaranteed to taste delicious to young children. (As chocolate experts sometimes comment, white chocolate has the sweet blandness of babymilk). The other was valerian sugar, valerian being a very bitter and unpleasant herbal root used as a medicine.

Duncker then asked the nursery teacher to read the children a story about a hero, Mickey, a little field mouse, who hates one food - "hemlock", a poison - and loves another - "maple sugar". When Mickey discovers maple sugar in a tree he realises he has "never tasted such good stuff before". The hemlock in the story is "sour and disgusting". Apparently, the teacher read the story in quite a boring voice, yet the message was clearly heard.

After the story the children were invited to taste some real "hemlock" and "maple sugar". The "hemlock" was in fact - you've guessed - white chocolate. And the "maple sugar" was the mouth-puckering valerian. Yet when asked to choose the substance they preferred, 67 percent of the children opted for the "maple sugar" because of the positive associations. Only 13% chose it in a control group with no story. After the story, the majority rejected the "hemlock" even though many of them recognised that it tasted of chocolate.

Can our likes and dislikes be so easily influenced? Scarily, it would appear so. One simple story is enough to make children change their view of chocolate.  For Duncker himself, this was no surprise. Duncker had witnessed Hitler's rise to power. He knew just how "suggestible" human beings could be. To him, children being influenced in matters of food were in a similar situation to the population of Nazi Germany. At the time he was doing his peaceful chocolate experiments, Duncker's brother Wolfgang was living in exile in Moscow; he would eventually be arrested during the Great Purges of 1938 and died in the Gulag.   Duncker himself had been driven out of his academic post in Berlin because he had once been married to a Jewish woman.

'If educated adults can be made to discard their ingrained preferences because the leader has contrary ones, why should children [be different] even in such a vital domain as food?,' Duncker wrote.

Duncker's experiments were on a very small scale, but they should worry anyone who is interested in persuading children to eat a more balanced diet.  If a single story about a mouse hero could make children change their mind about chocolate to such an extent, what is the effect of the daily barrage of advertising we are all subjected to?  A child watching Saturday-morning TV is told many such stories. We are bombarded with images of godlike athletes drinking sweetened fizzy drinks. Why is it that the least nutritious, most sugary cereals are the ones with the cutest characters on the boxes?  In our own culture, it is not white chocolate that has "hemlock" status but green vegetables.  Many children grow up knowing that they are not expected to actually enjoy such foods as spinach.

The real question raised by Duncker and the white chocolate is what any of us can do in the face of the social pressure to eat in certain ways. How can we resist and find a way to eat the foods that do us good rather than the ones that are marketed at us?

Duncker offered himself up as an example of how individuals cam train themselves to enjoy new likes, through "inner reorganisation".   When he first arrived in Britain from Germany, he was disgusted to encounter something called "salad cream", a condiment beloved in the U.K. but nowhere else. It has the creamy texture of mayonnaise but a harsh tang from spirit vinegar. For Duncker, the taste of salad cream came as a nasty shock:

"When I first came to England, I was made to understand that raw green salad leaves could be made into 'salad' with the aid of a bottled substance of a yellowish colour, called salad dressing. It looked like mayonnaise; I expected mayonnaise - and I dare say I was deeply disappointed. No, I did not like it. But as I did not like raw laves either, I was therefore prompted to adopt the most favourable and adventurous attitude.  I tried it again, and I still remember the day when suddenly I discovered that this was not an unpleasant variant of mayonnaise but a kind of mustard which was no unpleasant at all. Thus by accentuating the mustard potentiality and suppressing the non-mayonnaise aspect, I came to like it".

There is huge wisdom here, about how we can change our preferences for the better, by adopting a more 'favourable and adventurous attitude'.  The change does not happen all at once, but through multiple exposures.   When the change comes, it is as if you are tasting a different food, one that reminds you of other familiar, homely foods that you love (for Duncker this was mustard). You might suddenly recognise that cabbage - once hated - has the same sweet crunchiness as broccoli.  Or maybe you wean yourself off sugar in your tea and one day find that the sugarless one actually tastes better.

We could read Duncker's experiment in a negative or a positive light. The negative aspect is that our tastes are learned in the face of colossal social pressure of one kind and another (from families to advertising). The flipside, however, is that because our tastes are so open to outside influences, we can learn new ones at any age, as the example of Duncker and the salad cream illustrates. Our tastes are not a life sentence.

Sadly, Duncker himself was struggling with problems that were harder to solve than his own food preferences. By the time he was working with the children in Camden Town, he had been suffering from poor mental health for years .  He yearned for his old life in Berlin but knew it was impossible for him to return while the Nazis were in power.  In 1938, he moved from Britain to the States to take up a new academic post at Swarthmore College.  Duncker committed suicide there, aged just thirty-seven, in 1940.