It's been known for some years that the size of your dinnerware impacts on how much you serve yourself (or others if you're playing host/hostess, or mom/dad). You pile less fodder into smaller plates or bowls, and vice versa. Makes sense, right? After all, your gluttony is curtailed by spatial limitations. But, it's not just a physical lack of space, or an abundance, that determines the disparity in how food is portioned out.
In 2005, Wansink, of Cornell University, and van Ittersum, of the Georgia Institute of Technology, showed that when consumers were asked to spoon a target amount of soup into bowls of various sizes they were just as apt to overfill large bowls as they were to underfill small bowls even when they were focused on pouring exactly the same amount into all the containers. The researchers knew then that there was something
going on in the human brain that makes us unconsciously misjudge serving amounts depending on the size of dinnerware. But at the time, they couldn't explain the phenomenon.
In the current study, party goers were given either a red or a white dinner plate and led to one of two buffet tables offering pasta; one in tomato sauce, the other in cream sauce.
Those given crockery which "matched" their food - red for tomato sauce, or white for cream sauce - gave themselves helpings between 17 and 22 per cent larger than those with plates of contrasting colour.
Researchers believe the phenomenon occurred because many people unthinkingly fill their plate, whatever size it is. A high contrast between colours may act as a "wake-up call" to examine the actual size of the portion.
Previous studies have already shown that buffet diners take bigger portions when given bigger plates, aided by an optical illusion which means a circle - or portion of food - appears bigger on a small plate than it does on a large one.
Further research has established that the average person eats around 92 per cent of a portion they serve themselves.
The latest study by researchers at Cornell University, in New York state, which was repeated several times on groups of 60 participants, found the actual colour of the food and plates made no difference; what mattered was the contrast between the two.
Research authors said the colour contrast appears to act as a "stop sign" reminding people to think about how much food they were serving.
Prof Brian Wansink, who runs Cornell University's Food and Brand Lab, which studies consumer behaviour, said: "People will generally serve themselves far more on a large dinner plate than they would on a smaller one, because the eye is tricked. It seems that colour contrast is one way to block this illusion."
The research author said those trying to lose weight could help themselves by buying brightly coloured or dark plates, to provide contrast with common white foodstuffs such as pasta, rice and potatoes.
Alternatively, green plates could be used as a way to trick children into eating more vegetables, he said.
Prof Wansink, president of the US Society for Nutrition Education and Behaviour said: "The secret of weight loss is a couple of small changes. One small difference like this every day could add up to a lot of pounds over a year."
Previous research by Prof Wansink has found that people eat 22 per cent less when they replace 12 inch dinner plates - now the average size used in the UK - with 10 inch plates, which were the most commonly used a decade ago.
Regardless of the size of their plate, people tend to fill around 70 to 80 per cent of it, he said, and to eat almost all of any portion they served themselves.
The lab's studies have also found that people pour far less into short wide glass than they do tall ones, and that children prefer meals with lots of different colours in them.
Chefs, restaurateurs, national fast food and quick service chains can incorporate the findings without compromising neither the taste and recipes of their offerings, nor their bottom line. "People are so distracted by talking, eating, and the noise and movement around them in restaurants that they are not going to notice a change in their plate size.
They're certainly not going to measure the china," says Karen Ansel, a spokesperson for the Academy of Nutrition and Dietetics. Because of the effect of the Delboeuf illusion, the change in portion sizes would be barely perceptible to diners. Indeed, the restaurant industry could follow the example set by food manufacturers who are reducing the sodium content of their products. "Chefs can
take the lead. They don't need to announce it, they can just quietly reduce the size of their dinnerware, or change the tablecloths in the same way that food companies are reducing salt without alerting consumers. Sure there's a cost involved in procuring new china or linens, but there's an even bigger cost involved with obesity"