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Prof. Koert van Ittersum: ‘If you want to stay slim, use a smaller plate’

23 December 2013

Anyone afraid of packing on the pounds during the forthcoming festive season can take a few simple precautions. Small plates and tall, narrow glasses will help you to eat and drink smaller portions, says Koert van Ittersum, Professor of Marketing and Consumer Well-Being at the University of Groningen. ‘This may seem logical because it means that you can fit less food onto your plate, but it’s not as simple as that. An optical illusion is actually the reason that people serve themselves larger portions on a larger plate and pour more drink into a wider glass. Even trained bartenders sometimes fall into this trap.’

Koert van Ittersum
Koert van Ittersum

Van Ittersum is studying the factors behind overconsumption of food, soft drinks, alcohol and medicines. He has already proved that the size of the crockery affects the amount people eat. For example, using a smaller plate seems to curb people’s tendency to serve themselves larger portions. ‘We demonstrated this using ice-cream. People with a double-sized bowl serve themselves a third more ice-cream. If they are also given a double-sized serving spoon, they help themselves to sixty percent more than the people using a small bowl and a small spoon. The strange thing is that they are totally unaware of the mountain of ice-cream in their bowls,’ says Van Ittersum emphatically.

Optical illusion

‘This is because people gauge the size of an object by comparing it with the size of the surrounding objects’, Van Ittersum continues. ‘People estimate the size of two identical circles differently if one of the two is inside another circle, for instance.’ This phenomenon has been known as the Delboeuf illusion ever since it was discovered by the Belgian philosopher and mathematician of that name at the end of the 19th century.

Colour and contrast

The Delboeuf illusion not the only illusion that affects calorie intake. Van Ittersum: ‘Colour and contrast also influence the amount of food people serve themselves. They pile more pasta onto a white plate if it is in a white sauce than if it is in a red sauce. The reason for this is also linked to the Delboeuf illusion. The white sauce does not contrast with the edge of the plate and so people keep trying to fill it. Placing a white plate on a white tablecloth, however, tones down the effect of the optical illusion.’

The effect of the illusion is difficult to dispel, says Van Ittersum. ‘If you tell people that they have served themselves larger helpings because they were given a large plate, bowl and spoons, they serve themselves smaller portions for a short while, but soon return to their old habits.’

Quiet surroundings

So Van Ittersum’s advice to people who want to stop eating too much is to change their crockery. It will not keep you fit and trim, but it will certainly limit the amount of food on your plate. ‘And think about the colour of your plate and tablecloth, the size of your serving spoons and the shape of your glasses. You tend to pour less into taller, narrower glasses.’

Quiet surroundings also help you to eat less. ‘We compared the amount people ate in busy and in quiet surroundings. People eating in quiet surroundings eat considerably less, despite taking longer over a meal. They also appreciate what they are eating more.’


Van Ittersum has identified a link between the growing size of crockery and obesity. ‘Large plates may look good, but they influence the way we eat. It is important to make people aware of this phenomenon. An extra fifty to a hundred calories per day on your plate will take their toll in the long run. It is particularly important that children are given small plates.’

According to Van Ittersum, the link between eating patterns and the size of crockery shows how subconscious processes affect the amount we eat. ‘We consumers are our own worst enemy in this respect; our subconscious mind has a massive impact. There’s very little we can do about it; we have to make so many decisions about our daily food intake that it would be impossible to be aware every single time.’


The food industry is only too happy to take advantage of this tendency, says Van Ittersum. ‘But this doesn’t make them the only culprits. People have a responsibility to themselves. It’s rubbish to say: “I weigh three hundred kilos and McDonalds is to blame.” The matter of where to draw the line between personal responsibility and the responsibility of the industry is an interesting issue. And of course, there’s the question of whether consumers want to be protected, and to what extent. People don’t like being patronized.’

Prof. Koert van Ittersum is Professor of Marketing and Consumer Well-Being at the University of Groningen.

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Last modified:15 September 2017 3.10 p.m.
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