In 1865 Joseph Delboeuf, a Belgian philosopher and psychologist, described an interesting perceptual illusion with which most of you will be familiar. In the 2 diagrams above, the inner circles are the same size although the circle on the left looks larger. It is this optical illusion which appears to explain the findings of a recent study on plate size and food consumption.
The average dinner plate has increased in size by about 23% since 1900 and researchers wanted to know whether changes in tableware could be influencing food portion sizes. In one experiment 225 study subjects were asked to pour a specified amount of tomato soup into several different sized bowls. As expected, participants consistently poured less into the smaller bowls and significantly more into the larger bowls. In fact using large bowls led people to over-serve by up to 31%. The reason is that the larger bowl (or dinner plate) is equivalent to the test circle with the much larger circle around it, which in turn makes the food portion look smaller and so you tend to serve larger portions.
Interestingly, even telling subjects ahead of the experiment, failed to prevent the over-serving. It seems that the illusion is so deeply embedded in our brains it is almost impossible to override, even when we want to.
The scientists also looked at how colour influences portion sizes, specifically the colour of the plate and the tablecloth. If a white plate was placed on a black tablecloth, portion sizes tended to be 10% larger, whereas a white plate on a white tablecloth eliminated this bias. Again, the explanation is to do with the Delboeuf illusion referred to above.
So it seems clear that we are pre-programmed to over-serve on larger plates and under-serve on smaller ones and these differences are due to our perception of the relative gap between the edge of the food and the edge of dinnerware. Whilst the differences may be small, over time they could amount to a significant calorie gain. If the differences in bowl or plate size encouraged a person to consume just 50 calories more per day, this would result in a gain of around 5lbs a year.
So if you are trying to achieve or maintain a healthy weight, it might be a good idea to serve your food on small white plates and dump any coloured tablecloths!
Dr David Ashton MD PhD
26th June 2012