Watching one’s weight is especially important during the holiday season. Lots of fad diets and dietary products promise miraculous results but ultimately prove to be mere illusions.

There is, however, one illusion that can help keep the pounds off. Learn about the Delboeuf illusion and how it can help you get past the holidays without unwanted extra pounds.

It was the Belgian philosopher, mathematician, experimental psychologist, hypnotist, and psychophysicist Joseph Remi Leopold Delboeuf (1831–1896) who created and described the illusion that bears his name. Consider the black circles in the image to the right. Which one appears to be larger? Most will answer that the circle on the right is larger than the one on the left. In reality, they are the same size.

Delboeuf was able to show that our perception of the size of an object is dependent upon the size of the object in which it is located.

This may have some curiosity value among brainteasers enthusiasts or in a geometry classroom, but the practical application of the principle can be found on the dinner table. In a 2012 study, researchers Koert Van Ittersum and Brian Wansink suggested that the Delboeuf illusion could be a factor in the choice of food serving sizes. The study tested three different bowl diameters and measured how individuals served themselves differently depending on the size of the dish. The results showed that people poured 9.9% more soup in larger bowls, and 8.2% less in smaller bowls, as compared to the control bowls.

The same study found that the color of the food, in contrast to the dish and the tablecloth could play a factor, as well. Food that is the same color as the dish does not create as much of a Delboeuf illusion effect. In other words, when dishing white pasta with Alfredo sauce on a red plate, a person is more likely to view a small helping on a small plate as being larger than the same size portion on a larger plate. If the meal is changed to colored pasta with marinara sauce, the food will blend in with the white plate, creating less of an illusion.