Is This Really the Delboeuf Illusion or Does Plate Size Truly Matter?
Lena Bauer
2026-03-19
3 min. read
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The persistent problems of epidemiology necessitate a constant search for their causes and solutions. The two opposing problems of the modern Western world - obesity and anorexia - require further knowledge and development of more effective treatments. It turns out that in both cases, seemingly insignificant environmental factors can have a significant impact on the way we eat and the amount of food we consume. To such seemingly insignificant factors belong m.a. color and size of dishes. How do these factors affect our brain? Can the right size of a plate be a crucial factor in treatment and prevention?
This is Delboeuf's illusion
To try to explain some of the mechanisms that govern our food choices, let's go back to 1865, when Delbouf made some observations. He showed that there was some visual illusion associated with seeing the dimensions of circles. Between two circles of the same dimensions, the one surrounded by a circle of larger diameter, seemed to be smaller than the circle surrounding it by a smaller diameter. Both of these dark circles actually have these same dimensions.
Is there an effective method to circumvent the Delboeuf optical illusion when assessing portion sizes?
Two fundamental factors shape our perception of portion sizes: the mechanism of contrast and the phenomenon of similarity. The contrast between the edges of the food portion itself and the boundaries of the plate significantly amplifies the effect of this well-documented visual illusion. One strategic approach to mitigating this effect involves the use of tableware lacking distinctly defined borders—such as plates without a dark rim that further accentuates their contours. Meanwhile, the similarity effect, which likewise diminishes the sharpness of vessel boundaries, operates on a comparable principle. For instance, opting for a tablecloth in a more subdued hue—white, for example—instead of a black one that starkly emphasizes the shape and dimensions of a white plate causes the dish’s edges to blur to some degree, thereby preserving an undistorted perception of portion size. Furthermore, mindful focus on the act of eating facilitates subconscious calibration of the amount of food consumed. It is no coincidence that experts emphasize the importance of dining in a conducive, tranquil environment free from distractions. While one might assume that food intake is solely governed by personal willpower, cognitive factors—such as the optical illusions discussed—must not be overlooked. To minimize the risk of misjudging portion sizes, it is advisable to serve food with full awareness and concentration, while also carefully selecting tableware. It is equally important to recognize that even a modest but consistent caloric surplus can, over time, contribute to gradual weight gain.
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