The Delboeuf Illusion is an optical trick which causes us to misjudge the size of identical circles when they are surrounded by larger circles of varying size.
Discovered by Joseph Remi Leopold Delboeuf this illusion translated onto our dinner plates means the same portion of food looks smaller and less satisfying when served on a larger dish. Couple this with the fact our plates have grown by nearly 25% since the 1900's and you can see why we are subconsciously expanding our portion size with increasingly large piles of food.
With this knowledge in mind, down sizing your plates and keeping the larger ones for special occasions can be an effective way to effortlessly cut calories and lose weight.