New research contradicts a common diet tip believed to help people eat less. The popular tip follows that serving food on a smaller plate tricks a person into believing they are eating more than when served the same amount on a larger plate. However, a new study published in Appetite suggests that when people are hungry, plate sizes don't matter – they are more likely to dish up the same amount of food regardless of how it's served.
The long-held belief takes after the Delboeuf illusion, an optical illusion on how people perceive size. In the experiment, two identical circles are placed near each other, one of which is surrounded by another circle. The surrounded circle seems larger than the other. When it comes to dieting, previous research suggests people perceive food proportions differently depending on whether it is served on a larger or smaller plate. If you’re looking to eat less, serving food on a smaller plate was thought to trick the eater’s mind into believing they are eating more, allowing them to consume less. However, other research has recently begun to call this belief into question.
"Plate size doesn't matter as much as we think it does," said Dr Tzvi Ganel in a statement. "Even if you're hungry and haven't eaten, or are trying to cut back on portions, a serving looks similar whether it fills a smaller plate or is surrounded by empty space on a larger one."
Researchers gave study participants photos of pizza placed on large and small trays to one group who hadn’t eaten for three hours and to another group of people who had eaten recently. Those who were hungry were better equipped to judge proportions, but that’s where the ability to accurately perceive size ends. Both groups were then asked to compare black circles and hubcaps placed in differently sized circles – a task they were equally bad at.
As it turns out, hunger stimulates a human response strong enough to resist being fooled by an optical illusion, reducing biases for food but not other stimuli.
People who aren’t hungry, though, are less likely to identify food proportions correctly.
"Over the last decade, restaurants and other food businesses have been using progressively smaller dishes to conform to the perceptual bias that it will reduce food consumption," said Ganel. "This study debunks that notion. When people are hungry, especially when dieting, they are less likely to be fooled by the plate size, more likely to realize they are eating less and more prone to overeating later."