Small Plate, Small Appetite? Researchers Debunk Popular Diet Theory

That trendy weight-loss theory that says tricking your brain into eating less by using smaller plates will help you lose weight? That’s likely a myth, according to Israeli researchers from Ben-Gurion University of the Negev.

A study published in the medical journal Appetite by Dr. Tzvi Ganel of the Laboratory for Visual Perception and Action in BGU’s Department of Psychology and BGU PhD student Noa Zitron-Emanuel found that when people are hungry, or food-deprived, they’re more likely to identify a portion size accurately, no matter how it is served.

The findings, say the researchers, debunk the use of the Delboeuf illusion, which predicts people will identify sizes differently when they are placed within a larger or smaller object, as a diet trick. Developed by Belgian psychologist Joseph Remi Leopold Delboeuf in 1865, experts say that the original illusion shows how our brains become confused by the size of objects depending on their circumstances.

Ganel, who says he only used food as part of this study as “meaningful stimuli” to visual perception – a topic he has been researching for years – claims that the perception of food is a different domain that can serve as significant neural representation in comparison to non-food objects.

“There is growing research on how people perceive foods and I think there is a reason for that,” Ganel tells NoCamels.

The Delboeuf Illusion. Photo via Wikipedia, CC By 3.0

The Delboeuf illusion, when applied to weight loss, only gained popularity in recent years, after a 2012 study where scientists asked their participants to serve themselves soup in bowls of different sizes. The people who used larger bowls poured themselves more soup than those with smaller bowls — which the researchers attributed to the Delboeuf illusion.

The idea was further explained in 2014 with a study from the International Journal of Obesity which found that participants overestimated the diameter of food on their plate when the plate had a wider rim in comparison to a plate with a thinner rim.

A study published in 2012 in the Journal of Consumer Research says that the association of plate size to the Delboeuf illusion has caused bias in restaurants and that they are now prone to serve meals on smaller plates in order to take advantage of the illusion.

SEE ALSO: Mediterranean Diet Can Bust Fat, Reverse Artery Damage

Ganel has a different viewpoint, however, after his study with Zitron-Emanuel, and it has to do with the use of hunger as a key variable.

Their study questioned the relationship between weight loss and this visual illusion as well as how the illusion affects basic perceptual abilities when hunger is involved, though they may not be affected in other instances.

In order to examine the different conditions, the team tested participants who had not eaten an hour before the experiment and those who had not eaten at least three hours prior. They presented the participants with slices of pizza on different size trays and asked them to compare the proportions. They found that the group that was deprived of food for longer guessed more accurately than the individuals who were less hungry.

An illustrative photo of pizza. Photo via Fancycrave, Unsplash

“Plate size doesn’t matter as we think it does,” Ganel said in a university 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.”

This only worked when applied to food, the research shows. Both groups were inaccurate in similar ways when asked to compare the size of black circles and hubcaps placed within the different circle sizes.

The researchers claimed this indicates that hunger stimulates stronger analytic processing that is not as easily fooled by the illusion.

The results showed that food deprivation reduces the “illusory bias” for food-related but not neutral stimuli. Reducing the effect of the illusion indicates “reliance on analytic, rather than relative processing style, for domain-specific stimuli when in the state of hunger.”

“We have a study in which we showed that when we are hungry, we are more precise in knowing exactly when the food portion changes,” Ganel says. The effect of the Delboeuf illusion “is misleading. It’s [an] inaccurate perception. It makes sense that we won’t be inaccurate when we need the food. The plate is not the part that we are interested in. It’s the food.”

The research and psychology of dieting, he explains, only came many years after scientists studied visual perception. There is a relationship between perception and what you eat, he says, but when we are deprived enough, we are less affected by the size of the plate.

Ganel says the pair will use its findings to help patients suffering from food-related disorders, like anorexia nervosa, which Zitron-Emanuel is already working on. While he wouldn’t disclose details, he did say that the pair currently has an international collaboration with patients who suffer from these types of disorders.

SEE ALSO: Could Personalized Diets Help Prevent Diabetes And Heart Disease?

“One of the things we are planning to do is to take this knowledge to patients and once we establish baselines for normal perceptions of food we will test it against other populations to see how they perceive food,” he explains.