Above: Image © Zoe Polando, iStockPhoto.com
Lots of toppings to choose from at this fro-yo shop. Image © andresr, iStockPhoto.com

Have you ever been to a frozen yogurt store? If not, sit back and try to imagine the following situation. It is a hot summer day, so you and your friends decide to cool off with some ‘fro-yo’. You walk in and pick up a bowl. Next, you head over to the frozen yogurt and test a few (or all) of the different flavours. You decide on salted caramel and butter pecan. As you pull the lever, you watch the frozen dessert swirl into your bowl.

Next, you go to the topping station. You sprinkle fresh strawberries, pieces of cookies and hot fudge sauce over your creation.

You’re just about ready to dig in! All that’s left to do is pay. How much does this delicious treat cost? It depends. The cashier will weigh your bowl. The more frozen yogurt and toppings you’ve served yourself, the more your bowl will weigh, and the more your dessert will cost.

If you have been to one of these stores, did you notice that many of them only offer one size of bowl? And in my opinion, that bowl is pretty large! It turns out that the size of your bowl can affect how much you eat - and how much you think you can eat.

Experiments in bowl size

Imagine you were given a large bowl. Do you think you would serve yourself more, less, or the same amount of frozen yogurt than if you were given a smaller bowl?

Scientists were interested in this exact question. To answer it, they did many separate experiments using different-sized plates and bowls. They also used all sorts of foods, from ice cream to cereal to stale popcorn. The result was the same in many of the experiments: People who were given a larger plate or bowl tended to serve themselves more food, and eat more food, than people who were given a smaller dish.

Here’s the strange part: This was true even when the participants said they didn’t like the food! For example, in one study, the researchers went to a movie theatre and gave groups of moviegoers either stale or fresh popcorn in a large or medium bag. After the film was finished, the researchers weighed how much popcorn each person ate and gave each person a questionnaire. The questionnaire asked participants if they agreed with the following statements:

  1. “The popcorn tasted good!”
  2. “The popcorn was of high quality.”

Not surprisingly, the people with the stale popcorn agreed with these statements less than the people with the fresh popcorn did. But the more interesting finding? Those with the large bag of stale popcorn still ate more popcorn than the people who had the medium bag!

Is the plate half full?

Scientists guess there are many reasons why people serve themselves more food on a bigger plate. One reason might be that your brain is fooled by something called a size-contrast illusion. If you fill a small plate with pasta, the plate looks full. But if you put the same amount of pasta on a big plate, the plate only looks half full. You might be tricked into thinking that this half-full big plate has less food than the full small plate. So when you use a big plate, you serve yourself more food.

Did you know? One study looked at the size of different dinner plates people were selling on the online shopping site eBay. This study found that the size of plates manufactured in the U.S. during the past 100 years has increased by 22%.

Portion sizes

Let’s think back to the frozen yogurt scenario from the beginning. You might get to the cashier and your ice cream costs a lot more than you thought. Why? Like I said before, many of these frozen yogurt stores only offer one size of bowl. These bowls might even be bigger than the bowls you have at home. Larger bowls mean you will probably serve yourself more frozen yogurt. And remember, the cashiers charge you by weight. So when the cashier weighs your frozen yogurt, you might be surprised by how much it costs.

When it comes to nutrition and healthy eating, it is important to think about not just what you eat (salad versus candy), but also how much you eat (a lot of candy versus a couple of pieces). Nutrition experts call the amount of food you eat in one sitting the portion size.

Portion size is especially important when the foods are high in sugar and/or fat. In North America, portion sizes keep increasing. It’s one of the reasons why North America is facing a problem with obesity.

Did you know? The sizes of food and drinks at many fast food restaurants in the United States are now double or more their original size.

But studies like the ones you just read about can help. Because of these studies, we now know that one way to eat less food is to choose a smaller plate or bowl. Bon appétit!

Learn More

Portion size: review and framework for interventions (2009)
I. Steenhuis & W. Vermeer, International Journal of Behavioural Nutrition and Physical Activity 6

Portion size
Medline Plus, U.S. National Library of Medicine

The Large Plate Mistake
Food & Brand Lab, Cornell University

Kaitlyn Bailey

Hailing from a small town East of Toronto called Port Perry, I moved away from home and studied Kinesiology at Queen’s University. My passion for research was sparked during a fourth year thesis project. I went on to conduct a Master’s of Science at the University of British Columbia (where in addition to top-notch research facilities I was exposed to great hiking and skiing too). My thesis investigated strategies and techniques to help people with diabetes increase their exercise levels. I stayed on at the University of British Columbia to teach two courses following my degree and I am currently aspiring to be a scientific journalist.