Many of us have heard that the size of our plate can affect how much we eat. Brian Wansink and his colleagues have done a tremendous amount of research on how visual cues affect consumption. For example, he has found that eating popcorn from a bigger tub, eating soup from a refilling bowl, and eating chicken wings where the bones disappear below the table all lead to more consumption.2,4,5 His general hypothesis is that much of the obesity in our society is caused by habits, with one very big habit being that we rely on visual cues to tell us how much to eat.1
Our Eyes Are Bigger Than Our Metabolisms
A recent study by Wansink and colleagues set out to see how visual cues (i.e., plate size) affect consumption.6 This study was actually made up of four separate studies that build upon each other. Study number one investigated how much people think is right to serve themselves. Cereal bowls were set out with differing amounts of cereal. Participants were asked two questions: how much is the appropriate serving and how much would you serve yourself. Interestingly, the responses for the two questions differed. Participants thought the most appropriate serving was when the bowl is about 66% full. However, they indicated that they would often serve themselves a bowl that was 75% full. Thus, it seems like there is already a conscious bias that people serve themselves more than what they think is an established norm. To say it another way, we fill our plates more than we know we should.
Plate Size Matters
Study number two investigated how much people serve themselves at a Chinese buffet-style restaurant if they use small or large plates. Participants in the study did not know they were being observed and could choose either a small or large plate to serve themselves. People who chose a large plate tended to put about 52% more food on their plate and ate about 45% more. One potential issue is that maybe these dinners chose the larger plate because they were hungrier and therefore they ate more. However, the results are consistent with other studies that show people tend to eat more when given a large plate. From a business standpoint, I can see why buffets tend to use small plates as it certainly cuts the cost of food preparation (or maybe they are thinking of the health of the consumers). The take-home point from this study is that we might want to purchase smaller plates for our homes.
Behavior Habits Are Hard to Break
The third study is quite intriguing as it involved human resource managers who were taking part in a three-day seminar on creating healthy organizations. The participants had just attended an hour-long lecture on how plate size can affect eating patterns. The point of the lecture was to pay attention to the amount of food on the plate and not on the proportion of the plate that is filled. After the seminar, participants were brought to lunch and randomly assigned to one of two buffet lines. The only difference in the lines was the plate size. As I was reading the study, I had that same feeling that I do when watching a horror film. “Don’t go in there.” “Don’t fall for it.” Even after just attending the lecture on food consumption and plate size, the larger the plate the more food that was consumed. That is, people still ate 50% more food even after hearing about how plate size affects food consumption. The habit of using a visual cue for eating seems like a tough one to break.
Our Estimations Are Illusions
Study number four investigated the cause of this relationship and how it affects our eating habits. Basically, we have trouble with the Delbeouf illusion. That is, we see different sizes depending what is the external reference. In the picture, the inner circle appears to be different sizes depending if there is a large circle or a small circle around it. We have this same difficulty with food. We have difficulties judging how much food there is as our brain tricks us into thinking there is more or less depending on the plate size. That finding is exactly what the researchers saw when people were asked to estimate soup portions. Our brain uses the external reference to guide us into how much there is of something. Most of the time this shortcut works. However, when it comes to estimating food the shortcut backfires on us.
How to Apply This Knowledge
There has been an ongoing philosophical discussion of whether the mind can override the instinctual aspects of our self. The argument has swayed back and forth between saying we are rational creatures and we are creatures of our emotions. From an evolutionary perspective, our instincts have had many more years to be refined and finely honed (an analogy would be the tenth version of software). The rational conscious system is relatively new (continuing the analogy, it is beta software). When it comes to eating it seems like we rely a lot more on habit than on our rational thinking side.
This fact is quite important when designing eating plans. We need to take the thinking portion out of it. We can’t rely on the will of the individual, as we need to change the cues that guide us what to eat. Probably the simplest solution is to find smaller plates. That is easy at home, but in restaurants it can be more difficult. One trick I use at Cheesecake Factory (home of some really large plates) is to keep the bread plate and move a fitting portion of my food to it. The remaining food on the serving plate I ask to be packed up to take home. I can overflow the bread plate and I feel very full afterwards.
Another idea is to keep tempting foods away. In another study by Wansink and colleagues, they found that moving a candy dish further away from people led to a lot less consumption.3 So, keep your healthy food choices nearby (and in small serving dishes) and the unhealthy ones inaccessible.
1. Wansink, B., Mindless Eating: Why We Eat More than We Think (Bantam:2007).
2. Wansink, B., and Junyong Kim. 2005. “Bad Popcorn in Big Buckets: Portion Size Can Influence Intake as Much as Taste.” Journal of Nutrition Education and Behavior 37 (5): 242–45.
3. Wansink, B., Painter, J. E., & Lee, Y.-K. (2006). “The office candy dish: proximity’s influence on estimated and actual consumption.” International Journal of Obesity, 30(5), 871–875.
4. Wansink, B., Painter, J. E. and North, J. 2005. “Bottomless Bowls: Why Visual Cues of Portion Size May Influence Intake.” Obesity 13 (1): 93–100. doi:10.1038/oby.2005.12.
5. Wansink, B., Payne, C. R., and Chandon, P. 2007. “Internal and External Cues of Meal Cessation: The French Paradox Redux?” Obesity 15 (12): 2920–24.
6. Wansink, B., and van Ittersum, K. 2013. “Portion Size Me: Plate-Size Induced Consumption Norms and Win-Win Solutions for Reducing Food Intake and Waste.” Journal of Experimental Psychology: Applied 19 (4): 320–32. doi:10.1037/a0035053.
Photo 3 courtesy of Shutterstock.