The Psychology of Dieting Part 5: Watching What You Eat

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Brian Wansink Bottomless Bowl

I’m sure you’ve heard the expression, “Watch what you eat.” The idea, generally, is to be mindful of what we’re eating–to be careful not to eat too much and to be more discerning about what we do eat. But, it turns out that literally watching what we eat–or watching food diminish on our plates–can have a psychological effect that prompts us to feel “full” and stop eating.

The Bottomless Bowl

In a 2005 experiment, Professor Brian Wansink and his team of researchers published a study called, “Bottomless Bowls: Why Visual Cues of Portion Size May Influence Intake” in the journal Obesity Research. In the study, the team of researchers sought to understand the influence of visual cues on the quantity of food consumption. In other words, could an emptier bowl serve as a sign to people that they have eaten more? Here’s what the researchers did…

For the control group, the researchers simply gave a bowl of soup to each participant and gave them 20 minutes to eat it while engaging in casual conversation with other other participants. When the time was up, each participant had to fill out a questionnaire estimating how much soup they believed they had eaten and judging how full they had felt from eating the soup.

For the experiment group, the situation was exactly the same–with one exception. The soup bowl was connected to a hose that ran underneath the table–refilling the bowl when it reached a certain threshold. As a result, the participants in the experiment group did not see the soup in their bowls diminish to the same extent as those in the control group.

So, what did the researchers find in this experiment? Here are a few takeaways:

  • Participants with the refilling soup bowls ate 73% more soup (14.7 vs 8.5 ounces) than those with the ordinary bowls.
  • Participants with the refilling soup bowls did not believe that had eaten any more soup than those with the ordinary bowls. In fact, while those with the ordinary bowls estimated eating 32.3 fewer calories than they actually ate, participants with the refilling bowls estimated eating 140.5 fewer calories than they actually ate.
  • Even though participants ate an average of 113 more calories from the refilling bowls, they were no more likely to say that they were full after eating their soup than those who had eaten from the ordinary bowls.

In other words, we don’t get full because we’re full; we get full because our plates are emptied and the signal is sent to our brains that we should be full. When there is no signal, we eat more and we just don’t get full.

Your Stomach Is Only As Big As Your Eyes

There are a couple other experiments worth noting that point in the same general direction.

In a 2007 article published in the journal Perceptual and Motor Skills, researchers tested another visual effect on appetite. For the control group, the researchers invited a group of graduate students to have an endless supply of wings. As the students finished the wings, the waitress would “bus” the tables. She would collect the plates full of bones and replace them with new plates.

For the experiment group, the researchers invited another group of graduate students for an all-you-eat wing party. Only, this time, the researchers instructed the waitresses not to bus the tables. While fresh plates were brought out for the students, the plates of bones were left on the table for the students to see. With the visual cue, the students were able to see clearly how much they had eaten during their meal.

When all the bones were counted at the end of the experiment, the participants who could see the plates of bones on their tables ate an average of 27% more (7 vs 5.5 wings) than those who could not. Just seeing how much they had eaten caused them to eat less than they otherwise would have.

In a 2010 article published in the journal Appetite, researchers tested the visual effect of food on appetite by playing with lighting in a restaurant. Participants were invited to a restaurant to eat a meal served in complete darkness. Unbeknownst to the diners, though, half of the group was given a super-sized portion of food.

At the end of the meal, the participants who had been given the larger amount of food at 36% food than those who had been given the normal portion. Moreover, when asked if they wanted to dessert, the group who had been given the super-size meal was no less likely to say “yes” than the group that had been given the normal-sized portion.

Again, we don’t stop eating when our stomach sends the signal to our eyes; we stop eating when our eyes sends the signal to our stomachs. So, if you’re trying to lose weight, you might want to pay a little more attention to your food as you’re eating it. Here are some tips…

  • Always portion your food. If you must eat potato chips, put them in a small bowl so you can see them diminish as you eat them. If you leave the entire bag on the table, you will eat until the bag is empty.
  • Leave visual cues for yourself. When you eat pizza, leave the crust. When you eat wings, leave the bones. If you eat candy, collect the wrappers. Leave a trail that shows you how much you’ve been eating.
  • Don’t eat in the dark. Out of sight, out of mind. Out of mind, into stomach. If you don’t see yourself eating it, according to your brain, it never happened.

The Curiosity Manifesto: Investigate

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