Nudges by Chopstick

Brian Wansink and Collin Payne recently examined the relationship between Body Mass Index (BMI) and eating behaviors at all-you-can-eat Chinese buffets. The researchers found that customers with a higher BMI were more likely to use larger plates and to face the ever-tempting buffet. They were also less likely to use chopsticks (as opposed to a fork) or have a napkin on their lap. Wansink and Payne concluded that, “small changes in one’s environment may lessen one’s tendency to overeat.” (HT: Dmitri Leybman) [%comments]


Chopsticks slow you down. Forks are good but soup spoons are better for optimizing your calories per second.

Eric M. Jones

“small changes in one's environment may lessen one's tendency to overeat.” Hah! This is a clear confusion of cause and effect.

Sure, there is a high correlation with one's desire and tendency to stuff one's face and certain behaviours prevailing. But you can't draw the conclusion that changing one's behaviour will reverse the effect. The more likely effect is that the high-BMI individual will eat someplace else.

There is polite classy elegant dining...and then there is eating like a pig and shoveling it in.

I intend no offence to high-BMI individuals or pigs.

Howard Tayler

Correlation != Causality

It's time to hand the chopsticks and napkins to some fat folks and see if their BMI changes.


Couldn't the conclusion go the other way? That a persons overall eating tendencies (and resulting BMI) are what shaped their decisions on what size plate, utensil and seating position and that if those variables were changed the overall intake would be the same.

The conclusion would then be that they need to change their eating tendencies and that will lead them to follow the lower BMI choices (small plate, chopstick, back to buffet) and not vice versa.

The environments will always exist so the change needs to occur at a personal level for those environmental changes to actually work. I am guessing if provided with smaller plates high BMI'ers would just go up more.

An interesting follow up would be to take the high BMI group and have them utilize the low BMI eating behaviors and observe if there are any changes. That would prove or disprove my guess.


Seems there conclusion might be more correlation than causation. Those who overeat use forks because it's easier to stuff their faces and don't use napkins because they are too busy with their food. Forcing one to switch from fork to chopsticks would likely only slow them down and not actually decrease overall food intake.


Napkins on your lap are useless if your belly is large enough to catch any dropped food - sadly I speak from experience!


I suspect that higher incomes/ educations correlate with lower BMI, napkins on laps, not cleaning plates, and chopstick-using. And that's what they could be seeing here.


This could be simply correlation, but there is also some merit to hypothesizing that small changes may lead to reduced consumption. I use smaller plates at home because I know I'll eat whatever I put on it, and I'm going to fill it up regardless of size, so why not use the one that's got half the area? Same for ice cream - it goes in a small teacup or occasionally an espresso cup.

The effect in a buffet of having everyone use smaller plates and chopsticks is that it would force people to eat more slowly, by giving them a tool that is less efficient for shoveling and punctuating their servings with more frequent trips to the buffet. Thus they may start to feel full after having eaten less, simply because it takes a while to feel full and these tricks make you slow down so you've eaten less once the "full" feeling hits you.

If buffets switched everyone to small plates, sure - more people would take more trips to the buffet. But I bet there would be an overall small decrease in food consumption because most people wouldn't make enough extra trips to compensate for the lost capacity of the larger plates. It would also probably help the restaurant cut down on wasted food.



Oh, hooray, another study mistaking causation and correlation.

Travis L

Man I love the Freakonomics readers! I read the article, think "that sounds just like correlation to me..." Then I read the comments and the majority of them mention that as well!

Nice job fellow Freakos.


Agree with JES here, a lot of people are missing the point here.


Well how's this for the causation-correlation nay-sayers:
Give a random sample of buffet eaters small or large plates, and a fork or chopsticks. Track calories consumed as a function of eating surface/utensils and BMI.

Personally, I have a low BMI and I'm a complete pig. I'll routinely make several trips (3) to and from the buffet. I use as large a plate as I can and I use chopsticks (I can shovel pretty effectively after years of practice). I'm active with a high metabolism.


I think there actually may be some causation to this, and not just correlation.

I know it is much more difficult to eat with chopsticks, so that you may tend to eat less. It also takes more concentration, and I believe many studies have shown that people eat more when they are not concentrating on eating (such as while watching TV, or talking with others. If you are forced to concentrate on eating via using chopsticks, it seems plausible that you may tend to eat less.


Why do we assume the high-BMI individuals overeat? They could be eating normally (that is, to maintain their weight). Larger people need to eat more.

Of course it's another matter entirely whether they should be eating less, so that they lose weight, but presumably not everyone wants to do that.


Forget all the causation-correlation nonsense, this is just common sense: fat people eat more food faster than skinny people. Really? We needed a study to prove that?


I also agree with JES. If you doubt the causality, pick up a copy of "Mindless Eating." They do several carefully controlled experiments to determine which environment factors influence our eating behaviors.

Mike M

Once again, the poor metric known as BMI rears its ugly head.

Someone that has a high BMI may not be fat, and thus overeating isn't a problem.

For example, I know many strength athletes and body builder types that eat as much as possible to help pack on additional muscle mass. Of course these folks will eat more, that is the intention of going to those places in the first place!

Perhaps this is an over-reaction on my part, but I just loathe that metric. It doesn't tell us anything more than a ratio of height to weight, which is useless in describing the body composition of an athlete. I find it laughable that I am considered "obese" because my BMI is just over 30. In high school with well under 10% body fat i was well into the "overweight" classification.


Is that really small changes, or just correlation with social economic status and race?

From my personal observation, people who live in the big cities like NYC are more likely to know how to use chopsticks. They are more likely to have large variety of food choices in their diet.

For the napkin part, people in higher social economic status are more likely to have good dinning manners. And rich people make are healthier and thinner. Or do thinner people make more money?

Would using chopsticks help? There ARE obese people in Asia too, you know.


It seems that it would be in the interest of buffet-style restaurants to use this information to limit the amount consumed per customer.
They could move the buffet out of sight from the dining area, only stock small plates, make chopsticks more readily available and make forks smaller than average.

Of course most buffet restaurants currently limit the cost per customer by stocking the starting area of the buffet with the cheapest high carbohydrate food they have so people load up on that and eat less of the more expensive food at the end of the buffet.


I can't believe you are making this correlation/causality mistake.