Does using smaller plates really help you eat less?

One of the most interesting books I’ve read in the last two years was Mindless Eating: Why  We Eat More Than We Think, by Brian Wansink.  It’s a fascinating exploration of the psychology of modern eating behavior and food marketing.  From the synopsis, here are a few of the questions it explores:

• Does food with a brand name really taste better?

• Do you hate brussels sprouts because your mother did?

• Does the size of your plate determine how hungry you feel?

• How much would you eat if your soup bowl secretly refilled itself?

• What does your favorite comfort food really say about you?

• Why do you overeat so much at healthy restaurants?

The third item on that list is the most widely known and discussed: numerous studies have found that people eat more when their food is served on larger plates.

In particular, the book cites research that the author himself conducted at the Cornell University Food & Brand Lab, in which subjects were invited to eat self-served cereal, ice cream or pasta.  In these studies, subjects consistently ate significantly more food when using larger plates or bowls vs smaller ones.

Notably, in at least one study the subjects were participants in a health and fitness camp who were presumably trying to practice healthy eating behaviors.  That means the phenomenon in question still occurs when people are making at least a modest attempt at eating mindfully. 

In a later study, Wansink and his research partner, Koert Van Ittersum, suggested that the average adult could lose 18 pounds in one year by eating off of 10-inch plates rather than 12-inch plates* for a whole year.2

Now, obviously they’re not accounting for the fact that fat loss will generally slow down if you eat the same diet indefinitely, but we’ll ignore the weight loss math.  The main problem with that recommendation is that it assumes every meal people eat will take place under conditions resembling those of the experiments. 

Here’s what the studies found: When adults were eating cereal, pasta or ice cream, which they served themselves, without being specifically told to eat less or track how much they ate, they ate more when using bigger bowls and plates. 

Here’s what most commentators say the studies found: When people eat out of smaller plates and bowls, they eat less, period.

The study results have thus been translated into diet advice that goes well beyond what the original studies actually supported.  Note the four big distinctions: that the subjects were adults, what the subjects were eating, the fact that they weren’t instructed to try and control their eating, and the fact that they served themselves.  Further research has made it clear that those three variables play a crucial role in the effect of plate size. 

Consider this a cautionary tale about how easy it is to misinterpret or excessively generalize overly specific research findings.

Note: I was just finishing the rough draft of this article when I saw the news that Brian Wansink may very well be a fraud.  His published work contains a tremendous number of errors, he routinely engages in self-plagiarism (not nearly as serious as plagiarizing other people, but frowned upon), and there’s compelling evidence of data manipulation in some of his studies.  Now, at least some of his findings have been replicated, though agreement bias have have played a big role in that.  I still consider his book worth reading, albeit with skepticism, as it doesn’t rely entirely on his own research.  Regardless, as you’ll see, there are plenty of other reasons not to jump on the small plates bandwagon.

What the research really says about plate size: It depends

A 2013 study published by the American Academy of Pediatrics confirms that plate size can have an effect on energy intake, but the effects are far, far more complicated than just “use smaller plates and you’ll eat less.”

In this study, children ate a self-served buffet meal consisting of an entree (either pasta or chicken nuggets), a vegetable side, and a fruit side.  They used either child- or adult-sized plates, with the adult-sized plates being twice as big is the child-sized plates.  The study used a within-subjects design in which all subjects tried each combination of plate size and entree twice.  The researchers measured how much the children served themselves, how much they ate, and asked them how much they enjoyed each food.

The researchers found that plate size had a significant positive impact on how much pasta, chicken nuggets and fruit children ate, as well as on total caloric intake, but not on vegetable intake.  Interestingly, plate size had twice as large of an effect with the pasta than with the chicken nuggets- it’s easier to fall for plate size illusions when the food isn’t measured into discreet units.  The effect on fruit intake was lower than on entree intake, though not much lower as a proportion of total calories.  This could well be because the fruit was served last, when the children’s plates were almost full.

Now for the juicy part.  The children didn’t eat everything they served themselves, and for every extra calorie served with the big plates, they only ate .43 calories- so 57% of the extra food was simply wasted.  Also, how much they liked the food had more than twice as much of an effect as plate size- liking all 3 dishes lead to serving themselves an extra 210 calories, while using adult sized dishes only lead to a 90-calorie increase in food served.

Finally, the study found that children who suffered from food insecurity (i.e. poverty) were more affected by plate size, while gender and BMI had no effect. 3

In a separate 2013 study by Penaforte et al, adult college students were asked to estimate the size of a 400g serving of pasta on either a large or small plate, as well as to subjectively classify it as either small, medium or large.  The average estimate was higher when the pasta was displayed on a large plate vs a small plate, though the amount fell just short of statistical significance.  What did reach significance: subjects were twice as likely to rate the portion as “large” when it was on a large plate. 4

Also notable was that overall, the subjects underestimated the portion size by downright comical margins regardless of plate size.  The average guess was 150 grams with a large plate and 115 grams with a small plate- remember, the correct answer was 400 grams!

A 2014 meta-analysis found that the effects of plate size depend on a wide variety of factors, including distraction, type of container used, whether people were serving themselves or served by someone else, and the type of food used. 

An experiment performed by the same team in conjunction with the meta-analysis found that plate size had no significant impact on total energy intake, but that using larger plates caused people to eat more vegetables, particularly when those vegetables were served as side dishes.  The researchers concluded that using smaller plates was ineffective at reducing total caloric intake, and that in fact using larger plates may well be an easy way to increase vegetable consumption. 5

The real skinny on plate size: Key takeaways

All of that is a lot to take in, but it can be boiled down to a few simple recommendations:

  • If you’re making a serious effort to diet and control your portion sizes, plate size doesn’t seem to matter.  It might matter if you’re having a cheat meal, but only if you’re serving yourself, and even then, you may actually be better off with a large plate if the meal includes vegetables.
  • The plate size illusion can work in reverse too- if you don’t finish your food, a larger plate could make the unfinished portion seem smaller, causing people to eat less, particularly if they’ve been raised to believe they shouldn’t waste food.
  • When serving yourself, serve vegetables onto your plate first, then meats, then fruit.  Save high-calorie/low-nutrient dishes like pasta for last.
  • While plate size isn’t very useful for controlling your own food intake, it might be useful for controlling other people’s food intake- as a parent, restaurant/cafeteria manager, or public health professional.
  • You probably suck at visually estimating how much food you’re looking at.  Instead of eyeballing, specifically measure how much food you’re eating- either by eating foods like chicken nuggets that are divided into discreet units, or by carefully measuring food out with a serving spoon.  Look at how people serve out precise amounts of each ingredient at fast food places like Chipotle- copy that practice at home.
  • How much you like your food is waaaay more important than hack-y tricks like plate size.  Learn to cook healthy food, especially veggies, so they taste good.
  • Learn to read scientific studies, and be very skeptical of them.  Familiarize yourself with some of the problems in the scientific community, like agreement bias, data fraud, and the replication crisis. 

On the whole, the research doesn’t support the notion that using smaller plates will help you lose weight.  Are there hacks you can use to trick yourself into losing weight?  Sure, depending on what you consider to be “tricking.”  But this isn’t one of them.

*Math note: 12-inch plates sound just slightly larger than 10-inch plates, but they’re not.  Those numbers represent diameter, and area = π x r2, so a 10-inch plate has an area of 25π inches, while a 12-inch plate has an area of 36π inches- a full 44% larger.

References

1.  Van Ittersum, Koert, and Wansink, Brian (2012)  Plate Size and Color Suggestibility: The Delboeuf Illusion’s Bias on Serving and Eating Behavior.  Journal of Consumer Research, Vol. 39 No. 2

2. Wansink, Brian; Van Ittersum, Koert (2013). “Portion Size Me: Plate Size Can Decrease Serving Size, Intake, and Food Waste”. Journal of Experimental Psychology: Applied19 (2): 320–332.

3.  DiSantis et al (2013) Plate Size and Children’s Appetite: Effects of Larger Dishware on Self-Served Portions and Intake. Pediatrics, Vol 131 / Issue 5

4. Penaforte et al (2013) Plate size does not affect perception of food portion size. Journal of Human Nutrition and Dietetics, Volume 27, Issue s2

5. Libotte et al (2014) The influence of plate size on meal composition. Literature review and experiment.  Appetite, Vol 82