According to the Associated Press, the researchers were curious to see whether limiting one's tendency to overeat -- which results in part from your body's gut reaction to seeing food on the plate -- may be curbed if the portions for the often starchy side dishes are smaller. Restaurants "pile on" the sides, they note, because it's a cheap way of filling the plate to give you the illusion that you're getting a great deal. Even if you can't actually eat it all.
The researchers tested their theory on 970 lunchtime customers at a "popular Chinese franchise" at Duke where customers choose a side of rice or noodles before picking their main course. The standard serving size for each side is 10 ounces and has 400 calories.
After the customer picked their calorie bomb, they were asked if they would rather have a half-size portion of their side "to save 200 calories." Depending on the customer mix and the day of the week, 14 to 33 percent of those asked opted for the half-order. And those customers "didn't order a higher-calorie entrée to compensate" for their lower-calorie side dish. The researchers also weighed the food thrown away after the meal and found that those who picked the smaller portion "threw away the same amount of food as customers who refused or weren't offered the option."
Neither a 25-cent incentive discount in the price of the smaller portion nor calorie count labels (which is mandatory in California) affected the customers' decisions, prompting the researchers to conclude that the half-order offer at the beginning of the point of sale made a crucial difference.
These results are consistent with Cornell food science researcher Brian Wansink's studies on how our perceptions affect our consumption. He found, for example, that using a 10-inch plate as opposed to an 11-inch one encourages people to serve themselves a smaller amount of food, and that the smaller dish makes "normal serving" sizes "look more satisfying." In another study, he discovered even the plate color makes a difference: People "served 18 percent more pasta with marinara sauce onto a red plate than a white one - and 18 percent more pasta alfredo onto a white plate."
Ultimately, selling this idea of the half-portion is an issue of semantics, a topic Malcolm Gladwell discussed at length on why McDonalds's McLean failed ("Who goes to McDonalds for healthy food?"). Ariely suggests calling these half-portion options "right-sizing" as opposed to "downsizing." After all, who goes to Panda Express for downsized chow mein?