It happens every year. It's not that you resolve to be virtuous on Thanksgiving, just reasonable. Two plates of food, and no more. One piece of pie, and that's enough. But when you're sitting at that table, staring at that food, there is no more self-control. No more reasonable. You stop when you can hardly breathe.
Or maybe I'm projecting. This column, however, will not be about exercising self-control at the table. It's Thanksgiving! Rather, this column will be about something far more powerful: exercising some economic principles.
For a long time, economists operated under the "rational actor model." Human beings were thought to be rational creatures who correctly weighed costs and benefits and calculated the best choices for themselves. Then some economists met some human beings and realized we don't really work like that. The result has been the rise of "behavioral economics," which attempts to build the responses of actual human beings into its models.
MIT economist Dan Ariely is a pioneer in the field. His bestselling book "Predictably Irrational" is as good an introduction to the discipline as you'll find. Human beings, he argues, aren't just irrational: They are irrational in predictable ways and in predictable circumstances. That means we can plan for that irrationality beforehand, when we're still feeling rational.
I asked Ariely how he would set up his Thanksgiving feast to limit overeating without having to exercise self-control. His answer was to construct the "architecture" of the meal beforehand. Create conditions that guide people toward good choices, or even use their irrationality to your benefit.
"Move to chopsticks!" he exclaimed, making bites smaller and harder to take. If the chopsticks are a bit extreme, smaller plates and utensils might work the same way. Study after study shows that people eat more when they have more in front of them. It's one of our predictable irrationalities: We judge portions by how much is left rather than how full we feel. Smaller portions lead us to eat less, even if we can refill the plate.
Speaking of which, Ariely suggests placing the food "far away." In this case, serve from the kitchen rather than the table. If people have to get up to add another scoop of mashed potatoes, they're less likely to take their fifth serving than if they simply have to reach in front of them.
"Start with a soup course," he says. That is what economists refer to as a default: Rather than putting everything on the table for people to choose, you begin by making the choice for your guests. If the first course is relatively filling and relatively low in calories, everyone will eat less during the rest of the meal.
Indeed, it's not a bad idea to limit the total number of courses. Variety stimulates appetite. As evidence, Ariely brings up a study conducted on mice. A male mouse and a female mouse will soon tire of mating with each other. But put new partners into the cage, and it turns out they weren't tired at all. They were just bored. So, too, with food. "Imagine you only had one dish," he says. "How much could you eat?"
What you eat, of course, is also important. Studies show that people aren't very consistent in the amount of calories they eat each day, but they're very consistent in the volume of food they eat each day. Thanksgiving is an exception to that consistency, but probably not to the underlying rule. Satisfaction doesn't depend on caloric intake; low-calorie, high-fiber foods and foods high in water content are filling. Thus, the more broccoli rabe there is at the table, the better.
Speaking of which, take a page out of the pilgrims' book and make sure all the food at the table was cooked by someone in the house. Economists believe that the obesity epidemic is largely attributable to the rise in food we don't make for ourselves. In 1900, it was hard to snack on potato chips because it was time-consuming for a member of the household to make potato chips. Today, of course, things are different, and there is a surfeit of vending machines and drive-throughs and supermarkets. But on Thanksgiving, make like you're in Plymouth, and ensure all of the food is homemade. There will be fewer calories available if Grandma's stuffing isn't supplemented with bowls of chips and cheese.
For all that, Ariely's main advice is not to worry too much about Turkey Day. "I don't think Thanksgiving is a time to watch your diet," he says. "How many calories can you put away in a day? Maybe 5,000 or 6,000 calories, if you really try hard." The problem, he says, is another human irrationality: remembering to pay attention to the season's big meals but not the everyday ones in between. The solution to overeating, Ariely says, "comes from [making] small changes across many normal meals."
That seems rational. But if you insist on trying to cut back at Thanksgiving, Ariely does have one more piece of advice: "Wear a very tight shirt."
This column was first published in November 2009.