The Clean Plate Habit
Experts agree that the "clean your plate, no matter what" habit is very powerful.
"We have performed studies that show that people tend to always put the same amounts on their plates even when plate sizes vary," David Levitsky, PhD, professor of nutrition and psychology at Cornell University, says in an email interview. "In part it is habit, a factor that is difficult to change."
Further, "the environment is a complete setup that conspires against reasonable-sized portions," says Kelly Brownell, PhD, director of the Rudd Center for Food Policy and Obesity at Yale University.
For example, consider food prices, says Brownell: "Prices are usually better for larger portions, which play into people's obsession with value -- they care about quantity vs. quality."
Schwartz notes that both our biology and the environment are working against us.
"There are many variables that influence how much we eat that operate at a completely unconscious level," says Schwartz. "People eat more when they are eating with more people, when they stay at the table longer, when there is more variety in what is served, when the food is physically closer to us, and when the food is easier to access."
So would we be more likely to eat reasonable portions if we tried to work against these factors – say, if we cleared the table quickly and visited after the meal instead of during it; limited the variety within our meals; and kept serving plates in the kitchen instead of on the dinner table? Schwartz thinks so.
How to Get Started
Schwartz likens eating healthfully in our current environment to a part-time job that requires knowledge, time, energy, and constant vigilance.
"It's not reasonable to expect an entire population of people to do this," says Schwartz. "We need to change the environment so the healthy behavior is the automatic, default behavior, not the one that requires work."
Levitsky believes people need to see the positive consequences of reducing portion sizes. His research has shown that one such motivation is weight loss. "If people monitor their weight daily they can see the changes occur within a couple of days," he says.