Nation & World

Why we eat too much

Almost 20 years ago, psychology professor and biologist Paul Rozin tested a theory about food. Many people thought their bodies were good at telling them when to start and stop eating, but he wasn’t so sure.

“A lot of things that control what and how much people eat have nothing to do with the state of nutrition,” Rozin told The New York Times in 1998.

His experiment, published in the journal Psychological Science, was simple but ingenious. He worked with two severely amnesic patients whose memories had been damaged by illness and who had difficulty recalling things that happened more than a minute before. He fed them a meal; at least 10 minutes later, he fed them another. And at least 10 minutes after that, he fed them a third. He repeated the experiment on three occasions, and each time the same thing happened: they eagerly ate the food that was served to them. One of the participants even announced, after having a third lunch, that he planned to “go for a walk and get a good meal.”

The part of the patients’ brains that triggered satiety and hunger didn’t seem to function without the patients actually remembering having eaten.

Memory is just one of the subtle but powerful factors that affect eating habits. Some of these are simple and fairly straight forward, like the size of the plates we use, which have been shown to change how much we eat, or the presence of a television, which has been shown to do the same.

But other influences are far less obvious. A recent peer-reviewed study found that something as innocuous-seeming as the size of a table can affect how people perceive the food placed in front of them — the larger the table, the harder it is for people to discern that they have been served less food, and the more easily they are satiated.

Subtle social cues are impactful, too. A separate study, published last month, found that diners who were served by overweight waiters tended to “order significantly more items.”