Constant Cravings

What keeps us from eating all day isn't how full we'd feel, it's our memory of already having eaten.

By Camille Chatterjee, published on July 1, 1999 - last reviewed on December 22, 2005

Chocolate ice cream, macaroni and cheese, Mom's meatloaf: we all
have foods we crave, we could eat them all day. But what
keeps us from doing so isn't how full we'd feel. It's our memory of
already having eaten.

Paul Rozin and colleagues hoped to determine why we sit
down to meals when we do. Is it because we're physiologically hungry? Or
because we're mentally aware of not having dined for a few hours?

Rozin, a professor of psychology at the University of Pennsylvania,
and his team recruited two patients who were densely amnesic, meaning
that they had virtually no memory of events that had happened more than a
minute ago. First, the researchers placed a meal that the subjects
professed to enjoy (a Swanson TV dinner for one, cheese-rice casserole
for the other) in front of them. When the patients had finished eating,
their plates were taken away and they were asked to sit and chat with the
researchers. Between 10 and 30 minutes later, Rozin asked if they wanted
a meal. Both memory-impaired subjects readily accepted the second
lunch -- and even a third meal. Before the second and third meal, the two
men only vaguely recalled that they'd eaten earlier, and couldn't say
what they'd consumed or when it had been. In fact, 20 minutes after
eating much of his third lunch, one subject claimed that he'd like to "go
get a good meal." Two control subjects without global memory deficits,
however, ate only the first lunch offered and were genuinely surprised
and puzzled when asked if they wanted a second.

This finding, says Rozin, suggests that what keeps us from eating
constantly isn't a lack of hunger, but our knowledge that we just ate. So
without our culturally determined three meals a day, we'd likely be
content to snack around the clock.