Why Do We Overeat?

Feb. 16, 2001 -- Sixty percent of Americans are overweight and one quarter are obese — at least 20 pounds too heavy. Scientists are now making strides in figuring out why Americans eat too much.

Quiz Yourself: Surprising Factors That Cause Overeating

It's not that food tastes better than it used to, and it isn't just that we can afford more. Scientists have discovered that many environmental factors cause overeating. Penn State University professor Barbara Rolls describes these factors in her book, Volumetrics.

Rolls and her colleagues examined the eating habits of 3-year olds and their studies show they have an innate ability to listen to their bodies. Even when they were served massive amounts of food, they ate just the right amount to meet energy needs and left the rest.

Then the scientists repeated the experiments with 5-year olds. The older children kept eating past the normal satiation point. Rolls explains that between the ages of 3 and 5, kids start paying attention to the factors other than hunger that affect eating.

"The 5-year olds are really responding to the portion size, rather than listening to their bodies. This is probably influencing us through the rest of our lives," says Rolls.

Eating Because It's There

University of Illinois professor Brian Wansink demonstrates the power of portion size in an experiment in which he invites test subjects to eat soup. Unbeknownst to the subjects, two of the four bowls are continually refilled through concealed tubes. The test subjects with the rigged bowls end up eating as much as 70 percent more than the others.

Rolls explains that eating is not just about hunger. "I don't think most of us are eating when we're hungry. I think we're eating because the food is there," she says.

Eating Under the Influence

But portion size is not the only factor causing people to overeat. Take thisquiz to see if you can guess how other factors can influence your eating habits.