The steady growth of food portion sizes served both in restaurants and at home encourages the overeating that is fueling the obesity epidemic in the United States, according to a survey by the American Institute for Cancer Research.

In a survey of more than 1,000 adults, the organization found that Americans know little about appropriate food portions, and have lost sight of the relationship between the size of the portions they eat and their weight.

When researchers asked the survey participants to estimate the standard serving sizes for eight common foods like green beans, nuts, mashed potatoes and cereal, six in 10 participants missed four or more. Seven percent were only able to answer one question correctly.

But with portion sizes at a record high, the researchers said that seven in 10 Americans now say that when they go to a restaurant, they finish their entrees most or all of the time -- a 2 percent increase since 2000.

The number of women who say they finish their entrees every time they eat out has doubled from 9 percent to 18 percent in the past three years.

"And what they're doing in restaurants is spilling over into their homes," said Barbara J. Rolls, a nutrition researcher at Pennsylvania State University. She said the portion sizes that people see in restaurants comes to "look normal to them."

"Rresearch indicates that everyone -- men and women, those at a healthy weight and those who need to lose a few pounds -- is susceptible to the influence of portion size," Rolls told a news conference.

Other sources: American Institute for Cancer Research