NEWARK, N.J. — Along with the American waistline, the American plate and portion size have grown, too. A study at Rutgers University supports earlier research that people today eat bigger servings than they did 20 years ago.

"People aren't realizing how much they are eating," said Jaime Schwartz, a registered dietitian and one of the authors of the study. "The larger portion size they're eating — even if it's a healthy food — is still more calories."

The research, done in 2003 and described in a recent issue of the American Dietetic Association, replicated a 1984 Penn State University study.

Both studies asked students to take food portions of various items. Diners were offered three sizes of plates, bowls and cups in a buffet-like setting.

In a comparison of breakfast servings, the students in 2003 took 20 percent more cornflakes than students took in 1984, Schwartz said. Ditto for milk. The glass of orange juice grew by more than 40 percent compared to 20 years ago. That translates into 50 additional calories, or a weight gain of 5 pounds over the course of a year, if consumed on a daily basis. Dinner and lunch servings grew, too — 50 percent more fruit salad wound up on the plates of the Rutgers students.

"People are eating with their eyes and not their stomachs," Schwartz said. "They're not listening to their bodies to tell them when to put the fork down."

Helen Guthrie did the original Penn State study when she couldn't get accurate self-reported data on how much food people ate because they wrongly estimated portions. That's when she set out to see if diners could visualize portion size. Most people still lack that skill, but the portion size is getting larger, said Guthrie, a professor emeritus.

A 1994 informal survey found that the standard plate size in the restaurant industry grew in the early 1990s, from 10 inches to 12.

"That holds 25 percent more food," Schwartz said. "That really makes a difference in how much our plates can hold and how much we eat from them."