Published in this month's issue of the Journal of the American Dietetic Association, the study was designed to provide an up-to date version of similar research conducted 20 years ago.
And according to the researchers from Rutgers University, consumers today are increasingly experiencing 'portion distortion'.
"Portion sizes of virtually all foods and beverages prepared for immediate consumption have increased over the last two decades… Consumers now perceive these larger portion sizes as the appropriate amount to eat at a single eating occasion, thus experiencing portion distortion," said the researchers.
Following the format of a similar study conducted in 1984, the latest study was designed to determine current portion sizes typically chosen by young adults, and examine how these compare with the reference amounts based on the 1984 Nutrition Labeling and Educations Act.
Participants in the study were college students ranging in age from 16 to 26, who were asked to serve themselves 'typical portion sizes' at breakfast, lunch and dinner from a buffet food bar.
The amount of each food chosen was then "unobtrusively" weighed without the participant realizing, by weighing what was left in the serving bowl.
The researchers found that typical portion sizes of foods such as jelly, milk on cereal and cornflakes tended to exceed reference portion sizes by more than 25 percent.
But typical portion sizes of butter, tuna salad, tossed salad and salad dressing tended to be more than 25 percent less than reference portion sizes. This could be a result of efforts to educate the public to limit certain foods that have the potential to contribute excess energy, said the study.
But in general, according to the researchers, "the general lack of awareness among participants of how their typical portion sizes compare with reference sizes may affect nutritional health."
And part of the reason for this lack of awareness are the portion sizes people have become used to in foods sold in the marketplace, which often contain more than one portion in a single unit package.
"To 'undistort' typical portion sizes, policymakers could refine Nutirition Facts labels to make the number of servings in a single container more prominent and to fund a consumer awareness campaign to highlight the parallel relationship between increasing portion size and body weight," wrote the researchers.
"Policymakers could also (…) urge food manufacturers to make foods and beverages in single-unit containers equal to one serving."
The new study follows calls last year by the Grocery Manufacturers Association (GMA) to implement uniform portion size standards on all processed food packaging. "Consumers do not always link caloric content to the serving size listed," said GMA senior director of nutrition and regulatory policy Alison Kretser.
"Some simple changes to the Nutrition Facts Panel could help consumers make smarter dietary choices."
Indeed, the 2005 Dietary Guidelines Advisory Committee (DGAC) guidelines, which former USDA secretary Ann Veneman claimed were designed to "address the epidemic of overweight and obesity," specifically targeted portion size as a key determinant in what people eat. The DOAC decided that portion control was of such concern that it devised a new pyramid model using the leanest form of every food product category.
And the contention that portion size plays a significant role in dictating food intake was also confirmed by another study conducted last year by Barbara Rolls, holder of the Guthrie chair of nutritional sciences and director of the Laboratory for the Study of Human Ingestive Behavior.
The study found that when served larger portions for an extended period of time, people consumed more food over the entire period.