Conducted by researchers at the University of Pennsylvania, the study suggests that people are affected by their environment when deciding how much to eat.
The new findings come as no surprise in a nation where portion sizes have been repeatedly blamed for the rising obesity rates. Indeed, previous research has shown that portion sizes of restaurant foods and processed products have continued to increase since the 1970s.
The new research, published in the June issue of the journal Psychological Science, examines the concept of ‘unit bias’, or the idea that a single food portion is the appropriate amount to consume.
According to the researchers, this is a general feature in human choice.
“Unit bias explains why small portion sizes are effective in controlling consumption; in some cases, people served small portions would simply eat additional portions if it were not for unit bias,” they write.
The research study
In order to test their theory, the researchers placed bowls of different sized Tootsie Rolls and Pretzels in an office building and an upscale apartment building. They also placed bowels of M&Ms with different-sized serving spoons. Results were collected during a period of between 10 days and 12 weeks.
In general, on days when larger portions were available, people would consume more of each product.
However, the researchers also noted that because the number of large units consumed were not equal to the number of small units consumed, factors other than unit bias also influenced consumption.
These could include social reasons specific to the conditions of the study, such as a desire not to appear greedy.
The researchers also noted that further work needs to be done to clarify the conditions under which unit bias operates.
Call for uniform portion sizes
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. - (Decision News Media, August 2006)