2005 Annual Meeting Tuesday Highlights: Putting Portions into Proportion

- When it Comes to Food, Size Matters -

Vancouver, British Columbia - October 19, 2005 The link between portion size and excess energy intake has been well established in the scientific literature, and several studies note a parallel increase in rates of obesity and increasing portion size. Findings to be presented today at the 2005 Annual Scientific Meeting of NAASO, The Obesity Society, offer new perspectives on how and why people overeat when served large amounts of food as well as provide potential strategies to reverse this trend.

Does Portion Size or Amount of Food Affect Consumption? (138-OR; 8:15 a.m. PT)

Snacking on foods packaged as individual servings does not appear to lead people to eat less than eating the same food out of a large bag. This suggests that the total amount of food available, not the package or portion size, provides the cue for how much to eat.

"Consumers might think they will eat less by purchasing pre-packaged quantities of individually sized snacks rather than one bigger bag or box. However, our study suggests this is not the case," said Hollie Raynor, Ph.D., R.D., assistant professor of research at Brown Medical School and Miriam Hospital in Providence, RI. "Additionally, portion-controlled packages are often more expensive than large packages."

In the study, 28 healthy, college-aged, non-obese volunteers who were not dieting or trying to lose weight were randomly assigned one of four boxes of snack foods (potato chips,cookies, cheese crackers and candy) with either large or small portions and a large or small total amount of food. The four box conditions were single-serving bags totaling 4,350 kcal or 8,750 kcal, or large portions (at least five times the size of the single-serving size) totaling 4,350 kcal or 8,750 kcal. Thus, participants in the two small amount conditions received the same amount of food, but it was packaged differently, and the same was true for the two large amount groups. Participants took the food home, ate as much or little as they wanted and brought back any remaining food after three days.

The results showed that all participants ate approximately 60 percent of what was given to them, regardless of how it was packaged. The subjects who took home the 4,350 kcal boxes ate the same total amount of snack food over three days whether the food was packaged as individual servings or as large bags. The same was true of the two groups receiving the 8,750 kcal boxes. Additionally, the two groups with the large amount of food consumed about 80 percent more energy over the three days, an average of 5,028 kcal vs. 2,782 kcal for those who got the smaller total amount of food. These findings indicate that smaller portions did not influence how much to eat. Rather, the total amount supplied suggested the appropriate amount.

The Effect of Increased Portion Size on Energy Intake is Sustained for 11 Days (139-OR; 8:30 a.m. PT)

When served larger portions for an extended period of time, people consume more food over the entire period, suggesting the body's biological signals for controlling hunger and fullness do not step in to regulate intake.

With rates of overweight and obesity on the rise, Barbara Rolls, Ph.D., set out to determine if larger portions could be a driving force behind the obesity epidemic. Other research has shown that since the 1970's portion sizes of restaurant foods, grocery products and recipes in cookbooks have continued to increase. Dr. Rolls' new study, the longest look at the sustained effect of increased portion size, builds on her earlier work demonstrating the same effect over a short period of time.

"Living in the age of supersize meals and 'huge food,' our study shows that there is a great need for people to be more aware of what and how much food they are served. Consistently being presented with bigger portions can have a sneaky effect on energy intake, even for people who don't regularly clean their plates," noted Dr. Rolls, professor of nutritional sciences at Penn State University in University Park, PA.

In the study, 23 normal weight and overweight adults were provided all of their meals (food and beverages) for two 11-day periods with a two-week break in between. During one of the 11-day periods, standard portion sizes were served of a menu that changed daily. During the other period, the same meals were served, but all of the portions were increased by 50 percent. The order of the periods was randomized across participants, and all meals were consumed in the laboratory, except on the weekends, when participants took the food home.

At the end of the study, the subjects consumed an average of 16 percent more calories per day - or an extra 4,500 calories over the 11 days - during the large portion period. The effect was sustained over the entire period and did not decline over time. Additionally, the participants experienced a slight decrease in hunger and slight increase in fullness over the 11-day period of large portions, but this did not modify the effect of portion size on intake.

The extra calories consumed in this study translate to a weight gain of approximately 1.25 pounds, assuming no other factors important in weight regulation are changed (e.g., increasing exercise). Participants in this study were not informed about the change in portion size; thus, they were not trying to compensate for eating more food. Interestingly, only about two-thirds of the study participants noticed the change in portion size.

According to Dr. Rolls, the combination of bigger portions and calorie-dense foods is a dangerous one, and people should not feel compelled to clean their plates. Some strategies she suggests to control portion size while eating out are ordering an appetizer rather than an entrée, sharing the main course and bringing home a doggie bag.

Effects of Age on Children's Intake of Large and Self-Selected Portions (140-OR; 8:45 a.m. PT)

The observation that individuals are susceptible to consuming more calories when offered a large portion of food compared to a standard portion may start in children as young as two years old, according to results from an experimental study. The age at which this phenomenon occurs has been debated in the pediatric nutrition community, with previous research suggesting this effect does not occur until the preschool years.

"Our work indicates that eating behavior is influenced by environmental factors such as portion size from a very young age," said Jennifer Orlet Fisher, Ph.D., assistant professor in the department of pediatrics at Baylor College of Medicine in Houston, TX and a researcher for the USDA Children's Nutrition Research Center, which funded this study. "To help counter this behavior, parents can involve their youngster in portion size selection, which seems to encourage more age-appropriate intake."

The researchers served 75 non-Hispanic white children, age two to nine years old, a dinner meal on three different occasions. The meal consisted of macaroni and cheese, corn, applesauce, carrots, cookies and milk. The macaroni and cheese portions were varied at each meal and were either age-appropriate, doubled in size or determined by the child after helping him/herself from a serving dish containing the double-sized portion.

On average, the children did not finish the age-appropriate sized portion, consuming just over half of it (56 percent). Yet, when served the large portion, the children ate 29 percent more and increased energy intake by 13 percent. The effect was consistent across all ages. The increase in consumption was attributed to the children taking larger bites, rather than more bites, indicating that the amount of food provided a subtle visual cue of how much to eat.

In an analysis of the children who ate more of the large portion than the reference portion, the researchers discovered that the children ate less when they served themselves.

Overweight and obesity has reached epidemic proportions in the United States, as well as worldwide. Data collected by the National Center for Health Statistics indicate that the prevalence of obesity, defined as a body mass index >30 kg/m² has increased from 12.8% in 1976-1980 to 22.5% in 1988-1994 and 30% in 1999-2000. Roughly 31% of American adults meet the criterion for obesity - about 59 million American adults. More than 64% of the US adult population have a BMI >=25 kg/m². In the past 30 years, the occurrence of overweight in children has doubled and it is now estimated that 16 percent of children in the US are overweight. Increases in the prevalence of overweight are also being seen in younger children, including preschoolers. Also, while more children are becoming overweight, the heaviest children are getting even heavier. As a result, childhood overweight is regarded as the most common prevalent nutritional disorder of US children and adolescents, and one of the most common problems seen by pediatricians.

NAASO, The Obesity Society, is a leading scientific society dedicated to the study of obesity. NAASO is committed to encouraging research on the causes, treatment and prevention of obesity as well as to keeping the scientific community and public informed of new advances in the field. For more information about NAASO and obesity, visit www.naaso.org or call (301) 563-6526.