Cover Story

It's not your imagination that your favorite restaurant has been serving up larger amounts of that incredible pasta dish. Research shows that portion sizes--of restaurant foods, grocery products and even the servings suggested in cookbook recipes--began to swell in the 1970s and have grown ever since. The phenomenon is easiest to spot with fast-food products that audaciously trumpet their volume--Wendy's Great Biggie Fries, 7-Eleven's Extreme Gulp and Frito Lay's Big Grab Bag, to name a few.

Portion size is big on obesity experts' minds. While no one has been able to prove a causal link between the trend and our nation's weight problem (see page 46), there are enough clues to suggest it's a culprit.

"The food industry creates and prices portion sizes to maximize food intake," maintains Yale University psychologist and obesity expert Kelly Brownell, PhD, who writes about the issue in his new book "Food Fight: The Inside Story of the Food Industry, America's Obesity Crisis and What We Can Do About It" (McGraw-Hill, 2003). "That's no surprise--it's their business--but the consequence is a lot of overeating."

Brownell adds that the big-portions trend demonstrates the convergence of two uniquely American forces: the importance that Americans place on value and marketers' capitalizing on this tendency. If it takes a nickel to produce the extra popcorn that goes into a large- versus a medium-sized popcorn, and the large size costs the consumer 39 cents more, Brownell explains, the food vendor reaps a large profit while appearing to offer a great deal.

Researchers are using a variety of techniques to study the effects of portion size. In a literature review in the March/April 2003 issue of Nutrition Today (Vol. 38, No. 2), Barbara J. Rolls, PhD, a nutrition expert at Pennsylvania State University and co-author, with Robert A Barnett, of "The Volumetrics Weight-Control Plan" (Quill, 2000; HarperTorch, 2003), summarizes research findings that:

  • We eat more when we're given more.

  • Package size influences us to eat more.

  • We don't compensate for eating too much at one sitting by eating less at the next.

  • Having access to big portions can override our natural sense of fullness.

Bigger packaging means more consumption

In a 2002 article in the American Journal of Clinical Nutrition (Vol. 76, No. 6), for example, Rolls and her team gave 51 people four different portion sizes of macaroni and cheese on different days. The bigger the portion size, they found, the more people ate--30 percent more calories when given the biggest compared with the smallest portion.

The investigators also asked participants to rate feelings of hunger and fullness after the meals. No matter what portion size they ate, their ratings were similar, suggesting that people adjust or mask their natural feeling of fullness to accommodate greater food availability.

In a similar 2001 study reported in Food Quality and Preference (Vol. 12, No. 1), marketing expert Brian Wansink, PhD, who directs the University of Illinois' Food and Brand Lab, and Se-Bum Park, a doctoral student in marketing at Northwestern University, randomly assigned 139 theater-goers of all ages a medium or large size of popcorn and found, as Rolls did, that those who got the bigger size ate more than those who got the smaller size. What's more, those who rated the popcorn unfavorably ate even more than those who rated it favorably--61 percent more, compared with 49 percent more.

The results led him to consider the possibility that package size subliminally influences how much of a product we use. Other studies he's conducted have nailed the point. In one, people used more laundry detergent per load when given a bigger container, and in another, they poured more dog food into their dog's bowl when the package was bigger.

Land of the overweight?

America's unique niche in the outsize-portion area is illustrated by a study reported in the September issue of Psychological Science (Vol. 14, No. 5) by University of Pennsylvania psychologist Paul Rozin, PhD, and colleagues. Comparing 11 pairs of equivalent eateries in Paris and Philadelphia--including fast-food chains, pizzerias, ice-cream parlors and ethnic restaurants--the team found that mean portion sizes in Paris were 25 percent less than in Philadelphia. The study, while simple, was important to conduct because it hadn't been done before, says Rozin.

"Everyone who goes to Europe notices these things," says Rozin, who's well known for his cross-cultural research on the social role of food. The findings suggest one reason why the French may keep relatively slim compared with Americans, despite regularly consuming fat-rich foods like croissants and brie, he says.

Problematically, notes Rolls, the notion of portion size gets contorted in this country because while there actually are healthy rules about portion sizes--the U.S. Department of Agriculture's suggested serving sizes--few people have a realistic clue of what those are.

Plans of attack

A variety of strategies may help to address the portion-size problem, researchers believe, including consumer-awareness campaigns and advocating for better food labeling.

Another possibility is asking people to change what they eat a lot of. Research shows that learning to substitute food volume for food density can help people lose weight in a more satisfying way than by restricting the amount they eat.

In her "Volumetrics" book, for example, Rolls provides practical ways people can do this in their daily lives, such as by adding more lettuce and tomato to hamburgers and reducing the amount of meat. In essence, "People should be eating satisfying portions of foods low in energy density such as fruits and vegetables, whole grain and lean protein," she notes. "If they do this, they won't have to worry so much about portion size."

Food companies could help too, Wansink says. Adding more air or low-fat fillers to a product could be a winning strategy for consumers and companies alike, reducing company costs and saving consumers the extra weight, he says.

"You could cut the calories of a Snickers bar by 10 or 15 percent and no one would know the difference," he says. Others, like Brownell, suggest campaigns to get food manufacturers to reduce actual portion sizes.

Tori DeAngelis is a writer in Syracuse, N.Y.