A Penn State study has shown that bigger restaurant portions lead to higher calorie intake. In addition, a related laboratory study demonstrated that, when portion sizes of all foods served over a two-day period were increased, individuals continued to eat more at each main meal – in other words, they didn't compensate for overeating the first day by cutting back at meals the next day.
Dr. Barbara Rolls, who holds the Guthrie Chair of Nutrition in Penn State's College of Health and Human Development, led the studies. She says, "The bigger portions that restaurants are providing make consumers vulnerable to overeating, since most individuals eat all or most of what is served. The excess food in megaportions is not going home in doggie bags. It is, instead, fueling the obesity epidemic."
Nicole Diliberti presented the results of the restaurant study and Tanja V. E. Kral detailed the two-day intake study today (April 12) at the Experimental Biology (EB) 2003 conference in San Diego, Calif. Both are graduate students in nutrition under Rolls's direction.
Diliberti says that in the restaurant study, on different days, the size of the baked ziti portion served at a cafeteria-style restaurant was varied between a standard portion and a larger serving containing 50 percent more. The price for the meal, which included a pesto-stuffed tomato and a roll and butter, as well as the ziti, remained the same. Customers who ordered the meal were also asked to rate their satisfaction and the appropriateness of the portion size. In addition, their food intake was measured by weighing each entrée in the kitchen before and after the meal.
The results showed that when customers were served 50 percent more ziti, they ate nearly all of it or an average of 172 more calories. The survey responses showed that the diners rated the size of both portions as equally appropriate.
The two-day intake study, reported by Kral, was conducted in Penn State's Laboratory for the Study of Human Ingestive Behavior. There, 32 men and women ate breakfast, lunch and dinner, and were given take-out snacks and water for between meals, on two consecutive days for three weeks. Each week, the same two daily menus were served but the portion sizes of all foods were varied.
When portion sizes were 50 percent larger, the women ate 335 more calories per day and the men ate 513 more. When the portion sizes were doubled, the women ate 530 calories more per day and the men 803 more. It didn't matter how much they had eaten the day before. Given more food, they ate more. They didn't compensate on the second day for having overeaten the day before.
Diliberti's paper is titled "Increasing the Portion Size of a Restaurant Entrée Results in Increased Food Intake." Her co-authors are Dr. Peter L. Bordi and Dr. Martha T. Conklin of Penn State's School of Hotel, Restaurant and Recreation Management and Rolls.
Kral's paper is titled "Effect on Food Intake of Increasing the Portion Size of All Foods Over Two Consecutive Days." Her co-authors are Jennifer S. Meengs and Denise E. Wall, research technologists, Liane Roe, research nutritionist, and Rolls. Both studies were supported by grants from the U.S. National Institutes of Diabetes and Digestive and Kidney Diseases of the U.S. National Institutes of Health.