The observation is one more indication of broad changes in the way Americans eat and another reason for the widespread, unhealthy rise in obesity among U.S. children and adults, University of North Carolina at Chapel Hill researchers say. It is believed to be the first documentation that at any given meal, on average, the typical American eats more than he or she did only a few decades ago.
A report on the findings appears in Wednesday's issue (Jan. 22) of the Journal of the American Medical Association. Authors are doctoral student Samara Joy Nielsen and Dr. Barry M. Popkin, professor of nutrition at the UNC schools of public health and medicine and a fellow at the Carolina Population Center.
"Many people have thought that portion sizes might be on the rise, but until now, there have been no empirical data to document actual increases," Nielsen said. "We think this is important information not only because it documents this trend, but also because obesity presents a growing health threat both in the United States and abroad."
The research involved analyzing nationally representative data from the 1977-78 Nationwide Food Consumption Survey and three separate Continuing Surveys of Food Intake by Individuals. The sample consisted of 63,380 people ages 2 and older.
Nielsen and Popkin calculated the average amounts of specific foods eaten in both calories and ounces at home, in restaurants and in fast-food restaurants for each survey year.
"Portion sizes varied by food source, with the largest being consumed at fast-food establishments and the smallest at restaurants," she said. "Between 1977 and 1996, portion sizes increased for salty snacks, desserts, soft drinks, fruit drinks, French fries, hamburgers, cheeseburgers and Mexican food."
Such increases were large, Nielsen said.
"The quantity of salty snacks increased by 93 calories or 0.6 ounces, soft drinks by 49 calories or 6.8 ounces, hamburgers by 97 calories or 1.3 ounces, French fries by 68 calories or 0.5 ounces and Mexican food by 133 calories, or 1.7 ounces," she said.
"There hasn't been enough focus on the sizes of portions, and that includes soft drinks and fruit drinks as well. Sometimes a conflict even exists between good nutrition and economics such as when you can get a significantly larger-size portion of French fries or soft drink for a very small extra cost."
When combined with less physical activity than in decades past, greater energy consumption significantly raises the risk of heart disease, stroke, hypertension, diabetes and other health threats, Popkin said. Related recent UNC findings were that all age groups ate more restaurant food -- including fast food -- than a generation ago.
"Dietary patterns are rapidly shifting in the United States, and these changes are important contributors to the growing epidemic of obesity and diabetes facing Americans," he said. "Clearly the problem is that Americans are eating too much food. The shifts in where we are eating, as well as the types of food and how much, are critical."
UNC researchers also earlier found large increases in snack eating, Nielsen said. In 1977, for example, snacks produced 11.3 percent of the average American's energy intake, while by 1996 that figure had climbed to 17.7 percent, which is more than a 50 percent increase.
"Although the elderly still snack the least, with 14 percent of their energy coming from snacks, they have had the largest jump in snacking, up from 7.7 percent in 1977, which is almost double," she said. "Among people under age 39, pizza and salty snack consumption rose as much as 143 percent."
The U.S. Department of Agriculture supported the surveys, which involved interviewing Americans about what and where they and their children had eaten over the previous few days and where the food they ate came, from such as stores and vending machines.
By DAVID WILLIAMSON
UNC News Services
Note: Nielsen can be reached at (919) 966-1734 or samara@unc.edu. Popkin's number is (919) 966-1732, and his email is popkin@unc.edu. He is currently out of the country.
News Services Contact: David Williamson, (919) 962-8596
School of Public Health Contact: Lisa Katz, (919) 966-7467
Journal
JAMA