“Finish what’s on your plate!” Thus has a multitude of well-intentioned moms exhorted millions of children, in an attempt to ensure good nutrition.

Unfortunately, dieticians now find, too many grownups still feel compelled to empty their plates–even when those plates contain substantially more calories than our bodies need. Add to that the fact that modern fast-cooked meals both at home and at restaurants carry more calories per recipe than a generation ago. What’s more, a new study finds, except for pizza, food portions have undergone substantial inflation over the past 2 decades.

Samara J. Nielsen and Barry M. Popkin of the University of North Carolina (UNC) analyzed a succession of government surveys on the eating habits of some 60,000 people. The two nutrition researchers now report in the Journal of the American Medical Association that a day’s worth of meals back in the 1970s typically provided 1,590 calories, and snacks about 200 calories more. By the mid-1990s, meals were delivering 1,635 calories; with snacks, the daily tally came to some 1,985 calories, or nearly 11 percent more than a generation earlier.

At least part of this increase appears to stem from the so-called supersizing of portions of many popularly consumed foods, wherever they’re served. For instance, the UNC researchers find that the typical hamburger grew from 5.7 ounces in the 1970s to an average of 7 ounces–97 calories more–by the mid-1990s. A serving of french fries increased from 3.1 to 3.6 ounces, adding 68 calories. And a typical serving of soft drink climbed 6.8 fluid ounces, or about 50 calories, to 19.9 ounces.

In terms of mealtime venues, Nielsen and Popkin report that fast-food restaurants serve the largest food portions; full-service restaurants, the smallest.

“The most surprising result is the large portion-size increases for food consumed at home–a shift that indicates marked changes in eating behavior in general,” say the researchers. In fact, for some foods, such as french fries, burgers, and Mexican foods, people reported eating the biggest portions at home, not at restaurants. For instance, the UNC analysis found that the average home-cooked hamburger now weighs in at about 8 ounces, versus perhaps 5.5 ounces in full-service restaurants and a little over 7 ounces at fast-food outlets.

The UNC scientists say their findings point to one factor contributing to the nation’s epidemic of obesity. Today, more than 64 percent of U.S. adults and at least 15 percent of adolescents are overweight, according to analyses published last year by Katherine M. Flegal and her colleagues at the National Center for Health Statistics in Hyattsville, Md.

Every extra 10 calories consumed per day–and not burned up in exercise or work–ends up as another pound of flesh or fat by the end of a year, Nielsen and Popkin note. So, if people are eating more today, they must become more active–or risk plumping up.

Ironically, Popkin notes, there has been a continuing cultural shift in the United States away from strenuous activities to sedentary ones. For instance, manual-labor jobs such as bricklaying and landscaping have given way to driving forklifts and lawn tractors. Similarly, hiking and biking might be replaced by moviegoing or cruising around in a car. Indeed, because of laborsaving appliances, even household chores burn fewer calories than they did 20 years ago.

With the trend away from physical activity unlikely to change soon, people must look to curb their calories. And the best way to eat less, the UNC researchers argue, is to cut food portions. However, with the growing trend to eat more often at restaurants (Home Cooking on the Wane), people are turning over the decision about portion sizes to someone else. This makes it essential for everyone to tune out that little voice in his or her head that still insists, “Finish what’s on your plate!”

Next week: A new tip for coping with dietary inflation: Close your eyes.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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