Today, you can buy one containing as many as eight ounces.
In 1955, a McDonald's hamburger came in one size -- with 1.5 ounces of meat. Today, a "super-sized" burger can have as much as eight ounces of beef. The portion of fries that come with it, 2.3 ounces in 1955, can be as big as 7.1 ounces. And the 7-ounce regular soda of 1955 is dwarfed by today's 42-ounce super-sized serving.
And so it goes in category after category of prepared foods, says a report in the February issue of the Journal of the American Dietetic Society. Increasingly, Americans are being tempted to buy more food than is good for them, the report says.
It's a temptation that is a major contributor to an epidemic that sees more than 60 percent of the nation as overweight or obese.
Why the portion distortion?
"Money," says Marion Nestle, chairwoman of the department of nutrition and food studies at New York University and author of the report.
"It doesn't cost the manufacturer very much to make larger portion sizes, since the biggest factor in cost is labor," Nestle says. "The food itself is relatively cheap."
Nestle has elaborated on the theme in a recently published book, "Food Politics: How the Food Industry Influences Nutrition and Health." Food companies are "very competitive for the consumer dollar," she says, and increasing portion size is an easy way to attract more customers.
Consumers love getting more of each portion because "there isn't anybody telling them not to do that," and they like getting what looks like a bargain, Nestle says.
If you look hard at the label that the U.S. Food and Drug Administration (FDA) requires on a package of prepared food, you'll see a recommended portion size, and the calories it contains. However, the FDA rules say a food portion weighing up to twice the standard serving can be labeled "one portion per serving."
Consumers can also be confused by discrepancies between what the FDA and the Department of Agriculture (USDA) define as a serving, Nestle says. For example, the USDA standard for a serving of cooked pasta is half a cup, but the FDA standard is a full cup.
In addition, many Americans believe that the kind of food they eat --staying away from fatty food to prevent heart disease, for example -- is more important than how much food they eat, Nestle says.
The root of the problem is that the United States is awash in inexpensive food, with subsidized farmers encouraged to overproduce, Nestle says. Effective lobbying keeps subsidies flowing to food producers who can sell their produce cheap, she contends.
There are several strategies, most involving discipline, that consumers can follow to avoid the large-portion trap, says Wahida Karmally, an associate research scientist at Columbia University and a spokeswoman for the American Dietetic Association.
One is to stick to the small portions of any offering. "When I counsel my patients, I tell them, 'If you enjoy the taste of food, whether you eat a lot or a little, it tastes the same,'" she says.
If tempted to order a larger portion, share it with a friend, Karmally says. "And if you are hungry, you can eat fruit or vegetables," she says.
Keith Ayoob, an associate professor of pediatrics at Albert Einstein School of Medicine in the Bronx, N.Y., says, "In general, people are not getting enough of fruits and vegetables. If you have them on your plate, there is a lot less room for things with higher calorie content."
However, "overeating is a condition of excess, and excess is becoming more common," Ayoob says. "Even if you eat good, healthy food, too much of anything is too much."
Several calls to McDonald's officials for comment were not returned.
You can learn about the problems caused by overeating from the National Institute of Diabetes and Digestive and Kidney Diseases. For more on the U.S. obesity epidemic, visit the U.S. Centers for Disease Control and Prevention.