Chicago ? Americans aren’t just supersizing their portions in fast-food restaurants, they’re doing it in their own kitchens.

In a new study, researchers looked at such foods as hamburgers, burritos, french fries, sodas, ice cream, pie, cookies and salty snacks and found that the portions got bigger between the 1970s and the 1990s, regardless of whether people ate in or out.

It is no surprise it happens at fast-food restaurants; it was McDonald’s that helped put the word “supersize” into the American lexicon.

But Margo Wootan of the Center for Science in the Public Interest said the practice has caused Americans to suffer portion distortion at home.

“We’re getting so used to these big portion sizes when we eat out that when we go home we forget what a normal portion is,” said Wootan, the center’s nutrition policy director.

Portions for all of the popular foods studied, except pizza, increased both inside and outside the home between 1977 and 1996. The study was conducted by researchers at the University of North Carolina at Chapel Hill and was published in today’s Journal of the American Medical Assn.

“An important point is not just what foods we’re eating, it’s the fact that we’re eating such large portions of these foods,” said researcher Samara Joy Nielsen.

The findings come at a time when Americans are getting fatter. A study by the Centers for Disease Control and Prevention found more than 44 million Americans were obese in 2001.

The University of North Carolina study looked at people’s portions at home, in fast-food joints and at other restaurants. It included a sample of 63,380 people over the age of 2.

Homemade burgers beefed up to 8.4 ounces in 1996 from 5.7 ounces in 1977, while fast-food hamburgers grew to 7.2 ounces from 6.1 ounces during the same period. At restaurants other than fast-food ones, hamburgers declined to 5 ounces in 1996 from 5.3 ounces in 1977, according to the study.

The U.S. Department of Agriculture counts two to three ounces of cooked lean meat as a serving.

Not surprisingly, the study found more calories went along with the extra food. A person who ate Mexican food in 1977 consumed an average of 408 calories in one sitting, compared with 541 calories in 1996.

The USDA suggests between 1,600 and 2,800 calories per day depending on a person’s age, gender and activity level.

Steven Anderson, the president and chief executive of the National Restaurant Assn., said, “You don’t have to go into a restaurant and eat everything the restaurant offers.”