Restaurants are offering smaller, cheaper portions, but that doesn't mean dainty dining. Instead, people are using smaller dishes as an excuse to add to their orders, spending — and probably eating — just as much as before.

T.G.I. Friday's, Quiznos, Au Bon Pain and other "fast-casual" restaurants have introduced smaller, cheaper alternatives to supersize portions. The twist: Diners who order the petite portions are also likely to indulge in an appetizer or dessert.

An October article in The Journal of Consumer Research summarized three studies showing that low-calorie counts and health claims at fast-food restaurants have "a halo effect" that causes diners to underestimate the calories in main dishes and choose higher-calorie side dishes, drinks or desserts.

"These studies help explain why the success of fast-food restaurants serving lower-calorie foods has not led to the expected reduction in total calorie intake and obesity rates," wrote the authors, Pierre Chandon of France's INSEAD Business School and Brian Wansink at Cornell University.

Call it the room-for-dessert factor.

Friday's introduced its "Right Portion, Right Price" entrees last year after its research found that half of Americans wanted smaller portions.

The dishes, which are roughly one-third smaller and one-third cheaper than full-size entrees, have grown to 15 percent of total orders since they were introduced.

At the same time, diners' total checks stayed about the same, according to the company.

"The people who are eating this are not people who go out, and go home and feel like they want to take a nap or throw up. They want to split a dessert," said Richard Snead, president and CEO of privately-held Carlson Restaurants Worldwide, Friday's parent company.

The same thing seems to be happening at Quiznos, which has sold 5 million of its $2 mini "Sammies" sandwiches since their November introduction. The 200- and 300-calorie Sammies are now 16 percent of sales.

"We sensed a bit of a backlash on the full plate-ization of America," said Steve Provost, Quiznos chief marketing officer. "We think it's a great response to both the tug of the tight economy and the tight waistline."

But most sales come from people who buy two Sammies, as well as chips or a drink, he said.

"People in focus groups tell us they want control, they want to eat lighter," Provost said. "The fact that they are buying more than one and are buying a chip or a drink with us shows us they are choosing to fill up their plate again."

Bakery-cafe chain Au Bon Pain Corp. launched a "portions" line in November, with 200-calorie portions of 14 dishes, the most popular of which is a chickpea salad. Vegetarian portions are $2.99 and meat portions are $3.49.

The portions line is less than 3 percent of sales, with most customers buying them as "an add-on" to a soup or sandwich, said spokesman Ed Frechette.

"The average check has, at a minimum, held," Frechette said. "In many places, it's gone up."