The calorie-posting mandate, signed into law by President Barack Obama as part of the health care overhaul, assumes diners will feel the culinary equivalent of sticker shock when confronted with calorie counts for greasy, sugary and fatty foods.
Anti-obesity advocates also hope that forcing restaurants to reveal calorie counts will coax the chains to offer healthier options.
Early studies do show some modest changes in consumer behavior in New York City, which enacted its pioneering calorie-posting law in 2008. But whether the measure also is pushing healthier items onto menus is less clear.
While chain restaurants have introduced scores of healthier menu items in recent years, most say the changes are coincidental to calorie-posting laws, an effort to keep pace with consumer demand for healthier items.
Not so for Le Pain Quotidien, a bakery and restaurant chain with more than a dozen locations in New York City. Olivier Arizzi, brand marketing manager, said the law definitely prompted changes, including making some pastries smaller to cut calories.
"It forced us to innovate," Arizzi said. "We would have had certain pastries that were very popular before, not being popular anymore because the calorie count would be so high."
Arizzi said they did not need to make changes to their sandwiches and salads.
But other major restaurant chains contacted by The Associated Press cited other reasons for menu tweaks, chief among them the need to satisfy health-conscious customers.
"You hope the calorie posting is going to put pressure on the chain restaurants - because they have to post those calories - to reformulate and make small changes in what they offer," said Cathy Nonas, who directs the New York City health department's physical activity and nutrition programs. "And indeed, we're seeing that. Obviously not with everything, but there are changes in almost every restaurant."
Nonas is looking at menu offerings by chain restaurants before and after the city law took effect. Among the changes she noticed since 2007: Dunkin' Donuts launched its lower-calorie DDSmart options, KFC began selling grilled chicken, Starbucks switched to lower-fat milk for espresso-based drinks and McDonald's cut its serving size for large french fries by 0.6 ounces.
Nonas does not claim a causal link between the city law and healthier food items, she's just happy they're being offered.
The federal legislation will require chain restaurants with 20 or more locations to include calorie counts on menus, menu boards and drive-thrus. The Food and Drug Administration will have a year to write the new rules, which will supersede local laws in places like New York, Philadelphia and California.
Health policy analysts still are measuring the affect of the local laws, focusing mostly on how they influence consumer behavior. Researchers at the Stanford Graduate School of Business found that calorie postings in New York City Starbucks led to a 6 percent reduction in calories per transaction.
Brian Elbel of New York University's School of Medicine found about one in four New York City customers who noticed the calorie labels said it influenced their choices, though his study didn't detect people actually purchasing fewer calories.
People eating fast-food lunches Tuesday at chain shops in Albany, N.Y., seemed indifferent to the calorie numbers now posted on menu boards.
"I noticed it, but I ignored it," said Stacy Rijssenbeek, who shared a 12-inch spicy Italian Subway sub with her mother. "It's all a bit overwhelming. I'll have to get used to it."
Over at McDonald's, Sean Ryan said he didn't even notice the calorie numbers as he ate his Chicken McNuggets.
"I exercise," he said. "It doesn't really bother me. I only eat at McDonald's when I'm too lazy to pack a lunch."
Research into restaurant reactions to posting laws is rare, with studies in New York City and Seattle still under way. University of Washington epidemiologist Barbara Breummer, who is conducting the Seattle research, cautioned that it can take time for restaurants, particularly larger chains, to develop and introduce new items. The law for Seattle and surrounding King County was enacted in January 2009.
Many public health researchers believe labeling laws will end up having at least some affect on fast-food formulations. One researcher noted that packaged food manufacturers reduced the amount of trans-fats in their products after being required to list the levels.
But Elbel noted that restaurants change their menus all the time, and it can be hard to tease out the reasons for changes.
"It's maybe a fair bet to say that labeling likely has something to do with this," Elbel said, "but we're not at a point scientifically where we can say that with any kind of clarity right now."