Brian Elbel, an assistant professor of population health and health policy at New York University’s School of Medicine, studied consumer behavior before and after the city required chain restaurants to post calorie counts in 2008.

He found that 54 percent of respondents in New York City said they noticed the calorie labeling. Of those, less than a quarter said they ate fewer calories as a result.

BUT their behavior did not, in fact, change. When Dr. Elbel analyzed consumers’ receipts, he found that there was no difference in calories consumed, whether people said they responded to the calorie counts or not. Consumers may be engaging in what behavioral economists call hyperbolic discounting, he said. “It’s just easier to imagine what this is going to feel like now, and harder to think through what it feels like later,” he said.

When New York City financed another study after the calorie labeling went into effect, over all, the study found no difference in calories consumed before and after the labeling requirement. But there were specific changes.

While just 15 percent of customers said they used the calorie information, those who did ate 106 fewer calories than those who didn’t. Some chains like McDonald’s and KFC saw significant reductions. But at Subway, which nutrition experts say has one of the healthier menus around, and where a higher-than-average percentage of customers said they read calorie information, the number of calories consumed actually increased, from 749 to 882. The researchers hypothesized this was because Subway was promoting $5 footlong subs at the time, and economic incentives trumped healthy intentions.

“What we’re learning from what’s happening in the industry is, consumers don’t see fast food as a place to eat healthy,” said Mr. Tristano, the food consultant. “It’s indulgence that’s important.”

Researchers are thinking of new ways to signal nutritional value: how much exercise it would take to burn off a menu item, symbols like traffic lights, or educational campaigns on understanding calories.