Restaurant menus that include calorie information do seem to encourage diners to exercise some restraint, a new US study suggests.

What's more, researchers found, menus that give added information – namely, the number of calories the average adult should get in a day – could prove even more effective at curbing appetites.

The findings, reported in the American Journal of Public Health, give some weight to the growing movement to require restaurant chains to place calorie information on their menus and menu boards.

In 2008, New York City became the first US city to mandate such changes at fast-food and coffee chains. That law became a model for California and other states and cities that have since implemented or are considering similar measures.

And soon the federal government may be stepping in; provisions for menu labeling are part of the healthcare reform legislation.

The intention is to help combat the nation's obesity problem by raising consumer awareness of just how many calories lurk in their burgers, sandwiches, chips and desserts.

But questions have been raised about the effectiveness of menu labelling.

In October, an independent study of New York's law concluded that menu labelling had done nothing to change consumer habits in the city's low-income neighbourhoods.

Shortly thereafter, the city's health department released preliminary data from a larger study suggesting that New Yorkers had, in fact, started buying fewer calories at nine of 13 fast-food and coffee chains included in the research.

For the current study, Yale University researchers tested the effects of menus that provide not only calorie content, but also a line stating that the average adult should get about 2000 calories a day.

The researchers randomly assigned 303 adults to order from one of three menus: one with no calorie labelling; one with calorie information; and one with calorie content, plus a label with the 2000-calorie recommendation.

Overall, the study found, diners in the two calorie-label groups ate 14% fewer calories at the meal than those who had ordered from the label-free menus.

And when study participants later reported on their food intake for the remainder of the day, the researchers found that those who had seen the 2000-calorie recommendation downed fewer calories – an average of 250 fewer than those in the other two groups.

The setting was experimental, and not "real world," but that allowed the researchers to show cause-and-effect, noted Christina Roberto, a doctoral candidate at Yale who led the study.

"We can say that is the menu labelling having the effects" on calorie intake, she told Reuters Health.

Moreover, Ms Roberto said, the findings highlight the potential impact of a simple line stating the number of calories a person should get each day.

"That turned out to be really important," she said, noting that the information helped people put their single meal in the context of a whole day.

"By putting that 'anchor' in, you can maximise the effectiveness of menu labelling."