Calorie labeling on restaurant menus -- as required of many restaurants under the federal Patient Protection and Affordable Care Act of 2010 -- can only help people manage their weight if those listings are correct. Research published today in the Journal of the American Medical Association has concluded that, by and large, restaurants are providing fairly accurate information.

Led by researchers at Tufts University, the study compared the stated calorie content of 269 menu items from 42 restaurants with laboratory-measured counts for those foods. The study included foods from quick-serve and sit-down restaurants. While 40 percent (108 items) had calorie listings that were at least 10 calories per portion lower than their actual calorie content, even more -- 141, or 52 percent -- had calorie listings that were at least 10 calories per portion higher than their actual calorie count. Nineteen percent of the items contained more than 100 calories per portion more than represented by the restaurants.

All in all, quick-serve restaurants did a better job of providing accurate calorie information than sit-down restaurants. The study suggests that the difference may stem from the fact that quick-serve restaurants serve more pre-portioned foods, while sit-down restaurants size their portions themselves, leading to more variation in serving size.

It’s important to pin this down because Americans get about a third of their calories -- 35 percent, according to the study -- from foods bought from restaurants.

Of course, calorie listings, accurate or otherwise, can only work if people pay attention to them. Whether that's going to pan out remains to be seen.