A study of New York City’s pioneering law on posting calories in restaurant chains suggests that when it comes to deciding what to order, people’s stomachs are more powerful than their brains.

The study, by several professors at New York University and Yale, tracked customers at four fast-food chains  McDonald’s, Wendy’s, Burger King and Kentucky Fried Chicken  in poor neighborhoods of New York City where there are high rates of obesity.

It found that about half the customers noticed the calorie counts, which were prominently posted on menu boards. About 28 percent of those who noticed them said the information had influenced their ordering, and 9 out of 10 of those said they had made healthier choices as a result.

But when the researchers checked receipts afterward, they found that people had, in fact, ordered slightly more calories than the typical customer had before the labeling law went into effect, in July 2008.