Some restaurants voluntarily display the information, Lee-Kwan said, and some jurisdictions -- most notably New York City -- have passed local laws requiring menu labeling.
"Those local requirements could actually increase the menu labeling use in some states," Lee-Kwan said. "If it's not available, you can't use it."
Prior research has shown that many diners underestimate the caloric count of meals when they eat out, the report noted. It's believed that calorie labeling can help people who want to lose weight to order less fattening dishes.
Lee-Kwan and Mills said they're concerned that so many people -- 4 out of 10 in this survey -- still don't use the calorie information to help guide their meal choices.
Although the CDC study didn't address the point, prior research has shown that people who already eat right are more apt to use menu labeling, Mills said.
"I was not surprised that the data is not being universally used," she said. "Those who basically had healthy diets in the past were typically ones who used the nutrition information." This could blunt the impact that menu labeling could have on the obesity epidemic.
More than one-third of American adults is obese, the CDC says.
Marketing and communication strategies that draw attention to the menu labels or highlight particularly healthful options could attract more attention from people who usually ignore nutrition facts, the CDC report said.
"The implication is out there that if the nutrition information is posted and some groups are downright missing it or not using it, there's got to be some way to appeal to their interest and attention," Mills said.