Nutritional information is coming to U.S. vending machines, but research shows it may not work as intended.

If you wanted to know how many calories are in a 1.5 oz bag of Harvest Cheddar Sun Chips sold in a vending machine, you used to have to buy them and then check the nutrition label on the back. (It’s 210 calories, in case you’re wondering.)

Now, more than five million vending machines in the U.S. will have to display nutritional information front and center so consumers know before they plunk down their coins. The change, which began Jan. 1, is one provision of the Patient Protection and Affordable Care Act, better known as Obamacare.

The goal is to help Americans make better nutritional choices and to reverse an alarming trend: nearly 70 percent of the nation’s adults are considered overweight or obese. Cities across the U.S., including New York, San Francisco, and Philadelphia, have already implemented policies mandating that chain stores post nutritional information about their ready-to-eat food in plain view.

When Obamacare was passed in 2010, chain restaurants with 20 or more locations were initially required to provide nutritional information, but that particular national labeling requirement has been postponed. The provision was intended to help inform consumers that frequently eating meals outside the home is a risk factor for obesity. Foods prepared in restaurants are typically higher in calories, fat, sodium, and sugar.

Get Informed: Learn to Spot Restaurant Lies »

But, the effects of food labeling may not be as drastic as lawmakers intended. Research from Carnegie Mellon University (CMU) suggests that food labeling has little effect on consumer behavior.

During one study, CMU researchers surveyed the choices of 1,121 adults having lunch at two McDonald’s restaurants in New York City, where mandatory food labeling was implemented in 2008. They found little to no change in diner’s orders based on the newly posted nutritional information.

“Making the information available on menus may have other beneficial effects, such as motivating restaurants to change their formulations. But it may be unrealistic to expect many consumers to keep such close, numeric track of their food intake by using the labels directly,” lead author Julie Downs, an associate research professor of social and decision sciences in CMU’s Dietrich College of Humanities and Social Sciences, said in a statement.

A separate study published in the journal Obesity found similar results—displaying nutritional information at fast food restaurants in Philadelphia and Baltimore had no meaningful effect on people’s food choices.

While fast food restaurants may not be the best place to reach calorie-conscious consumers, new research from the U.S. Centers for Disease Control and Prevention (CDC) estimates that just over half of Americans do read food labels.

Learn How to Understand Nutrition Labels »

The CDC study, released Thursday, examined three states—Minnesota, Wisconsin, and Hawaii—that have added a specific question about labeling to their annual Behavioral Risk Factor Surveillance System telephone survey.

Minnesota, which is often named one of the country’s healthiest states, has an average self-reported obesity rate of 25.7 percent, according to the CDC. Wisconsin and Hawaii have rates of 29.7 and 23.6 percent, respectively.

Researchers found that those who said they read food labels were more likely to be female, to have a household income above $50,000, and to meet federal guidelines for regular aerobic exercise. A person’s body-mass index, or BMI, had no significant effect on their willingness to real nutrition labels.

Those who read nutrition labels also regularly consumed more fruits and less soda than those who did not take advantage of menu labeling.

“Menu labeling is intended to foster a nutritional and health behavior change; however, our study results show an association between menu-labeling usage and participation in healthy behaviors,” researchers concluded.

Results from other reports on the effects of food labeling have been mixed, mainly due to small sample sizes.

One study in the Journal of Nutrition Education and Behavior suggests that more efforts will be required to reach those in low-income areas, who are more likely to be obese and to suffer from other diet-related diseases.

That study included 37 parents responsible for purchasing food for their overweight children. Few recognized that their children had a weight problem, and those who looked at food labels were mostly concerned about additives, not calories.

Read More: How Food Labels Can Suck Us Into the Health “Halo” »