December 4, 2014 5:54 AM EST

If you’re still blissfully unaware of how many calories are in your movie-theater popcorn, amusement-park funnel cake and frozen margarita, savor it–because you won’t be able to escape the truth a year from now. That’s when new rules from the Food and Drug Administration kick in requiring chain eateries to post calorie counts for all items on the menu–including drinks. The FDA hopes awareness about which foods are more caloric than others will prompt healthier choices and help stem the obesity epidemic. And considering that 25% of the people in one recent study underestimated the number of calories in the fast food they’d eaten by at least 500, those in-your-face counts could actually help.

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WHERE WILL THE NEW CALORIE TALLIES TURN UP?

At any chain that sells food and has 20 or more locations, including convenience stores, coffee shops, gas stations, pizza parlors, movie theaters, amusement parks and supermarkets with prepared-food sections. Your 3 p.m. snack is about to get hit with labels too. Though companies have two years to comply, anything in a vending machine will also come with calorie counts.

BUT DO CALORIE COUNTS REALLY AFFECT BUYER BEHAVIOR?

Research findings are mixed. Some studies suggest calorie counts nudge us toward lighter options, while others show they don’t make a big difference. One study found that posting calories influences customers in taco and coffee chains but not burger and sandwich shops. More research is needed, but one thing is clear: we are terrible at judging how much we eat. Public-health leaders are banking on the idea that raising awareness will help Americans adopt healthier diets.

300,000

Number of shops that will be required to show calorie counts after the rule takes effect

32%

Percentage of their daily calories Americans eat outside the home

ARE CALORIES THE MOST IMPORTANT THING IN MAKING A HEALTHY CHOICE?

It depends, since calories aren’t created equal, says Katherine Zeratsky, a registered dietitian at the Mayo Clinic. Whether foods are nutrient-dense is also important. A candy bar may pack the same number of calories as Greek yogurt with nuts, but your body will make use of and store the energy from them very differently. “Focus on eating the right things first, and then fit them into your daily calorie allotment,” says Kristin Kirkpatrick, a dietitian at the Cleveland Clinic’s Wellness Institute.

This appears in the December 15, 2014 issue of TIME.

Write to Mandy Oaklander at mandy.oaklander@time.com.

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