It’s finally happening. After nearly a decade of delays, the Food and Drug Administration is expected to implement an Obama-era policy that will require restaurants and other food outlets with 20 or more locations to post calorie counts beginning May 2018.

Any big chain — from grocery stores to movie theaters, amusement parks to vending machines to restaurants — will have to show how many calories come with their sandwiches, popcorn, cocktails, and french fries. Up front. Right on the menus.

In some eateries, menu labeling is already happening. Several major chains started to move in this direction because the FDA was expected to finalize this regulation years ago. It’s why you can see that your grande latte at Starbucks has 190 calories, your turkey, apple, and cheddar sandwich at Panera has 710 calories, and your McDonald’s Big Mac packs 530 calories, for example.

But we’ll soon be saturated in calorie data — everywhere. These changes aren’t expected to cause Americans to suddenly clean up their diets, but they could have profound indirect effects on how we think about food and nutrition, what we choose from the menu, and ultimately what restaurants serve.

We now get most of our calories from eating out — but it’s been hard to know what we are eating. That will soon change.

Americans do a lot of their eating outside of the home these days. More than half of the money spent on food goes to restaurants and convenient on-the-go meals — not to groceries cooked at home.

Make no mistake: When we dine out, we eat more. People typically consume 20 to 40 percent more calories in restaurants compared with what they’d eat at home. We do that because it’s easy to do in restaurants. As Tuft University researchers found, in the Journal of the Academy of Nutrition and Dietetics, restaurant dishes at non-chain establishments across the country typically contained 1,200 calories — about half of the 2,000 or 2,500 calories recommended for moderately active women and men in an entire day. For these reasons, the American propensity to dine out has been linked with the obesity epidemic.

For a long time, consumers were left to operate blindly when it came to knowing how many calories they were consuming. Unlike the nutrition facts panels that come with preprepared foods we eat at home, there was no such transparency around restaurant food.

Then along came the Affordable Care Act in 2010. Buried among its many provisions were rules requiring "retail food establishments" with 20 or more locations to post "on the menu listing the item for sale, the number of calories contained in the standard menu item,” as Vox’s Sarah Kliff reported. Another section in the law mandated vending machines "provide a sign in close proximity to each article of food or the selection button that includes a clear and conspicuous statement disclosing the number of calories contained in the article."

The hope was that these regulations would help people calculate how many calories they were eating, and maybe make an impact on obesity.

The Food and Drug Administration, which regulates the food industry, was in charge of finalizing and implementing menu labeling. But the Obamacare mandates, even under President Barack Obama, were beset by delays because of intense lobbying from various factions of the food industry.

American pizza makers have pushed for, among other things, only posting calories for serving sizes they determine, instead of the actual serving sizes people are going to eat. Convenience stores and supermarkets argued menu labeling, while appropriate for restaurants, would be too expensive and burdensome for them. Movie theaters for their part tried to keep their 1,000-calorie popcorns out of the calorie postings.

On Thursday, the FDA finally released draft guidance about how the industry will have to comply with the menu labeling rule by May 2018. Health advocates said they were pleased to see the rule was left mostly intact.

“I was relieved to see details of the guidance for FDA,” said Margo Wootan, director of nutrition policy at the Center for Science in the Public Interest. “It didn’t substantively change the way calories will be disclosed.”

This came as a surprise, because the Trump administration had pushed back the implementation of the rule just before it was supposed to go into effect last May.

CSPI has sued the FDA over menu labeling, arguing that its delays were not legal. The nonprofit put the lawsuit on hold in September because the administration reassured the group that they planned to move forward with the May 2018 deadline. “So our agreement with the agency — that has been signed off on by a judge — is also reassuring,” said Wootan.

But the fact that the guidance was released far ahead of the rule’s implementation date suggests businesses will have plenty of time to comply (and little space to argue that they didn’t have enough time to meet the requirements of the regulation).

FDA Commissioner Scott Gottlieb also pledged his personal interest in getting this job done, as Politico’s Helena Bottemiller Evich reported, and announced his agency’s commitment to nutrition.

“As someone who enjoys eating out with my family and picking up the occasional take-out meal, I — like many Americans — want to know what’s in the food I eat,” Gottlieb said in a statement. “FDA takes seriously the authority Congress granted to us in overseeing federal food labeling standards, including our mandate to make calorie information available on menus.”

“Now there’s a different administration in place that didn’t drive calorie labeling from the beginning saying they’re going to implement it in 2018,” said Jason Block, a physician and researcher at Harvard Medical School who has been studying calorie labeling. “I think most of us are fairly confident that it’s going to happen.”

The law could have a far-reaching impact, and not just on the food choices individuals make

The evidence we have on calorie labeling’s impact on health is pretty mixed. The studies and meta-analyses either suggest that calorie labeling has had little impact on people's food choices or that the available studies are too poorly designed to really tell. Researchers have also found that people who are already calorie-conscious do pay attention to labels, but those who aren't don't. In other words, just having that information displayed doesn't change people's behaviors.

So health wonks don’t expect people will immediately start making healthier food choices when menu labels come out.

But calorie labeling is expected to do two other things: push food producers to reformulate products so that they aren’t so hideously high in calories, and change consumer attitudes about nutrition.

Researchers have found that after a menu labeling was implemented in Seattle in 2009, food purveyors tweaked their recipes and lowered calories, for example.

Menu labeling also causes people to talk about calories in foods — raising awareness about nutrition, as this Health Affairs study pointed out:

For example, a recent article in the New York Times showed that the typical order at Chipotle contains about 1,070 calories—twice as many calories as a Big Mac and “more than half of the calories that most adults are supposed to eat in an entire day.”

According to Harvard’s Block, “The story about tobacco policies and how smoking patterns have changed is as much a story about changing social norms as it is about specific policies. This widespread implementation of a public education campaign like calorie labeling should change the public’s consciousness about calories.”

We know from the soda tax debate that it’s been hard to disentangle what impact the taxes are having from the awareness the tax debate raised about the health impact of soda. The same may be true about calorie labeling — and perhaps that means that all the discussion about this Obama-era mandate and the years of news articles about delays in the press means it’s already having an effect.