Sacha Pfeiffer reports on WBUR that D’Angelo’s tuna sub or D’Angelo’s cheeseburger sub? Which one is the better choice if you’re watching your weight? Would you have guessed the cheeseburger sub has almost 200 fewer calories?

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State public health officials want to end those surprises by requiring chain restaurants to prominently display the calorie content of their food offerings on their menus or menu boards. The rule, expected to be approved Wednesday, is meant to fight obesity.

At Danehy Park in Cambridge, about a dozen women in tennis shoes and T-shirts meet for Ultimate Bootcamp. It’s an outdoor fitness class led by personal trainer Judith Forman. She makes the group run, stretch, do jumping jacks and do other exercises to help them get in shape.

“Tight abs,” she called to the class. “Go. One, two, three, four…”

Besides counting lunges, kicks and squats, Forman also wants these women to count calories. But she worries that’s hard to do for on-the-go people who frequently eat take-out.

“There’s no way of knowing when you walk into a restaurant what is in your food — if butter is used, fat, oil, extra mayonnaise,” Forman said. “It’s a guessing game.”

The state’s public health department wants to eliminate that guesswork. Because even some health-conscious people who think they have a good idea of calorie content can be shocked by the actual number.

State Health Commissioner John Auerbach includes himself among those who’ve gotten a startling dose of reality.

“I would go every morning to Starbucks and have a bran muffin, thinking that was the healthy item,” Auerbach said. “Sounds healthy, right? I went to New York and I saw it was 450 calories, and I’ve never ordered one again.”

Auerbach saw that number because last year New York City began requiring chain restaurants to list calories next to a food’s price. Besides making customers think twice about ordering certain items, the rule prompted some chains to start using lower-calorie ingredients.

Auerbach says one restaurant made a small change that resulted in a big health improvement.

“They decided to make the tuna fish sandwiches with low-fat mayonnaise and it reduced the amount of calories in the sandwiches by hundreds. And customers didn’t notice. Nobody said, ‘I used to like it, now I don’t.’ So we’re hoping and, frankly, expecting that we’ll see more and more things like that.”

Massachusetts has modeled its proposed regulation after New York’s, which has been upheld in federal court. Chain restaurants are being targeted because their menus are similar nationwide and because they often attract lower-income customers already carrying extra weight.

If the rule passes, it will go into effect late next year and apply to restaurants with 20 or more outlets in the U.S. Nearly 3,000 restaurants in Massachusetts would be affected.

At one Dunkin’ Donuts in Worcester, Wanda Cormier orders an iced coffee, no sugar. She welcomes the idea of being able to see calorie content right at the counter.

“Who isn’t counting calories when the summer’s right around the corner?” she asked. “Bathing suit weather is coming! I won’t get the donut. I’ll get the wheat bagel or something.”

But it turns out some bagels contain more calories than donuts. That’s why health officials want calorie content posted front and center: so customers can make more educated decisions about what they eat.

Some customers here say calorie listings wouldn’t affect what they order, and a woman named Violet says the rule would create unnecessary work for restaurants.

“As far as I’m concerned, people ought to take responsibility for their own actions,” she said. “Forget it. I don’t approve of that.”

As she waits for her ham and cheese flatbread, another customer, Joan, asks why restaurants don’t provide as much nutritional information as grocery stores already do.

“What do they have to hide, except than how many calories you’re getting. It’s probably more than you think.”

Rob Branca says Dunkin’ Donuts isn’t trying to hide anything. He and his family own this Worcester franchise, as well as about two dozen other Dunkin’ Donuts stores in Massachusetts. He says the chain already puts calorie information on its Web site, and posting those numbers in each store would be a burden.

“We already have the information,” Branca said. “Dunkin’ Donuts has spent the money to get the information. The problem is we would have to design, manufacture, distribute and then install new menu boards.”

Branca says some small stores may not have room to list calories and he warns that the added expense could put some of them out of business. He also thinks there should be one federal rule, not a patchwork of state regulations.

But health officials say New York’s regulation went into effect smoothly, even though restaurant owners there had similar concerns. And with half of Massachusetts adults now overweight or obese, state officials say they want to do whatever they can — as quickly as possible.