A large Skyline Chili 3-way contains 1,100 calories. (Skyline Chili/Twitter)

Mark Keilholz starts the signature dish with a steaming heap of spaghetti. He soaks it in chili. Tops it with shredded cheddar cheese.

“Most of my customers never look at a menu,” says Keilholz, 65, owner of a Skyline Chili franchise in Dayton, Ohio. “They’ve been coming in for years. They know exactly what they want.”

That’s why no menu board hangs in his suburban store, which has served chili bowls and coney dogs for three decades. New customers, which are a rarity, can reference pamphlets.

Those pamphlets — and Skyline Chili’s protocol — will soon get a major edit. The Food and Drug Administration on Tuesday approved new rules that will mandate calorie counts and force American diners to acknowledge the zipper-straining reality of, say, the Cheesecake Factory’s Bruléd French Toast (2,780 calories). Or a large popcorn at an AMC movie theater (1,030 calories, without butter). Or a large 3-way at Skyline, which Keilholz calls a cult classic in the Midwest (1,100 calories).

Four-digit calorie counts won’t deter his customers, he said. Little can: “Neither Rain nor sleet nor 40 MPH winds will keep Skyline customers from getting Cheese Coneys,” the store’s Facebook page proclaimed Monday.

“They come for the atmosphere,” Keilholz said. “They come because when you grow up around here, sooner or later your parents will drag you to Skyline and you learn at a young age to just love it.”

The new FDA rules will cost the company time and resources, he said. And for what? Health-conscious customers can find Skyline’s calorie counts online.  “We’re known for our chili — not for our salads. We’re successful in the niche that we fill. If you try to be everything to everybody, you sacrifice your product. Your quality.”

Diners ripped from ignorant bliss can thank Obamacare. The rules are part of the Affordable Care Act’s push to curb obesity in America, where a third of calories are devoured outside the home. This country of brunchers and craft beer chuggers and orderers of Taco Bell’s Fourth Meal has one of the highest obesity rates in the world, according to the OECD.

Labeled menus will help consumers make more informed food decisions, FDA Commissioner Margaret A. Hamburg told reporters this week — and by extension boost public health. Obesity increases the risk of cancer, diabetes, stroke and heart attacks, the CDC warns.

The FDA’s idea: Knowledge is health power. A survey published in the American Journal of Public Health showed Americans underestimate the caloric content of restaurant foods by an average of 600 calories, Wonkblog’s Jason Millman noted. That’s a meal’s worth of misjudgment.

Starting next year, detailed nutritional information will appear at coffee shops, pizza joints, movies theaters — any food-seller with more than 20 locations. Skyline has more than 130 stores.

The FDA first issued the proposals in 2011. Debate about what food should be subject to the rules — and backlash from pizza places, theater chains and consumer advocates — stalled progress. Some business owners worried labeling menus would be a time-consuming process that could ultimately drive up costs for customers.

“It was much more complicated than we originally thought it would be,” Hamburg told the Post.

Four years ago, as the FDA polished its sweeping requirements, Stanford researchers studied the impact of mandatory calorie posting on purchase decisions at Starbucks stores across New York City. Food purchases slightly dipped, they found, but business overall didn’t suffer.

Drink orders remained consistent. The staple lattes still reigned. The mocha sauce kept flowing.

Nothing substantial will change at Skyline, Keilholz predicts. He watched it grow from one Cincinnati store to dozens across the Midwest and Florida. The same formula has worked, he said, since 1945.

His first job in high school was serving chili at the original store, where Keilholz met his future wife, Cynthia, the granddaughter of Skyline’s founder. Their grown son Chris will eventually take over the Dayton franchise.

Keilholz sees no need for calorie labels. He knows exactly what goes into each greasy, cheesy dish.“I still eat the chili every day,” he says. “I’m hanging in there. The doctor says I’m okay.”

Calories, he suspects, will be the least-read items on the little-read menus.