As an experiment, I picked up some signature dishes at popular New York spots. I got the works at Shake Shack. A New York strip steak with creamed spinach at Michael Jordan’s Steakhouse. From Ollie’s, the Chinese chain, cumin-flavored lamb (“I eat that and need to consume about a gallon of water afterward,” one foodie warned me). A slice of candy bar pie from Momofuku Milk Bar, because a sprinkle of salt gives desserts there an edge. House-made saffron pappardelle with braised rabbit at the Standard Grill, because it looked so luscious. The corned beef at Katz’s Delicatessen, because, well, how could you not?

At Two Boots, I could have ordered the vegetarian Earth Mother pizza, but I opted for the Dude, a Cajun bacon-cheeseburger pie. “I’ll have two Dudes,” I told the guy behind the counter. “We’re the only two dudes you need,” he said, gesturing to his friend at the register. That seemed pretty salty.

Instead of indulging, I put the dishes into Ziploc bags and sent them off to Certified Laboratories in Plainview, on Long Island, to be tested for sodium. Then I had to wait for the results.

When a chef cooks in what Mark Erickson, the dean of culinary education at the Culinary Institute of America, called a “fresh-prepared food environment,” salt is only one of the many tools — along with garlic or citrus or fresh herbs, say — she can use to build flavor. But if you’re stirring a huge vat of goo in an industrial food factory a mile below the earth’s surface, salt is one of the only tricks you have, so you have to use it a lot. As a result, sodium levels in a sit-down restaurant might be much lower than in fast food, even if the flavor is more intense.

Image CONSULTING A PROFESSIONAL Dan Silverman, head chef at the Standard Grill, talks to the City Critic about how salt is used at the restaurant. Credit... Joshua Bright for The New York Times

But at least in fast-food chains you can know what you’re getting: in New York, they are required to post nutritional information, which they more or less stick to. Better restaurants rely on the palate of not just the chef who creates the dish, but also the line cook who executes it. “When we say ‘season to taste,’” Mr. Erickson warned, “if you’ve been slaving in a hot kitchen your taste might be different from someone who’s been sitting at a desk in an air-conditioned office all day.”