TOLEDO, Ohio (CBS) — President Barack Obama was born in Hawaii and didn’t move to Chicago until he was 23 years old, but nevertheless, he proved Friday that he is, in fact, a true Chicagoan.

The proof? He confirmed that he is against putting ketchup on hot dogs.

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President Obama was in Toledo, Ohio, Friday, and stopped for lunch with that city’s mayor, Michael Bell. Obama’s meal of choice a chili dog at Rudy’s Hot Dog in Toledo, but the subject of ketchup on came up during lunch.

“You shouldn’t put ketchup on your hot dog,” the president said straightforwardly.

It may be acceptable in some parts of the country, but as any Chicagoan knows, there are fewer infractions more serious in these parts than slathering a hot dog with ketchup.

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The local commandment is so legendary that a definitive book about the world of hot dogs, authored by no lesser authority than Vienna Beef vice president Bob Schwartz, is titled, Never Put Ketchup on a Hot Dog.

In a “Straight Dope” column published back in 1991, the renowned Cecil Adams said there is actually a legitimate gustatory reason for keeping ketchup off your hot dog.

“Ketchup smothers the flavor of the hot dog because ketchup makers add sugar to their products,” he wrote. “That takes the edge off the highly acidic tomatoes, but it takes the edge off everything else, too.”

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If you order a hot dog in Chicago, the proper condiments are mustard, sweet pickle relish, chopped onions, sliced tomatoes, a kosher pickle spear, sport peppers, and celery salt.