BUENOS AIRES — A thick slab of grass-fed sirloin dripping in its own juices: so many Argentines consider such a feast a birthright to be enjoyed regularly that one president in the 1990s quipped to an American magazine, “Tell your readers, ‘Don’t come to my country if they’re vegetarian.’ ”

But tastes change, even here.

Beef consumption in this red-meat colossus has decreased so much over the decades that the nation recently fell from its perch as the world’s top per capita consumer of beef, a title Argentine ranchers are fighting to regain from their tiny neighbor, Uruguay. In another jolt, a study warned that pizzerias could soon outnumber steakhouses in this city.

As if that were not enough to rattle the national psyche, Argentina slipped into 11th place, behind countries like New Zealand and Mexico, in the global ranking of beef exporters this year, prompting solemn reactions like one in a major newspaper that declared it “the end of a reign.”

“We live, at this moment, immersed in shame,” the writer Diego Vecino said in a recent 4,000-plus-word magazine article that explored declining beef consumption. “In the last few years, our Argentine national identity has been roughed up as never before,” he lamented, in a slightly tongue-in-cheek fashion. “The ritual of the barbecue persists, but in many cases under the kitsch glow of a retro experience.”