On Thursday, Facebook announced plans to make similar changes to its News Feed around the world. The company said it was trying to increase “meaningful interaction” on its site by drawing attention to content from family and friends while de-emphasizing content from brands and publishers, including The New York Times.

The changes are being made as the company finds itself embroiled in a larger debate over its role in spreading fake news and misinformation aimed at influencing elections in the United States and other nations.

Facebook said these News Feed modifications were not identical to those introduced last fall in six countries through its Explore program, but both alterations favor posts from friends and family over professional news sites. And what happened in those countries illustrates the unintended consequences of such a change in an online service that now has a global reach of more than two billion people every month.

In Slovakia, where right-wing nationalists took nearly 10 percent of Parliament in 2016, publishers said the changes had actually helped promote fake news. With official news organizations forced to spend money to place themselves in the News Feed, it is now up to users to share information.

“People usually don’t share boring news with boring facts,” said Filip Struharik, the social media editor of Denník N, a Slovakian subscription news site that saw a 30 percent drop in Facebook engagement after the changes. Mr. Struharik, who has been cataloging the effects of Facebook Explore through a monthly tally, has noted a steady rise in engagement on sites that publish fake or sensationalist news.