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.
A bogus news story that spread in December illustrates the problem, Mr. Struharik said. The story claimed that a Muslim man had thanked a good Samaritan for returning his lost wallet, and had warned the Samaritan of a terrorist attack that was planned at a Christmas market.
The fabricated story circulated so widely that the local police issued a statement saying it wasn’t true. But when the police went to issue the warning on Facebook, they found that the message — unlike the fake news story they meant to combat — could no longer appear on News Feed because it came from an official account.
Facebook explained its goals for the Explore program in Slovakia, Sri Lanka, Cambodia, Bolivia, Guatemala and Serbia in a blog post in October. “The goal of this test is to understand if people prefer to have separate places for personal and public content,” wrote Adam Mosseri, head of Facebook’s News Feed. “There is no current plan to roll this out beyond these test countries.”
The company did not respond to a list of questions about the Explore program, but Mr. Mosseri said in a statement on Friday that the company took its role as a “global platform for information” seriously.
“We have a responsibility to the people who read, watch and share news on Facebook, and every test is done with that responsibility in mind,” he said.
The impact of the changes to the News Feed were also felt in Cambodia. Months into the experiment (Facebook hasn’t said when it will end), Cambodians still don’t know where to find trusted, established news on Facebook, said Stuart White, editor of The Phnom Penh Post, an English-language newspaper.
Nongovernmental organizations working on issues like education and health care also complained that the changes broke down lines of communication to Cambodians in need.
Facebook has become particularly important in Cambodia. The country’s leader, Hun Sen, has cracked down on political opponents, activists and media, effectively transforming the struggling democracy into a one-party state. Journalists have been arrested, newspapers have been shut down, and Facebook has emerged as an important, more independent channel for information.
That is, if you can find that information. Mr. White recalled a conversation this month with a friend who casually observed the lack of political conversation on Facebook.
“He said he thought the government had banned politics on Facebook,” Mr. White said. “He had no idea that Facebook had created Explore or was placing news there. He’s a young, urbanite, English-speaking Cambodian. If he didn’t know about it, what do you think the effects are on other parts of the country?”
In Bolivia, the alterations to the News Feed also occurred in a country where the government and the press have found themselves at odds, with news sites like Página Siete frequently criticizing Mr. Morales, a left-wing populist who has accumulated enormous power since being elected president in 2006.
“We became the only media to take on the government,” said Rodolfo Huallpa, the web editor of Página Siete. Half of the site’s traffic came from social media, with the lion’s share of that from Facebook, he said. Since Explore was introduced, overall web traffic to the site has dropped 20 percent.
The loss of visitors from Facebook was readily apparent in October, and Mr. Huallpa could communicate with Facebook only through a customer service form letter. He received an automatic reply in return.
After complaints from other outlets, Facebook eventually released a statement on a blog in Spanish explaining the Explore feature and the testing being done in Bolivia and other countries. But Facebook offered no means to contact it, Mr. Huallpa said.
“We can’t talk to Zuckerberg, we can’t even talk to a customer service representative,” said Isabel Mercado, the editor of Página Siete, referring to Facebook’s chief executive, Mark Zuckerberg.
The Explore experiment has reduced traffic by 30 to 60 percent at the website of Los Tiempos, the main newspaper of Cochabamba, the country’s fourth-largest city, said Fabiola Chambi, the publication’s web editor.
Ms. Chambi, however, fears the main consequence of the Explore function will be deepening polarization in a country already divided by ideology. “It’s good to see things from your friends and your family, but there needs to be diversity of information,” she said. “The miscellany is good.”
Bolivia has also seen an increase in fake news as the established news sites are tucked behind the Explore function.
During nationwide judicial elections in December, one post widely shared on Facebook claimed to be from an election official saying votes would be valid only if an X was marked next to the candidate’s name. Another post that day said government officials had put pens with erasable ink in the voting booths.
Vladimir Tirado, a social media expert in Bolivia, said the government might simply begin paying for posts to appear on users’ News Feeds, an option that he said most newsrooms could not afford.
“Whoever has more money will appear more,” Mr. Tirado said. “In this sense, the government will certainly win.”
Ms. Chambi of Los Tiempos said her newsroom hardly had enough money to pay its journalists to report stories, let alone to distribute them as paid posts on Facebook. The situation has left her uneasy about the role that the tech giant may play in her country.
“It’s a private company — they have the right to do as they please, of course,” she said. “But the first question we asked is ‘Why Bolivia?’ And we don’t even have the possibility of asking why. Why us?”