RIO DE JANEIRO, Aug 19 (Reuters) - Shareholders in Brazil's Petrobras have elected six government-affiliated nominees and two nominees affiliated with the market to serve on the company's board, the state-run oil firm said on Friday.

Overall, the number of board seats held by the state is unchanged, and the balance of power between the government and market shareholders in Petrobras was not modified. However, most government-affiliated board members, including the chairman, were swapped out, the company said in a statement describing the results of a Friday shareholders' meeting.

The effects of the long-awaited board shakeup were not immediately clear.

In the past, analysts and investors have cheered board elections for helping Petrobras move on from periods of management turmoil. But the board that was voted out had proved relatively adept at insulating Petrobras from political pressures, which have proven severe in the months leading up to Brazil's October presidential election.

Trailing in the polls, Brazilian President Jair Bolsonaro has frequently called on the company to bring down fuel prices and has criticized what he alleges to be excessive profits.

One Sao Paulo-based investor consulted by Reuters, who requested anonymity to speak frankly about the firm, said the board election was not seen as a pivotal event by the market.

"All eyes are on the (presidential) election," he said.

Of the six government-affiliated board members heading into the meeting, only one, current Chief Executive Caio Paes de Andrade, was re-elected.

Shareholders did not re-elect board chairman Marcio Weber. He will be replaced with Gileno Gurjao Barreto, the president of Serpro, a state company involved in information technology, Petrobras said.

Two market-affiliated board members were not up for re-election, nor was the sole board seat held by Petrobras workers, meaning the company's 11-seat board remains composed of six government-affiliated members, four market-affiliated members and one worker-affiliated member.

Bolsonaro's government had indicated in May it wanted to shake up Petrobras' board, though the meeting was delayed by a series of bureaucratic and procedural hurdles. (Reporting by Gram Slattery and Rafaella Barros in Rio de Janeiro; Additional reporting by Paula Laier in Sao Paulo; Editing by Tomasz Janowski, Matthew Lewis and Daniel Wallis)