Peltz's Trian Fund Management disclosed a $3.5 billion stake in P&G this year and announced the nomination of Peltz to the company's board, setting off a bitter proxy battle with the maker of Crest toothpaste and Gillette razors.

"The addition of one well-qualified nominee, who holds a large economic stake, appears likely to have benefits that outweigh the potential risks," ISS said. "Support for dissident nominee Peltz is recommended."

P&G did not immediately return a request for comment.

The company has argued that Peltz's plan to boost shareholder value by organizing the company into three largely autonomous business units would result in higher costs, lower profits and another restructuring that could lead to a breakup of the company.

Last week Glass Lewis, another proxy advisory firm, recommended that shareholders vote in favor of Peltz.

Cincinnati-based P&G's annual shareholder meeting is scheduled for Oct. 10.

(Reporting by Carmel Crimmins and Carl O'Donnell; Editing by David Gregorio)