Fitch Ratings is warning that Berkshire Hathaway Inc.'s deal for Burlington Northern Santa Fe Corp. could overexpose Warren Buffett's company to weaknesses in the economy at the expense of its more durable investments.The agency put Berkshire Hathaway rating's under review for a possible downgrade in the wake of its announcement Tuesday that it will buy the rest of the railroad company based in Texas for $26.3 billion.

The agency put Berkshire Hathaway rating's under review for a possible downgrade in the wake of its announcement Tuesday that it will buy the rest of the railroad company based in Texas for $26.3 billion.Fitch says the acquisition and Berkshire Hathaway's investments in utilities, energy and finance companies are shifting its asset profile toward businesses that use more financial leverage.

Fitch says the acquisition and Berkshire Hathaway's investments in utilities, energy and finance companies are shifting its asset profile toward businesses that use more financial leverage.