Alternative investments have been allowed within IRAs since the 1970s, when they were first introduced, but most companies have focused on stocks, bonds and mutual funds. As the markets continue to fluctuate, more investors are turning to options they can fully control themselves, like self-directed IRAs and solo 401(k)s.

Adam Bergman, a tax attorney and partner at IRA Financial Group in New York and Florida, says that interest in self-directed retirement account options has "exploded in popularity" the past few years. He believes they are getting more notice now because people began looking for alternative ways to invest after the 2008 stock market decline.

"People aren't as comfortable having all of their retirement fund in stocks or Wall Street. They are looking to diversify with gold, real estate, peer-to-peer lending or investing in a friend's business," he said.