Timothy Kurek, a conservative Christian from Nashville, said the experience changed his views.
In an interview with MSNBC, Kurek said he even told his family he was a homosexual. He described that as "the most fearful thing I've ever done."
"I had to know what it was like to face that kind of potential excommunication," he said.
While his family was loving and supportive, Kurek said he knows many homosexuals have had different experiences.
That includes the friend who first inspired his project, who came to him in tears because she felt she had been "excommunicated" from family, friends and everything else in her life.
Kurek said he had been a "bigot" who was afraid of homosexuals. He decided to pose as gay for a year to see if there was anything he really needed to fear.
Kurek has written a book, which does not yet have a title. It is scheduled to be published in mid-October.
He said the book is not about what it is like to be gay in the United States or Tennessee.
"It's only about how the label of gay impacted my external life," he said.