Washington, USA - They are hiding in many bedrooms and in many major bookstores, unknown and unimagined by the public at large - Christian sex books. Though the phrase may not seem likely, in fact, dozens of titles aimed at helping married couples achieve better intimacy or work on their sexual technique have filled shelves since the 1970s and, judging by the amount of titles available, interest is not waning.
Amy DeRogatis, an associate professor of religion and American culture at Michigan State University, said she was surprised to find out how common such books were after a question by a student in a class on religion and sexuality prompted her to investigate the topic.
"Within the culture of evangelicalism these were very, very common," she said in an interview, noting she was most surprised that many of titles were hiding in plain view at the neighbourhood bookseller.
Contrary to the stereotype of puritanical sexual mores among the US Christian community, evangelical Christians have not shunned sex as purely functional, instead embracing it as a wonderful part of God's creation and urging a full sexual expression - within a monogamous marriage of course.
"I always thought that sex was one of the greatest gifts the almighty God could give to people," said Kevin Leman, a Christian pyschologist and author of several books about sex within marriage.
His books include Sheet Music: Uncovering The Secrets Of Sexual Intimacy In Marriage; and Sex Begins In The Kitchen: Creating Intimacy To Make Your Marriage Sizzle.
His writings and others like them focus on the importance of a husband and wife's relationship outside the bedroom and how it affects their sexual intimacy, as well as differences between the sexes that contribute to their attitudes about sex.
However, they don't shy away from giving hints about various positions or ways to spice up the love life.
The broad range of titles - like Red-Hot Monogamy by Bill and Pam Farrel and The Act Of Marriage by Tim LaHaye, novelist of the immensely popular Left Behind series based on apocalyptic prophesies, and his wife, Beverly - generally focus on traditional gender roles, which can prove problematic for those who fall outside the norm.
Still, they are often helpful for those who turn to their pages, DeRogatis said.
The books began to seriously appear in the 1970s about the time that sex manuals like the Joy Of Sex were sprouting up in the general culture, said DeRogatis, who has published an article about the works in the academic journal Church History.
But the authors of the Christian sex guides saw many of these works - with their anything-goes attitude and assumption that most readers would have more than one partner - as out of line with a God- ordained view of sexuality.
Their answer was to seek a biblical understanding of sex liberated from the puritanical rules viewed as de rigueur within the church, best summed up by the phrase "missionary position."
Unlike the mainstream sex manuals, the Christian sex books shy away from anything that could be perceived of as pornography, and thus shun most illustrations, DeRogatis said.
"We used to teach people essentially that sex was bad. If people are hung up on things, oh my goodness, it certainly is sex," Leman said in telephone interview. "I think it's refreshing to get people to see that sex can be great, it can be fun, it can be an integral part of a marriage."
That means that sex scandals from the pulpit - such as the 2006 case of Ted Haggard, a mega-church pastor in Colorado who preached against homosexuality yet visited a gay prostitute for years - don't tell the complete picture of sexuality among religious people, DeRogatis said.
"People get so caught up in sex scandals of celebrities within the evangelical culture, like Ted Haggard, that they see it as reflecting a broader hypocrisy with the culture and I don't think that's fair," she said.
Still, despite a growing number of resources available for Christian couples, with a slew of marriage retreats, more emphasis on the topic in premarital counseling and even a Christian website for buying sex toys, the topic hasn't exactly become a regular subject of Sunday sermons, even as it becomes less taboo.