Religion 'rules sex belief, not actions'

God may influence Australians' attitudes towards sex but religion plays little role in what they actually do in bed, a landmark survey has found.

The study of almost 20,000 Australians has revealed that most who hold religious beliefs have strong negative attitudes towards watching X-rated films, cheating and sex before marriage.

However, unless they were very strong believers, their attitudes didn't appear to stop them doing these things themselves, the researchers found.

"What we saw was when it came to these sexual issues, people influenced by religion believed one thing but did another," said lead researcher and psychologist Dr Richard de Visser.

Researchers used Australia's largest ever social survey to glean the first snapshot of the links between religion, sexual beliefs and actual behaviour.

The findings will be presented to hundreds of sexologists at the World Congress on Sexual Health in Sydney this week.

They found that, generally, those with the strongest beliefs were less likely to either support or go through with abortions, sex before marriage, cheating or the watching X-rated films.

They also were less likely to support homosexuality or report homosexual behaviour, said Dr de Visser, formerly of La Trobe University but now based at the University of Sussex in the UK.

People with less strict religious beliefs - those who attended a service less than monthly - held similar beliefs to those who went more often.

But when it came to behaviour they were in line with people who had no religious beliefs at all, he said.

"We found it very interesting that people make such a strong distinction between what they think they should do and what they're prepared to do," the researcher said.

The religious groups included protestants, Catholics, muslims and Buddhists; Buddhists showing the most "relaxed" sexual attitudes and behaviour overall.

Dr de Visser said the results showed the influence of religion on life was more subtle in Australia compared with the US but the influence of these beliefs on attitudes was stronger than many realised.