More Americans have left Catholicism behind than any other religion in the U.S., according to a new report.

About 13 percent of American adults are former Catholics – people who were raised in the faith but now say they have no religion, or converted to Protestantism or other beliefs, according to a survey by Pew Research Center.

At the other end of the spectrum, 2 percent of U.S. adults report converting to Catholicism.

Pope Francis greets the faithful in Saint Peter's Square in Vatican City in September 2018

Overall, there are 6.5 former Catholics for every convert to the religion in the U.S. – a far higher ratio of losses than any other religion in the country, researchers found.

'It never connected with me,' said Oakdale, New York resident Aria Dapree, of leaving Catholicism. 'My mother actually taught religion in the house when I was young. It was weird stories. Jonah (and the whale), the Ark, all kinds of weird fantasy stories.'

The 62-year-old said 'inclusion' was the biggest reason she left the church, particularly Catholic opposition to homosexuality and the whole spectrum of lesbian, gay, bisexual and transgender people.

'Love thy neighbour? Well there's all kinds of neighbors,' Dapree said.

That attitude – and the 'culture wars' over sex before marriage and other choices that conflict with Catholicism – is a common reason people fall away from the church, said Dennis M. Doyle, a Catholic theologian and professor of religious studies at the University of Dayton.

'The secular world kind of grinds down the nature of religiousness and then with the culture wars a lot of outward manifestations of religion seem to appear more extreme,' he said.

'These have been very difficult issues for centuries in the Catholic Church,' he added. 'I don't think we (as Catholics) need to flip over and say, "Everything goes and let's reopen the bath houses for everybody," but I don't think it's as easy as "what we always thought is true."'

Many practicing American Catholics have beliefs that conflict with the Catholic Church

The American Catholic Church has more than 17,000 parishes across the country, with roughly 51 million adults – or one-fifth of the U.S. population – counting themselves as believers.

Catholics are spread across the country, with 27 percent living in the South, 26 percent in the Northeast, 26 percent in the West and 21 percent in the Midwest, according to Pew.

Even believers don't think everything is perfect, with 60 percent of Catholics saying they think the church should allow priests to marry and women to become priests.

In addition, nearly half of American Catholics believe that the church should recognize and accept gay marriage.

For some American Catholics, sex abuse scandals and the cover-ups that ensued may have been enough to drive them away, Doyle said, though it's unclear how many have left the church for that reason.

A bigger issue, Doyle said, has been a large cultural shift in which churches are no longer the primary social opportunity and glue for Americans.

'If you go back to the late 19th and the first half of the 20th century, Catholics were immigrants and they were the poor and there were great numbers of them, and they were mostly in the cities and they had this subculture that held them together,' he said.

Faithful pray during Sunday Mass at a Polish Catholic Church in Hamtramck, Michigan in 2016

'As Catholics became more educated and affluent overall, and as they become more oriented to the suburbs and less this great sociological mass in the cities, there's been a lot of social changes taking place,' Doyle added.

Another contributing factor has been the decreased enrolment in Catholic schools, said Sister Katarina Schuth, a professor emerita of the University of St. Thomas in St. Paul, Minnesota.

'Those who do attend elementary and secondary are much more likely to stay in the church because they know more about the church,' she said.

The 'rise of science' has also increasingly become the place where young Americans go for answers instead of the church, Schuth said.

She often speaks publicly about efforts to draw young people back into the church – something Schuth insists must be done in a respectful manner.

'Integrity is number one,' Schuth said. 'Just being open and listening to people, young people especially ... You don't have to be talking at them all the time.'