A startling number of Japanese youths have turned their backs on sex and relationships, a new survey has found.

The survey, conducted by the Japan Family Planning Association, found that 36% of males aged 16 to 19 said that they had "no interest" in or even "despised" sex. That's almost a 19% increase since the survey was last conducted in 2008.

If that's not bad enough, The Wall Street Journal reports that a whopping 59% of female respondents aged 16 to 19 said they were uninterested in or averse to sex, a near 12% increase since 2008.

The survey paints a bleak picture for Japan's aging population. The Associated Press reports that the national population of 128 million will have shrunk by one-third by 2060 and seniors will account for 40 percent of people, placing a greater burden on the work force population to support the country's social security and tax systems.

Many commentators in the Japanese and international media have laid the problem squarely at the feet of soshoku danshi -- "herbivore men" -- a term coined by pop culture columnist Maki Fukasawa in 2006. It refers to Japanese young men who have rejected their culture's traditional definition of masculinity, and seemingly eschew relationships with the opposite sex as part.

CNN spoke to a Midori Saida, a 24-year-old Japanese woman who described "herbivore men" as "flaky and weak."

"We like manly men," she said. "We are not interested in those boys -- at all."

BBC News spoke to one such "herbivore" man (see video above). The man, Yusaki Yakahashi said: "Building a relationship seems like too much effort. To get her to like me and for me to like her... I'd have to give up everything I do at the weekend for her. I don't want to do that."

Another theory that seeks to explain Japan's shrinking population is that Japanese youth spend too much time engaged with technology, living in virtual worlds or settling for virtual girlfriends rather than real ones.

Britain's Daily Telegraph reports that Japan's government has undertaken a series of campaigns to encourage couples to have more children -- including making companies insist that their staff leave work at 6 pm to increase child allowances -- but according to Dr. Kunio Kitamura, head of the Japan Family Planning Association, "none of that is gong to have an impact if people are not going to have sex."