For decades Germans have extolled the benefits of free body culture – or being naked in nature. But a German sexologist has claimed that the practice of FKK, as it is widely known, is dying out due to a new “nudity taboo”.

Once a focal point of German bathing culture, FKK has been pushed to the margins of most of Germany’s beaches and lakesides, according to the author Kurt Starke.

“FKK is no longer a trend,” he states in a new book, Nudity Congestion, in which he argues that a practice that once dominated large parts of German holiday resorts is now considered old-fashioned and too regulated. “Now stretches of beach dedicated to FKK are reduced and often even combined with the stretches of beach reserved for dog walkers.”

The movement has its roots in the late 19th century when it was promoted as a healthy lifestyle, particularly for workers. The first FKK beach appeared on the North Sea coast 100 years ago. For more than 70 years entire sections of beaches, lakesides and campsites have been reserved by law for those who choose to be naked, and the practice – with its strict rejection of any shame about nudity – has seeped into the national psyche.

The Nazis largely suppressed it. Revived again after the second world war, in the 1970s the FKK movement attracted its largest number of followers.

Starke says that FKK, the first movement of its kind in the world, led to a widespread acceptance of public nudity without an overt connection to sexuality, which is reflected in Germans’ relatively relaxed attitudes to nudity.

But it was in the former communist east, the GDR, that its impact was most felt. There authorities positively encouraged it, particularly among the proletariat. While swimming aids such as lilos, rings and dinghies were banned for fear people might try to escape by sea to neighbouring Denmark, nudity was positively encouraged.

For Christian Utecht, president of the Association of Free Body Culture for Berlin and Brandenburg, which has 3292 members, those who argue FKK is a dying trend are missing the bigger picture.

“For sure, the movement’s been hopelessly ageing for years, but those who follow it are complete advocates of it, and increasingly young families with children are now joining,” he said.

He blames a drop in membership on a social media-driven desire for the perfect body as well as a more multicultural society where newcomers are not so willing to accept the FKKlers’ acceptance of public nudity.

Utecht, from western Germany, admits he was “not born an FKKler” – the name given to followers of the movement – but was introduced to it by his parents. He liked it, he says, because “I don’t like wearing wet swimming trunks”. His association hosts flea markets, summer camps, fun-runs and even open days. And it extols the health benefits of FKK, such as the promotion of exercise and being outdoors.

“We have members in their 80s who are extremely active,” Utecht said. FKK is also a great leveller, he argued. “You never know if the naked person next to you is a doctor or a car park attendant, and it really doesn’t matter.”

Nationwide the FKK association has about 32,000 members, a number that has halved since 1980.

But those naturist organisations seeing a growth in their membership are those that combine sport and nudity, such as the Adolf Koch Association in Berlin, named after one of the main founders of FKK, which offers everything from nude volleyball to nude yoga and has doubled its membership in the past two years. In the summer months club members meet outside; in winter, in a sports hall. Knee pads and other protective clothing is allowed, shorts are not. Neither is the taking of photographs.

Antje Schmid, 37, who holidays every year on an island off Germany’s Baltic coast in what was once communist east Germany, insisted she did not need an organisation to enjoy FKK. “I grew up in east Germany, and am just about old enough to remember when this very beach was full of FKKlers and anyone who wore clothes stood out,” said the sales assistant. “There is a freedom attached to going FKK, which is quite indescribable if you’re not accustomed to it. People are definitely now more reluctant to do it.”

Gazing across a sandy beach bustling with holidaymakers who seemed split almost equally between the nude and non-nude, she added: “I just cannot imagine it dying out.”

Utecht says membership drops off most strongly among those aged between 18 and 30. “That’s when they’re most image conscious, I suppose,” he said. “But they tend to come back when they’re in their 40s and not so concerned about how they look, but wanting to show their young children the benefits.”

It took years for the movements in the former east and west of Germany to find any sort of common ground, Utecht admited. “Even now I know little about the experiences of east German FKKlers. But where we are all in agreement is that we’re happiest in our birthday suits and we’re keen to quash any nudity taboos.”