A cult of clean eating is a "ticking timebomb" that could leave young people with weak bones, the National Osteoporosis Society has warned.

Research by the charity shows that four in ten of those aged between 18 and 24 have tried such regimes, which are now coming under attack for cutting out major food groups, such as dairy.

The diets have become increasingly fashionable, and are associated with a number of celebrities, who have boasted how they have cut out gluten, dairy, grains and refined sugars.

But the charity said many of those following the trends had no idea that cutting out major food groups could jeopardise their long-term health, with bones still developing in early adulthood.

The craze has been associated with a number of celebrities - many of whom have now moved to disassociate themselves from such habits - as well as on social media.

Earlier this year London sisters Jasmine and Melissa Hemsley moved to distance themselves from "clean eating", saying their emphasis was on eating foods without additives, not on restriction.

But the charity's survey of more than 2,000 adults found 70 per cent of those aged between 18 and 35 are or have been on a diet, with those aged between 18 and 24 most likely to have tried "clean eating".

Dairy - a major source of calcium, which protects the bones - was one of the key food groups targeted.

In total more than 20 per cent of those such age had cut or severely restricted intake of milk or cheese.

This group were far more likely than older adults to be getting their information about health and diets from blogs, vlogs and other social media.

Experts said the trends were putting the generation at significant risk of developing osteoporosis - a condition that causes bones to become fragile and break easily - in later life.

Professor Susan Lanham-New, Clinical Advisor to the National Osteoporosis Society and Professor of Nutrition at the University of Surrey, says: "Diet in early adulthood is so important because by the time we get into our late twenties it is too late to reverse the damage caused by poor diet and nutrient deficiencies and the opportunity to build strong bones has passed."

Half of all women and one in five men develop osteoporosis after the age of 50. Broken bones, also known as fractures, caused by osteoporosis can be very painful and slow to recover from.

A poor diet for those in their teens and early twenties now could see a significant rise in the numbers of people suffering fractures and the complications associated with them in the future.

Professor Lanham-New said: "Without urgent action being taken to encourage young adults to incorporate all food groups into their diets and avoid particular 'clean eating' regimes, we are facing a future where broken bones will become just the 'norm'.

"We know that osteoporosis is a painful and debilitating condition and young adults have just one chance to build strong bones and reduce their risk of developing severe problems in later life."

The charity is urging parents and grandparents to talk to young people about the risks from their diet.

The campaign, called "A Message to My Younger Self" is being led by wellbeing and beauty expert Liz Earle, who said she feared the pressures on her own daughters from social media.

She said: "When I was growing up, my meals weren't photographed and shared on social media. The pressure young women are under to match what their idols on Instagram are eating is really high."