Young dieters following "clean eating" regimes that cut out dairy produce face developing osteoporosis in later life, a charity has warned.
A National Osteoporosis Society (NOS) survey found four in 10 young adults have tried the fashionable diets that often involve avoiding dairy, gluten, grain and sugar, while more than fifth had severely restricted their intake of milk and cheese.
Fuelled by social media, the clean eating trend has surged in popularity in recent years, with some advocates achieving celebrity status with hundreds of thousands of followers.
However the charity warned that restrictive diets among younger generations will lead to widespread health issues in later life, including osteoporosis which causes bones to become brittle and break.
Charity adviser Professor Susan Lanham-New told the Daily Telegraph: "By the time we get into our late twenties it is too late to reverse the damage caused by nutrient deficiencies.
"Without urgent action being taken to encourage young adults to incorporate all food groups into their diets and avoid clean eating regimes, we are facing a future where broken bones will become the norm.
"Osteoporosis is a painful and debilitating condition and young adults have just one chance to build strong bones."
The NOS surveyed more than 2,000 adults and found 70% of those aged 18 to 35 were on or had been on a diet and 18 to 24-year-olds were most likely to have tried clean eating.
The diets often focus on avoiding processed foods and eating raw, unrefined produce.
Dairy foods are a source of calcium, an essential nutrient for the health and strength of bones.
The NOS campaign, A Message to My Younger Self, is being supported by nutrition expert and skincare guru Liz Earle.
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."