When did dairy – a one-time health staple, along with vegetables and protein – get tarred with the same brush as alcohol and sugar?
"A lot of young women now get their health advice from Instagram, which has developed a fairly insidious anti-dairy message in the last few years," says dietitian Helen Bond.
"Subtle hashtags like #dairyfree and #milkalternatives are scattered around glossy-looking posts, and the move towards plant-based eating and veganism has exacerbated things. Then there's the ethical concerns over the dairy industry, which are understandably turning people off.
The Duchess of Cornwall last week took aim at "ridiculous dieting" and "cutting out dairy", at a reception for the Royal Osteoporosis Society.
"These girls see skinny Lizzies in a magazine and they all want to be thin. It's about social media, too," said the duchess, whose mother, the Honourable Rosalind Shand, died from osteoporosis in 1994 when she was just 71 - the age Camilla is now.
Her maternal grandmother, Sonia Keppel, had also died of the condition eight years earlier.
"Part of the problem now is the wartime generation who didn't have milk and butter because of rationing, so in their teenage years they deprived their bodies of calcium," continued Camilla.
"But that wasn't by choice. Teenagers have the choice now, and still seem to be depriving their bodies. It's the fad diets, they are the worst thing to do. You are depriving your bones of calcium.
"We need to find a way of educating children that they need to take care of their bodies now, instead of aspiring to look like someone they see in a picture, if they want to protect themselves in old age."
Osteoporosis is a bone disease that occurs when the body loses too much bone, makes too little bone, or both.
It is common among women who have experienced menopause, because oestrogen plays an important role in maintaining the balancing act of this process, known as bone remodelling. Although the UK's Royal Osteoporosis Society reports the number of sufferers in their teens, 20s and 30s is increasing.
Osteoporosis New Zealand estimates that by 2020 the number of osteoparatic fractures will rise to 116,000 a year, compared with 84,000 in 2007 - and the cost of managing them will be $400 million, although the total ongoing cost of treating people with osteoporosis is much higher - we spend about $1 billion a year.
A new study in the UK found 20 per cent of 18- to 35-year-olds have severely restricted their intake of dairy in the past few years.
Like Camilla, some experts point the finger of blame at the superfood stars of social media, many of whom claim giving up dairy has helped them lose weight and boost their energy levels. There are currently 8.5 million (and counting) #dairyfree hashtags on Instagram alone.
But it's not just impressionable teenagers cutting out dairy in droves. In 2017, Samantha Cameron told an interviewer: "I've been on a no wheat, no sugar, no dairy products, no alcohol diet. Dave [her husband and former prime minister] gave up on the diet on day three, but I have stuck it out all the way through January."
Victoria Beckham also avoids dairy, and Gwyneth Paltrow's chef has revealed the star avoids, "any sugars, anything sweet, no dairy".
There will be "a generation of young girls and women who aren't storing enough calcium to see them through to old age" if things don't improves, says Bond.
"You need to bank a lot of bone in your teens and 20s. It's too late to turn 60 and decide to improve your bone health. Osteoporosis is often described as a silent epidemic because it only shows itself when much of the damage has been done."
If you're going to cut out dairy, says Bond, you need to ensure you're getting calcium elsewhere - via oily fish with small bones in it, like sardines, vitamin D and iron-rich foods, dark green vegetables, dried fruits and milk alternatives like soya or hazelnut.
"And if you don't need to cut out dairy for health or ethical reasons, then do dairy better. Go back-to-basic with full fat, organic milk, unsweetened Greek yoghurt, good quality cheese and organic butter. I think a lot of dairy's worsening reputation has come from the pink sweetened yoghurts and large, syrupy lattes you see around. An organic full-fat latte, a matchbox-sized chunk of good cheese and a small pot of Greek yoghurt is a great daily hit of dairy."
Of young women's attitudes to dairy, Camilla told the conference: "You feel like you are invincible, and it's about what you look like. Food becomes about what your figure is like, not what it is doing for your body."
She said watching their grandmother die caused her own children, Tom and Laura, to become aware of bone health from a young age: "They were horrified by seeing my mother getting smaller and smaller. They worshipped her. Suddenly, they saw this tiny woman stooped in agony. It is something they will remember for the rest of their lives. But people who haven't seen their parents or grandparents like that will think: 'We're never going to get that.' It's the immediacy of youth."
Karen Dowers says she "absolutely agrees" with the Duchess of Cornwall. "I talk to everybody I know about this, particularly friends with children, to raise awareness of bone health."
Two years ago, Dowers, then 37, was taking part in a triathlon when she fell off her bike. "It wasn't a particularly bad fall, but the pain was excruciating. I cycled another hundred yards, but when I got off my bike, I couldn't stand and realised something was badly wrong."
Dowers, a biologist at the University of Dundee, had broken her leg, was diagnosed with osteoporosis – and told she had the bones of a 75-year-old.
"The doctors asked if I'd broken anything before and I told them I'd recently slipped on some ice and broken my elbow and several ribs, which concerned them. My paternal grandmother had osteoporosis, and I know there's a genetic link. But in my case, diet played a huge part."
Dowers, now 39, admits she had an unhealthy relationship with food in her teens and twenties.
"When I was 13, I started eating less and making myself sick when I got to school. I was never drastically skinny – I didn't want my parents to know anything was wrong – but I was a very controlled eater. I was a nervous child, I got picked on, and any big event sent my stress levels through the roof. I was also obsessed with how I looked, with quite bad body insecurities. Controlling what I ate helped me control my anxieties."
At 16, Dowers went on holiday to Singapore and picked up a stomach bug that led to IBS (irritable bowel syndrome). "I saw a nutritionist at university who suggested cutting out dairy. There weren't many milk alternatives back then, and I was a student so I didn't listen to the advice about getting calcium from other sources. Plus, I was still cautious of my weight, so I was happy to cut something out. I was also drinking quite a bit, which I now know is also bad for bone health."
By her 30s, her eating issues had resolved and Karen regularly took part in fun runs and triathlons. "When I was training for the triathlon I thought I had shin splints, but the doctor who diagnosed me said it was, in fact, a hairline fracture, so the break was just waiting to happen. I was 37 and my bone score should have been zero; anything less is 2.5 is osteoporosis. My score was minus 3.1, the equivalent of a 75-year-old."
In the past two years, Dowers has been put on calcium and vitamin D tablets, collagen supplements, reduced her alcohol intake and eats plenty of non-dairy ("it still triggers my IBS") calcium alternatives, and has reversed her condition to osteopenia, a slightly less serious precursor to osteoporosis.
"Young women like me are taught to think about their hearts and breast cancer risk, but not their bones. I hate to think of the damage I did to mine through faddy eating."
How can I protect my bones if I don't do dairy?
•Choose nourishing drinks, such as smoothies, fortified milk alternatives or hot chocolate
•Use soya alternatives to meat, yoghurt, milk and custard
•Add soya cream alternative to porridge
•Add peanut butter to smoothies
•Add cashew nuts or silken tofu to soups and blend
•Use crumbled tofu and vegan mayonnaise as a sandwich filling
•Add olive oil to vegetables
•Add vegan spread to potato
•For more advice on protecting your bone health, visit The Royal Osteoporosis Society
SOURCE: The UK's Vegan Society