Before developing anorexia, she had weighed about eight stone (50.8 kilograms). By the time the eating disorder landed her in hospital, she was four-and-a-half stone (25.4kg).
About 1.25 million people in the UK are believed to have an eating disorder, according to the charity Beat.
And though Britons have become far better at discussing mental health problems in recent years, there remains a particular stigma around eating disorders.
The 'Diana effect'
The subject is being brought to the fore by the new series of The Crown, which was aired this weekend, and depicts graphic scenes of Princess Diana's struggles with bulimia.
The Princess of Wales' decision to speak out about her "secret disease" shed new light on the taboo subject of eating disorders.
"You inflict it upon yourself because your self-esteem is at a low ebb, and you don't think you're worthy or valuable," she said in her famously candid Panorama interview in 1995.
It would ease the way for others to speak out and seek help, in what became known as the "Diana effect".
Though public perceptions have improved since, the numbers affected by eating disorders continues to rise and the diagnosis still carries a sense of shame and stigma, sometimes born of a misplaced belief that somehow sufferers are "choosing" disordered eating.
This is particularly true when an eating disorder develops in adulthood, as it did in Diana's case.
'I'm old enough to know better'
For Yates, now 46 and living in Cambridge, the age at which she presented with symptoms did affect the way she was treated.
"I went to see a GP and it wasn't a good experience," she says. "She told me, 'if you were a teenager I'd refer you to the eating disorder service, but you're an adult, so it's your choice to eat or not'.
"I did think, 'I'm old enough to know better, this shouldn't be happening to me'."
As an adult living alone, she was able to conceal what she ate. "People could see I was still working and functioning well. Friends told me afterwards I was so independent and such a strong woman, they didn't really believe what they were thinking when they saw my weight loss."
Still, she insisted on being referred to an eating disorder service and was put on a waiting list several months long for outpatient treatment.
She grew addicted to visiting the gym, where she "discovered there was this amazing world where you could watch the number of calories you'd burned on the treadmill and translate that into extra calories [to eat] that evening.
"Then I thought, 'if I don't eat more, I'll feel even better tomorrow', and it just spiralled. It was completely out of my control".
Her illness worsened as the years went on until she went to her GP and was immediately referred to an eating disorder service, but had to wait for treatment.
In the meantime, her weight plummeted further – the only clothes that would fit her were children's ones.
Services and campaigns are, she says, "all very much geared to prevention and young people and it's almost like 'oh, sorry we missed you'".
The shame barrier
Acknowledging that you have an eating disorder can be hard in adulthood, says Dr Bijal Chheda-Varma, a chartered psychologist and cognitive behavioural therapist.
"It's very shame-based... The key issue is that it's the shame that stops people from coming to clinicians."
Each time a celebrity shares their own struggles with a mental illness, as Diana did, clinicians do see a slight uptick in those with symptoms coming forward, she says.
"But there is a taboo. The most unfortunate myth is [eating disorders] are ... vanity-based, when there's such a range of complexity.
"I've sometimes heard dads of teenage girls or partners of adult women [saying to them] 'What's not to understand? Just eat healthily!' "
In fact, such illnesses are born of a desire to regulate emotions with food; a need for control and a yearning for numbness, she explains.
"The complexity increases with adulthood because we then need to look at what could have triggered it," she says. "Adults become high-functioning; they may be holding down jobs and be married with families. Life becomes more complex."
Treatment, as well as public perception, has improved in the years since Diana spoke out. Where once people were admitted to hospital, often far away from home and for long periods of time, there is now a greater understanding of the value of community treatment instead; of keeping people with their families and social networks.
Yates is a healthy weight today, but still struggles with binge-eating.
'I'd never had any hang-ups'
Experts say the Diana effect endures to this day – and hope the modern retelling of her experiences in The Crown will help to improve understanding of eating disorders.
"[Meanwhile] my weight continued to slip down," says Yates. "I became physically ill. I was so weak ... I was staying with my mum and she had to lift a cup to my lips. I was very sleepy, I couldn't do anything for myself."
At that point she contacted the eating disorder service and was admitted to hospital in London a few days later. "I was lucky to stay alive for those few days," she says.
She remained in hospital for 10 months, until her heart was stable enough for outpatient treatment.
But she'd "never fully dealt with the psychological issues", she says. "So I began binge-eating and for a period suffered from bulimia. I was trying to make myself vomit about 100 times a day."
Rhiannon Pursall, from Warwick, also knows what it's like to watch yourself slide into disordered eating during adulthood.
Now 35, she was in her early 20s and at Sheffield University when it started. "I'd never had any hang-ups about my body or food," she says.
"[But] I always had that feeling of being not quite sure I was good enough in many areas, and during third year I found myself comparing myself a lot to other girls... There was a sense of comparison and wanting to better myself."
Pursall is currently recovering.
Where to get help:
• 0800 543 354 (0800 LIFELINE) or free text 4357 (HELP) (available 24/7)
• https://www.lifeline.org.nz/services/suicide-crisis-helpline
• YOUTHLINE: 0800 376 633
• NEED TO TALK? Free call or text 1737 (available 24/7)
• KIDSLINE: 0800 543 754 (available 24/7)
• WHATSUP: 0800 942 8787 (1pm to 11pm)
• DEPRESSION HELPLINE: 0800 111 757 or TEXT 4202
• NATIONAL ANXIETY 24 HR HELPLINE: 0800 269 4389
