Anna Boniface seemed to have the world at her feet when finishing as the 2017 London Marathon's fastest amateur female runner.
Her performance earned her an England team place in that autumn's Toronto Marathon. The then 25-year-old finished the London race in two hours, 37 minutes and travelled to Canada six months later.
But 10 miles into her international debut, Anna's ankle fractured.
"It was the breakthrough that broke me," she tells BBC 5 live Investigates.
"It was horrible, I'd never not finished a race in my life. I thought I could just struggle to the end somehow, but I realised I would not be able to go on, I just had to sit on the kerb and wait."
But worse was to come for the Reading runner. In addition to the stress fracture of her ankle, tests found poor bone density, including osteoporosis in her spine, which made fractures a real risk.
These symptoms were all hallmarks of a condition called Relative Energy Deficiency in Sport (Red-S).
This occurs when sports people restrict their diet in the belief that constant weight loss will keep improving performance, to such an extent that some of the body's functions begin to shut down.
The condition can cause a range of health problems in men and women including a drop in hormone levels, a deterioration in bone density, a drop in metabolic rate and mental health problems.
Anna, who works as a physiotherapist, admits she was aware of the condition but was so desperate to keep improving that she ignored the warning signs, which included not having a period for eight years.
"It was a lot to do with my training volume and not eating enough - not being wide enough in my food groups, being restrictive with carbohydrates," she says.
"I was training twice a day, I was running 100-plus miles a week at times, and you burn up a lot of energy with that, and from a runner's perspective you get it into your mind that you need to be this race weight.
"You get caught up in this cycle of running really fast, wanting to lose a little more weight, push that race weight a little bit more, running faster, and then just breaking, which is what happened."
The state of Anna's health was discovered before any more serious damage could be done and, after a year's rest, she has been able to slowly return to running.
Red-S can affect male and female athletes and became a recognised condition in 2014 - replacing another condition called female athlete triad, which recognised the affect of too few calories among sportswomen only.
There have been few studies into the prevalence of the condition but it is understood to be most common in sports such as athletics, cycling and dancing, where being light could make a significant difference to performance.
On Sunday, the #Trainbrave campaign is being launched to raise awareness of the risks of Red-S, particularly among promising amateur sportspeople who may be trying to improve their performance without giving enough thought to their diet.