Watch in full: an Unhealthy Obsession
Apps and devices that record our exercise can be dangerous for those with eating disorders, experts have warned.
Many are warning those suffering not to use fitness trackers such as Fitbits, as they can often become an obsession - with life-threatening consequences.
Coralie Frost was suffering from an eating disorder when she says her life became controlled by her Fitbit for two years. Her weight became dangerously low.
The app gave her access to a dashboard, which told her the number of calories she was consuming and burning - and how many she should eat to keep to a certain weight.
But, Coralie says there was also no advice given, "You can log in straight away and set your own targets, there's nothing that flags to say you're over training, or you're underweight."
I was not qualified, as someone going through an eating disorder, to set what I thought should be my ideal goal as it would always be lower than what I should be for my age and height. What it did do was it fuelled my anorexia.
But it wasn't just Coralie's health that suffered, she slowly started separating herself from her friends and family.
Her addiction to the app - which was tracking everything including her sleep, meant she couldn't stop checking it at multiple times throughout the day.
I felt like that was my only friend, I was isolated with the app. It knew more about me than my friends and family did.
Eating disorder charities say they've seen numerous people who are addicted to fitness apps.
Tom Quinn from charity Beat, says perfectionist traits often exhibited by those with eating disorders can, "really take over" when it comes to these apps.
With individuals who are seeking, often to regain control - perhaps they have low self esteem, or they're stressed by other things in their life - actually that perfectionism, that desire to do everything right can really take over.
Coralie's weight is now stable, but for others the effect of fitness apps is still acute.
Zara Kindred, who has anorexia, grew obsessed with her Fitbit, trying to walk more and more steps each day.
The 20-year-old would set her alarm earlier every morning to ensure she was awake and moving straight away.
She became so underweight she needed emergency care.
It came to a point I was just so exhausted I couldn't do anymore. I was trying to walk crazy amounts of steps, I lost a lot of weight, and I just lost control really.
Fitbit does have a health warning in its manual, but it is below other guidance, including not to use the device in a sauna or steam room.
At Fitbit, our mission is to empower people to lead healthier, more active lives by providing them with the data, tools, inspiration and guidance to reach their health and wellness goals.
Coralie has now ditched her Fitbit and is fully recovered, but Zara is still very unwell, and trying to gain weight.
While she does her life is on hold, and she has a warning to others about using fitness trackers.