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."
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.
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.
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.
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.
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.