Health experts and charities have warned people with eating disorders to "do anything you can to avoid" calorie counting apps.
They claim the devices, such as MyFitnessPal, can be dangerous for those trying to fight the mental illness.
Evie Walker became so unwell after using MyFitnessPal to record her food she could no longer walk to the shops - and was eventually hospitalised.
She has been living with an eating disorder for more than a decade. Dangerously underweight - she says she used the calorie counting app Myfitnesspal to record what she ate.
But, despite receiving a notice on the app telling her she had eaten below the recommended level she chose instead to use it as a badge of honour.
Evie says she's now using the App to try and regain weight. While many experts add that it can be used in a positive way to help those with, and without, eating disorders.
Renee McGregor, an eating disorder dietician, adds: "The problem with an eating disorder mindset is that they will always try and beat everything.
"That sense of undercutting almost feels like a badge of honour and it feels like I can survive on less than what everyone else is saying."
MyFitnessPal does have protective features - it warns those who record too few calories to review their goals.
It also restricts people from entering a target BMI below 18.5 - the level considered underweight.
Its parent company Under Armour says it's committed to encouraging healthy fitness goals, eating habits and weight management among its users.
Runner Amy Sole says the app left her in fear of eating more than her target calories for three years when she downloaded it while in the midst of an eating disorder.
She would often wake up in the night, trying to work out her meals in advance to ensure she only ate what was necessary.
Eating Disorder charities say more could be done to protect vulnerable users.
As the obsession of logging every single piece of food became too much, Amy sought medical care and is now recovered - but realises it could have been much worse.
She says she would warn others with eating disorders against calories counting apps:
"I'd say don't use it. It's the one that's probably worse for people than anything else I think. I lost five years of my life.
"I had things like my 30th Birthday, things that should have been a real celebration of your life and things and I missed it all.
"So that's the saddest thing, I'll never get that back."
- WATCH IN FULL: AN UNHEALTHY OBSESSION