Doctors warn fitness trackers can cause activity-based anorexia

Some doctors are concerned that fitness tracking devices - like Fitbit - could be dangerous to our health.

More than 400,000 Kiwis over the age of 15 use fitness trackers. While they can be motivational, some experts say getting addicted to them can become an obsession with life-threatening consequences.

"These types of technologies can be quite harmful and heighten particular obsessive traits toward exercise and eating," says Waikato University sociology of sports Professor Holly Thorpe.

Prof Thorpe says the new technology which shows how many calories you've burned or how many steps you've taken is part of the issue.

"In the past we might have gone for a run, we might have done it for the joy of it. Now people go for a run and they've got to make sure they're getting that data," she says.

An eating disorder specialist says that can be particularly harmful and that using fitness devices can cause some people to develop what's known as activity-based anorexia.

"The activity and exercise aspect is usually the most challenging to treat," Dr Roger Mysliwiec told Newshub.

Those most at risk from activity-based anorexia include people with a family history of the illness or who have an anxiety disorder or a history of dieting.

He says the illness has been simulated in rats - including an experiment where one exercised until it died.

"I think it's a very powerful illustration of how dangerous it is to get into that kind of running addiction," Dr Mysliwiec says.

Doctors say while exercise is important - it shouldn't all be about counting calories or steps. And users need to ask themselves - is it empowering, or is it controlling them.