Fitness trackers designed to help people keep in shape offer no useful weight-loss benefit, a study has suggested.

The two-year study of 471 overweight people found devices that monitor and provide feedback on physical activity - wearable technology such as fitness trackers, which are worn on the wrist like a watch - might not offer an advantage over standard behavioural weight-loss approaches.

Participants were placed on a low-calorie diet, prescribed increases in physical activity, and had group counselling sessions as part of the study, one of the first into the effectiveness of fitness trackers.

Six months into the study, half of the volunteers were given a fitness tracker to monitor their progress.

But researchers from the University of Pittsburgh found those provided with wearable technology lost less weight than the control group by the end of the trial.