FitBits, Jawbones, Apple Watches. Fitness trackers are everywhere these days and everyone – from super-toned gym bunnies to flabby middle-aged dads and even fashion editors – seems to have one.They're marketed as a way to help you lose weight, by enabling you to keep track of your steps, sleep and calorie intake (when paired with apps like MyFitnessPal).However, new research suggests they might not actually help us lose weight after all.A study by researchers from the University of Pittsburgh, published in the Journal of the American Medical Association , found that using fitness trackers as an aid to weight loss was no more beneficial than typical weight loss methods and may even make us gain weight.During the two-year study, 471 overweight young people (aged 18 to 25) were put on a low-calorie diet, a prescribed fitness plan and were asked to keep a diet diary and attend weekly group counselling sessions.After six months, everyone had lost weight – an average of between 7.7kg to 8.6kg.Then half the participants were given fitness trackers to use for 18 months, while the other half logged their activity using a website, a more typical dieting method.By the end of the study, the group using fitness trackers had lost less weight than the control group. They lost 3.5kg on average, while the group monitoring their progress online lost an average of 5.9kg.The results surprised the researchers and the data didn't make it clear exactly why using fitness trackers made dieters less likely to lose weight.One possible reason, said lead researcher Dr John Jakicic, is that the fitness tracker group may have been more likely to feel they owed themselves "treats" upon seeing their progress, leading them to lose less weight than the other group.There's also a chance they may have felt disheartened and given up early if they knew they weren't going to hit their daily goal.Jakicic said: “I think we have to be a little bit cautious about simply thinking that what we can do is just add technology to these already effective interventions and expect better results,” Ars Technica reported Some previous studies, by contrast, have found fitness trackers can promote weight loss, and Jakicic did acknowledge that these devices may be effective for certain people.Still, it's something to bear in mind before you invest in your own pricey little plastic personal trainer.