Recent years have seen a surge in people using wearable fitness trackers to help them lose weight. But these devices may not actually be helping people get in shape, according to new research whose findings were released Tuesday.

Researchers of the study, which was published in the Journal of the American Medical Association, assigned 470 obese or overweight people a low-calorie diet and more physical activity along with group-counseling sessions on health and nutrition. After six months into the weight loss program, the participants were divided into two groups — one that received fitness trackers to be worn on the upper arm and the other that continued the counseling sessions.

Upon the completion of the study — a total of two years — researchers found that those given the trackers lost 7.7 pounds weight on average, while participants in the other group reported an average weight loss of 13 pounds. Researchers used BodyMedia Fit activity trackers that were commonplace when the study started.

“While usage of wearable devices is currently a popular method to track physical activity — steps taken per day or calories burned during a workout — our findings show that adding them to behavioral counseling weight loss that includes physical activity and reduced calorie intake does not improve weight loss or physical activity engagement. Therefore, within this context, these devices should not be relied upon as tools for weight management in place of effective behavioral counseling for physical activity and diet,” John Jakicic, the study’s lead author and chair of University of Pittsburgh’s Department of Health and Physical Activity, said in a statement.

But why do wearable fitness trackers not aid in weight loss? Jakicic theorized that the people who relied on these devices developed a false sense of security that whatever workout they did in a day was enough and that they could relax their diet restrictions. He also suggested that participants in the study may simply have not been encouraged enough by the wearable trackers to exercise or follow their diet.

“These are people who are already struggling, and already don’t like activity,” he told Time. “They look down and see, ‘I am so far away from my goal today, I can’t do it.’ It could be working against them.”

Jakicic also noted that the BodyMedia Fit device his team used in the study may be a loophole in their analysis since it calculated the heat generated by exercise to estimate physical activity, rather than measure the heart rate, which several of fitness trackers today do.

“We are going to get criticized for that, but at the end of the day, there are studies that show that after a few months people get bored with them,” Jakicic told the magazine.