Don’t expect fitness trackers or smartwatches to help you lose weight

Cost: Devices cost between 200 and 2000 RMB. Plus, you have to constantly pay attention to the data they display every day.
In plain terms: 471 overweight adults followed the same diet and exercise plans. The group wearing fitness trackers lost just 3.5 kilograms over two years, while the group without devices actually lost 5.9 kilograms. Trackers do not aid weight loss; regular exercise itself is what makes the difference.
Benefit: The IDEA trial involved 471 overweight or obese adults and lasted 24 months. All participants followed identical diet and exercise regimens; the only difference was whether they wore wearable devices. Those wearing devices lost 3.5 kilograms (95% CI 2.6–4.5). The other group lost 5.9 kilograms (95% CI 5.0–6.8), a difference of 2.4 kilograms (95% CI 1.0–3.7; P=0.002). The devices seem cost-effective only because the idea that “quantification enables management” sounds logical, and they only require a one-time purchase.
Evidence grade: B
Sources:Jakicic JM et al. (2016). Effect of Wearable Technology Combined With a Lifestyle Intervention on Long-term Weight Loss: The IDEA Randomized Clinical Trial. JAMA. https://doi.org/10.1001/jama.2016.12858
Notes: This is based on just one trial using early 2010s wrist-worn devices, so we cannot claim that “all wearable devices are useless.” Exercise itself remains effective, as discussed in Section 2. This point simply emphasizes that buying such devices is not a necessary expense if your goal is weight loss.