Don't count on a fitness band or watch that tracks your activity to help you lose weight

High value
Evidence B
Saves money
Free
Takes minutes
No willpower

In plain words

Overweight people were given the same diet and exercise plan. After two years, the ones wearing an activity band had lost 3.5 kg and the ones not wearing one had lost 5.9 kg. If you want to lose weight, spending money on a device does not help; what works is the exercise itself.

Cost: The device costs 200 to 2000 CNY. You also spend attention every day looking at the data.
What you get: The IDEA trial enrolled 471 overweight or obese adults and followed them for 24 months. Everyone followed the same diet and exercise plan; the only difference was whether they wore a wearable device. The group that wore one lost 3.5 kg (95% CI 2.6–4.5, the plausible range). The group that did not wear one lost 5.9 kg (5.0–6.8), which is more. The gap between the groups was 2.4 kg (1.0–3.7, P=0.002). It looks like a good deal because “what gets measured gets managed” sounds reasonable, and you buy the device once and are done
Notes: This is a single trial, and it used an armband device from the early 2010s, so it cannot be used to say that “all wearable devices are useless.” Exercise itself works; see §2. The conclusion is just one sentence: if you want to lose weight, the device is not money you have to spend
Evidence grade: B : Supported by research but without a precise number, or based on small or single studies.
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

Translated from the Chinese original. Original book, section 6, tip 8. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer