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Wearable activity tracker adherence associated with reduced body fat in a 12-month randomized trialWearable tracker use linked to lower body fat in overweight adults

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Key Takeaway
Consider wearable tracker adherence as a marker for reduced body fat in mHealth interventions.

This randomized controlled trial enrolled 502 participants. The population consisted of 79.5% female individuals with a mean age of 45 years and a mean BMI of 33.7 kg/m. The setting was not reported. The study examined associations between wearable activity tracker adherence and changes in percent body fat and sex-specific waist circumference. The intervention involved adherence to goals of at least 300 minutes per week of moderate-to-vigorous physical activity (MVPA). The comparator was not reported as a separate arm, as the study examined associations within the full sample of participants randomized to standard monitoring or standard monitoring plus feedback. The follow-up period was 12.0 months.

Primary outcome results showed that greater MVPA adherence was associated with reductions in body fat in the full sample. The effect size was b = -0.01 with a 95% CI of -0.02, -0.005. When analyzing only completers, higher adherence was associated with decreases in body fat. The effect size was b = -0.01 with a 95% CI of -0.02, -0.004.

Secondary outcomes included waist circumference measurements stratified by sex. In the full sample, waist circumference in women was not associated with adherence. The effect size was b = -0.01 with a 95% CI of -0.03, 0.01. In men, waist circumference was also not associated with adherence in the full sample. The effect size was b = -0.03 with a 95% CI of -0.05, 0.0002. Among completers, higher adherence was associated with decreases in waist circumference for women. The effect size was b = -0.02 with a 95% CI of -0.04, -0.004. For men who completed the study, higher adherence was associated with decreases in waist circumference. The effect size was b = -0.04 with a 95% CI of -0.08, -0.003.

Safety and tolerability findings were not reported. Adverse events, serious adverse events, discontinuations, and overall tolerability were not reported. The study did not provide data on specific adverse event rates or discontinuation reasons.

These results support the use of wearable-derived physical activity measures in long-term mHealth behavioral interventions. The findings suggest that tracking adherence to MVPA goals may be linked to improvements in body fat percentage. However, the association with waist circumference was inconsistent across the full sample and only emerged in the completer subgroup for both sexes.

Key methodological limitations include the lack of reported setting details and the absence of a distinct comparator group for direct comparison. The study examined associations rather than establishing causality. The certainty of the evidence was not reported. Potential biases related to participant retention are suggested by the difference in results between the full sample and the completer analysis.

Clinical implications suggest that wearable technology can be a useful tool for monitoring physical activity in obesity management. The data supports using these devices to track adherence to MVPA goals. However, clinicians should interpret waist circumference results with caution as associations were not consistent in the full sample.

Questions remain unanswered regarding the specific mechanisms driving the reduction in body fat. It is unclear if the feedback component was the primary driver of adherence. Further research is needed to confirm these findings in diverse populations and to determine long-term sustainability of these effects.

This research matters to people who want to manage their weight using technology. Many adults struggle with excess body fat and waist size. This study looked at whether using a wearable activity tracker helped people move more and lose fat over time. The goal was to see if setting movement goals on a device could lead to real changes in body composition.

The researchers studied 502 participants. Most were women, and the average age was 45 years. The group had a high average body mass index, indicating they were overweight or obese. Participants were part of a larger trial where some received standard monitoring and others received standard monitoring plus feedback. The focus here was on those who used a wearable tracker and aimed for at least 300 minutes of moderate-to-vigorous physical activity each week.

After 12 months, the team found that people who stuck to their movement goals had less body fat. The data showed a clear link between higher adherence to activity goals and reductions in percent body fat. However, the link to waist size was mixed. For women in the full group, waist circumference did not change with tracker use. For men in the full group, the link was also not clear. When looking only at participants who completed the study, both women and men showed smaller waist sizes if they followed the activity goals closely.

No safety concerns were reported. There were no serious adverse events or reasons for participants to stop using the tracker due to side effects. The study did not report specific adverse events or discontinuations related to the intervention. This suggests the approach was well tolerated by the participants over the one-year period.

People should not overreact to these findings. The study examined associations rather than proving that the tracker caused the weight loss. Other factors like diet and overall lifestyle likely played a role. The results apply to a specific group of overweight adults. This single study supports using wearable devices in long-term health programs but does not guarantee results for everyone. Patients should talk to their doctors before starting new health plans.

This research supports the use of wearable activity trackers in health programs. It suggests that consistent movement goals can help reduce body fat in some people. The findings are encouraging for those interested in using technology to support their health. However, the mixed results on waist size mean that not all body changes are guaranteed. Realistic expectations are important when using these tools for weight management.

What this means for you:
Wearable tracker use linked to lower body fat in overweight adults after one year.

Study Details

Study typeRct
Sample sizen = 502
EvidenceLevel 2
Follow-up12.0 mo
PublishedMay 2026
View Original Abstract ↓
BACKGROUND: Wearable activity trackers are commonly used in mHealth weight loss interventions, but evidence linking adherence to moderate-to-vigorous physical activity (MVPA) goals with changes in body composition is limited. We examined associations between adherence to study-prescribed MVPA goals and changes in percent body fat and sex-specific waist circumference (WC) over 12 months in the SMARTER trial. METHODS: Participants (N = 502, 79.5% female; mean age 45 years; mean BMI 33.7 kg/m) were randomized to self-monitoring of diet, PA, and weight (SM) or SM plus daily tailored feedback messages (SM + FB). Weekly adherence to ≥300 min/week of MVPA was quantified using Fitbit-derived equivalents. Associations between MVPA adherence and changes in percent body fat and sex-specific WC over 12 months were examined using linear mixed models. RESULTS: Among the full sample, greater MVPA adherence was associated with reductions in body fat (b = -0.01; 95% CI: -0.02, -0.005), but not in WC (women: b = -0.01; -0.03, 0.01; men: b = -0.03; -0.05, 0.0002). Among the completers, higher adherence was associated with decreases in body fat (b = -0.01; -0.02, -0.004) and WC (women: b = -0.02; -0.04, -0.004; men: b = -0.04; -0.08, -0.003). CONCLUSIONS: Higher MVPA adherence was associated with favorable changes in adiposity over 12 months, supporting the use of wearable-derived PA measures in long-term mHealth behavioral interventions.
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