Weight loss maintenance among truck drivers in the SHIFT randomised controlled trial, USA.

Objective: To evaluate weight loss maintenance among truck drivers following an effective initial intervention and to test a priori hypotheses that social support and stress factors would moderate long-term success.

Methods: Commercial truck drivers enrolled in the Safety & Health Involvement For Truckers cluster-randomised controlled trial (22 terminal clusters; n=452) completed measurements at baseline, postintervention (6 months) and 1 year postintervention (18 months) in the USA in 2012-2015. The mobile health intervention was a group-based competition involving self-monitoring, feedback, incentives, online training and motivational interviewing.

Results: In an intent-to-treat analysis, the difference between groups at 18 months post-baseline in mean body weight was -0.92 kg (p=0.328; intervention=0.00, control=+0.92). Moderation analyses revealed a significant between-group intervention effect on body weight at 18 months for drivers with supervisors who engaged in higher levels of family supportive supervisor behaviours (p=0.033; group difference=-2.74 kg). Intervention effects on several diet and exercise outcomes at 18 months were also significantly moderated by social support and stress factors. Within the intervention group, high initial programme participation was associated with significantly greater 18-month weight loss than lower participation (p<0.001; -3.43 kg vs +2.17 kg).

Conclusions: The intervention produced significant long-term weight loss for truck drivers with a supportive supervisor, providing further evidence for the broad health benefits of this workplace relationship. Additional findings highlight the value of initial programme participation and may inform future replications and extensions of similar health programmes for truck drivers.

Trial registration number: NCT02105571.