Healthy intentions: A daily diary intervention study on physical activity and unhealthy snacking at work.

The intervention successfully improved employees' accelerometer-assessed physical activity during the 2-week study phase at the between-person level.

• Study employed a randomized controlled design within a daily diary study with 73 employees over 516 days
• The intervention was based on mental contrasting with implementation intentions (MCII)
• Physical activity was objectively assessed via accelerometer
• The intervention effect was detected at the between-person level of analysis

Participants in the daily-choice intervention group were more physically active than participants in the daily-assignment intervention group.

• Two intervention groups were compared: a daily-assignment group (refresher focused on a pre-assigned behavior each day) versus a daily-choice group (participants chose which behavior to focus on each day)
• The daily-choice group showed higher levels of accelerometer-assessed physical activity than the daily-assignment group
• This suggests that allowing behavioral autonomy in daily intervention refreshers confers additional benefit for physical activity

Within-person results did not provide evidence of an additional benefit from daily intervention refreshers.

• The study examined whether day-level intervention refreshers produced additional within-person variation in health behaviors
• No significant within-person benefit of daily refreshers was found for either physical activity or unhealthy snacking
• This suggests the primary intervention effect operated at the between-person rather than within-person level

The intervention was ineffective at reducing unhealthy snacking at work.

• Unhealthy snacking during the workday was a primary target behavior of the intervention alongside physical activity
• Despite the MCII-based intervention design, no significant reduction in unhealthy snacking was observed
• This null finding applied across the overall intervention comparison with the passive control group

Exploratory analyses suggested the intervention was more effective in work environments characterized by higher levels of job stressors for both physical activity and unhealthy snacking.

• Job stressors in the work environment moderated intervention effectiveness
• Higher job stressor levels were associated with greater intervention benefit for both target behaviors
• These moderating effects were identified through exploratory (not pre-specified) analyses
• Work context is highlighted as a boundary condition for intervention effectiveness

Exploratory analyses suggested the intervention was more effective among individuals with higher baseline levels of unhealthy snacking.

• Baseline unhealthy snacking level moderated the intervention's effect on snacking outcomes
• Individuals who engaged in more unhealthy snacking at baseline showed greater benefit from the intervention
• This was identified as an individual-level boundary condition for intervention effectiveness
• These findings were characterized as exploratory

The study design compared an individual-level MCII intervention against a passive control group using a randomized controlled daily diary methodology.

• 73 employees participated across 516 days of diary data
• Three groups were included: passive control, daily-assignment intervention, and daily-choice intervention
• The study phase lasted 2 weeks
• Both between-person and within-person levels of analysis were employed