Objective To evaluate the effectiveness of a draft occupational health practice guideline aimed at preventing weight gain on employees' physical activity, sedentary behaviour and dietary behaviour and on body weight-related outcomes.

Methods A randomised controlled trial was performed comparing guideline-based care to usual care among 16 occupational physicians and 523 employees in the Netherlands between 2009 and 2011. Occupational physicians in the intervention group followed the draft guideline by providing advice to employers on how to assess and intervene on the obesogenic work environment and conducted five face-to-face behavioural change counselling sessions with employees to improve their lifestyle. Data of employees were collected by questionnaire and physical measurements at baseline and 6-months follow-up. Linear and logistic regression analyses were performed to determine effects.

Results The intervention showed significant effects on sedentary behaviour at work (β −28 min/day, 95% CI −2 to −54) and on fruit intake (β 2.1 pieces/week; 95% CI 0.6 to 3.6). No significant intervention effects were found for physical activity, sedentary behaviour in leisure time or during weekend days, snack intake and body weight-related outcomes.

Conclusion Guideline-based care resulted in a more favourable sedentary behaviour at work and increased fruit intake but did not improve employees' physical activity, snack intake or body weight-related outcomes.

Trial registration number ISRCTN/73545254 and NTR/1190.