Background: Designing a health promotion program to increase physical activity may contribute to weight management. The purpose of this study was to investigate a theory of planned behavior (TPB) program to address this problem in military people.

Methods: Eighty-four obese/overweight military personnel were randomised into the intervention or control group. A questionnaire assessed demographics, aspects of the TPB program, and physical activity levels. Also assessed were blood glucose and lipid levels. The intervention consisted of seven educational sessions based on TPB. Data were collected at baseline and 3 months after the intervention.

Results: All constructs of the TPB improved between baseline and follow-up in the intervention group (p <.001), while there were no significant changes in the control group (within-group comparisons). Between-group comparisons on TPB measures revealed differences in all domains when results were controlled for baseline covariates. Greater light and moderate physical activity was observed in the intervention group. Body mass index decreased significantly within the intervention group (p <.001). Changes in triglyceride and high-density lipoprotein also favored the intervention over the control group.

Conclusion: An intervention based on the TPB may be effective in promoting physical activity and decreasing weight in military personnel who are obese or overweight.