The comparative and cumulative effects of a dietary restriction and exercise on weight loss

Objective: To assess the independence of changes made in diet and physical activity for weight loss; and, to examine the comparative and cumulative effects of these behavioral changes on weight loss outcomes. Design: The observational study is based on longitudinal data collected from 674 women and 288 men enrolled in a 2-year weight loss program introduced into a managed care setting. Measurements: The outcome variable was body mass index (BMI) change from baseline to 2-year follow-up. Primary independent variables were changes in physical activity and dietary fat intake, assessed as continuous measures using the Paffenbarger Physical Activity Questionnaire and Block Fat Screener Questionnaire, respectively. Two-way ANCOVA was used to assess the relative effect on BMI of behavioral changes. Results: Study results showed no preference for diet or physical activity change as a weight loss strategy. For both genders, the relationship between the two behaviors was synergistic rather than compensatory. Examination of the comparative benefits of behavioral changes indicated that, for women and men, restricting fat intake was more effective than increasing exercise for weight loss. While fat restrictions alone contributed to weight loss in both genders, exercise alone provided weight loss benefits to men, only. The cumulative effect of weight loss behaviors varied by gender. In women, an interaction was observed. The response of weight to fat restriction was greater among those who increased their exercise moderately or substantially. In men, there was no interaction; exercise increases helped to offset weight gain or provided small weight loss benefits at all levels of dietary fat change. Conclusion: Dietary changes appeared to be more effective than increased physical activity for weight loss. For women, the cumulative effect of concomitant changes in diet and exercise on weight loss was more than additive.