Explaining the effects of a 1-year intervention promoting a low fat diet in adolescent girls: a mediation analysis
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Explaining the effects of a 1-year intervention promoting a low fat diet in adolescent girls: a mediation analysis Leen Haerens*1, Ester Cerin2, Benedicte Deforche1, Lea Maes3 and Ilse De Bourdeaudhuij1 Address: 1Ghent University, Department of Movement and Sports Sciences, Watersportlaan 2, Gent, 9000, Belgium, 2University of Hong Kong, Institute of Human Performance, 111 Pokfulam Road, Pokfulam, Hong Kong and 3Ghent University, Department of Public Health, De Pintelaan 185, BLOK A, Gent, 9000, Belgium Email: Leen Haerens* - [email protected]; Ester Cerin - [email protected]; Benedicte Deforche - [email protected]; Lea Maes - [email protected]; Ilse De Bourdeaudhuij - [email protected] * Corresponding author
Published: 9 November 2007 International Journal of Behavioral Nutrition and Physical Activity 2007, 4:55 5868-4-55
doi:10.1186/1479-
Received: 27 October 2006 Accepted: 9 November 2007
This article is available from: http://www.ijbnpa.org/content/4/1/55 © 2007 Haerens et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Background: Although it is important to investigate how interventions work, no formal mediation analyses have been conducted to explain behavioral outcomes in school-based fat intake interventions in adolescents. The aim of the present study was to examine mediation effects of changes in psychosocial determinants of dietary fat intake (attitude, social support, self-efficacy, perceived benefits and barriers) on changes in fat intake in adolescent girls. Methods: Data from a 1-year prospective intervention study were used. A random sample of 804 adolescent girls was included in the study. Girls in the intervention group (n = 415) were exposed to a multi-component school-based intervention program, combining environmental changes with a computer tailored fat intake intervention and parental support. Fat intake and psychosocial determinants of fat intake were measured with validated self-administered questionnaires. To assess mediating effects, a product-ofcoefficient test, appropriate for cluster randomized controlled trials, was used. Results: None of the examined psychosocial factors showed a reliable mediating effect on changes in fat intake. The single-mediator model revealed a statistically significant suppression effect of perceived barriers on changes in fat intake (p = 0.011). In the multiple-mediator model, this effect was no longer significant, which was most likely due to changes in perceived barriers being moderately related to changes in self-efficacy (-0.30) and attitude (-0.25). The overall mediated-suppressed effect of the examined psychosocial factors was virtually zero (total mediated effect = 0.001; SE = 7.22; p = 0.992). Conclusion: Given the la
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