Abstract
Objective To develop and evaluate the long-term effectiveness of an intervention program, based on preaction-stage–oriented change processes of the Transtheoretical Model of Behavior Change, that could be delivered in a group setting to help participants lower dietary fat intake.
Design An enhanced version of the nonequivalent control group experimental design was used. Entire sections of an undergraduate introductory nutrition science course were assigned to an experimental, pretest/posttest control, or posttest-only control group. Daily fat intake and stage of change of the experimental and pretest/posttest control groups were determined at the pretest and posttest and 1-year later at a follow-up test. Every 1 to 2 weeks during the study, stage of change of the experimental group was assessed. Daily fat intake of the experimental group was assessed at study midpoint. Daily fat intake and stage of change of the posttest-only control group was determined at the posttest. Pretest results were used to place participants of the experimental and pretest/posttest control groups in either the preaction stage (ie, precontemplation, contemplation, or preparation) or the action/maintenance stage.
Subjects/setting The sample consisted of 38, 30, and 42 undergraduate students who were assigned to the experimental, pretest/posttest control, and posttest-only control groups, respectively.
Intervention The experimental group participated in a group-based, dietary fat intake intervention that included a series of 11 lessons taught over a 14-week period. Each lesson was based on 1 or 2 of the preaction-stage–oriented change processes of the Transtheoretical Model.
Main outcome measures Data were evaluated to determine the effects of the intervention program on long-term dietary fat reduction and stage of change progression.
Statistical analysis performed Analysis of variance, repeated-measures analysis of variance, and paired
t tests.
Results For pretest and posttest dietary fat intake scores, stage and time were significant, and there was a significant time-by-stage interaction. Time was significant for pretest and posttest stage scores. Subjects in the preaction-stage experimental group significantly increased their mean stage of change and reduced their fat intake between the pretest and posttest; these changes persisted for 1 year. Pretest/posttest control group participants who began in a preaction stage also significantly increased their mean stage and reduced fat intake by the posttest, but these changes did not endure until the follow-up test.
Applications/conclusions This intervention program produced an enduring, significant reduction in mean dietary fat consumption and a significant progression in mean stage of change of subjects in the experimental group who were in the preaction stage. It may be appropriate to design group interventions to use preaction stage processes rather than the more traditionally used action and maintenance stages change processes.
J Am Diet Assoc. 2000;100:335-342.