Abstract
Research on the conceptualization of adherence to treatment has not addressed a key question: Is adherence best defined as being a uni-dimensional or multi-dimensional behavioral construct? The primary aim of this study was to test which of these conceptual models best described adherence to a weight management program. This ancillary study was conducted as a part of the POUNDS LOST trial that tested the efficacy of four dietary macronutrient compositions for promoting weight loss. A sample of 811 overweight/obese adults was recruited across two clinical sites, and each participant was randomly assigned to one of four macronutrient prescriptions: (1) Low fat (20% of energy), average protein (15% of energy); (2) High fat (40%), average protein (15%); (3) Low fat (20%), high protein (25%); (4) High fat (40%), high protein (25%). Throughout the first 6 months of the study, a computer tracking system collected data on eight indicators of adherence. Computer tracking data from the initial 6 months of the intervention were analyzed using exploratory and confirmatory analyses. Two factors (accounting for 66% of the variance) were identified and confirmed: (1) behavioral adherence and (2) dietary adherence. Behavioral adherence did not differ across the four interventions, but prescription of a high fat diet (vs. a low fat diet) was found to be associated with higher levels of dietary adherence. The findings of this study indicated that adherence to a weight management program was best conceptualized as being multi-dimensional, with two dimensions: behavioral and dietary adherence.
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Notes
Most contemporary authors have preferred the term “adherence” over the term “compliance,” since the former term connotes behavior of the patient/participant related to following a medical prescription whereas the latter term connotes following a dictum from a higher authority. We concur with this contemporary preference for the term adherence and that will be our choice of wording throughout the paper.
The primary aim of the POUNDS LOST trial was to test the efficacy of four different macronutrient prescriptions for weight loss and health outcomes. The study design intentionally de-emphasized changes in physical activity and exercise so that diet effects on weight and health changes would not be overshadowed by changes in physical activity. Using this rationale, physical activity goals were set quite low, i.e., only 90 min per week of exercise via walking, and explicit instructions to promote physical activity, exercise, or fitness were deliberately avoided throughout the intervention. The study design called for equivalent levels of physical activity and other behavioral changes (e.g., self-monitoring and attendance to sessions, across the four treatment arms). As noted by Sacks et al. (2009), these objectives were met. One consequence of this decision for this ancillary study was that data collection related to adherence to physical activity prescriptions was not a part of the study design. As noted later in the paper, one effect of a lack of focus on physical activity was that participants did not report minutes of exercise nearly as often as they reported food intake (see Table 4).
The average number of extra sessions during the first 6 months of the study was 0.16 sessions. Participants assigned to the moderate fat/high protein diet attended more extra sessions (M = 0.31 vs. means ranging from 0.06 to 0.15 for the other treatment arms). This difference (p < 0.02) did not influence the findings since extra sessions were not counted toward adherence to attendance goals.
The use of absolute values based upon actual (not percent) deviations from caloric and macronutrient goals had the effect of creating dietary adherence variables that were not dependent upon one another, which would occur if percentages or raw (positive and negative deviations) values were used in the factor analyses.
We were concerned that these two factors may have emerged because of difference in variance that could be attributed to different methods. For example, the dietary factor was derived from indicators that were calculated by the computer tracking system and the behavioral factor included data that had been entered by counselors (for attendance) and self-monitoring by the participants. We converted the data for all eight variables to standardized scores and obtained identical findings. This statistical control may not entirely rule out this possible explanation of the factor structure; therefore, we believe that it will be important for future studies to evaluate the dimensionality of adherence to using entirely different methods for data collection and summary.
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Acknowledgments
Supported by a cooperative agreement award HL073286 from National Heart, Lung, and Blood Institute, National Institutes of Health; and NIH General Clinical Research Center grant RR-02635. This study was approved by the appropriate ethics committees and was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. All persons gave their informed consent prior to their inclusion in the study.
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Williamson, D.A., Anton, S.D., Han, H. et al. Adherence is a multi-dimensional construct in the POUNDS LOST trial. J Behav Med 33, 35–46 (2010). https://doi.org/10.1007/s10865-009-9230-7
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DOI: https://doi.org/10.1007/s10865-009-9230-7