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Psychosocial Predictors of Weight Outcomes in the PREMIER Trial
Phillip J. Brantley, Ph.D.
Pennington Biomedical Research Center
Agenda and Abstracts
PREMIER was a multiple site, randomized clinical trial that examined two lifestyle interventions on blood pressure (BP) relative to an advice only condition. Weight loss was a secondary outcome of the trial. Both of the lifestyle interventions included “established” interventions that implemented the 1993 recommendations of the Joint National Committee on the Detection, Evaluation, and Treatment of High Blood Pressure (JNC V, 1993). Specifically, recommendations were to 1) lose weight if overweight, 2) reduce sodium intake, 3) limit alcohol consumption, and 4) increase physical activity. In addition to the established recommendations, one intervention condition, “established plus DASH”, included the dietary patterns based on the Dietary Approaches to Stop Hypertension (DASH) clinical trial (Appel et al., 1997). These dietary recommendations included increased fruit and vegetable consumption, low fat dairy products, reduced saturated and total fat, and reduced cholesterol intake.
Participants included 810 adults who were 25 years and older (average of 50 years) with above optimal BP including individuals with stage 1 hypertension who were yet to be prescribed antihypertensive medications. Eligibility criteria included a systolic BP of 120-159 mmHg and diastolic BP of 80-95 mmHg, and BMI between 18.5-45 kg/m2. Persons with diabetes using insulin or oral hypoglycemic medications were excluded, as well as persons who had experienced a significant cardiovascular event. The average BMI was 33 (95% were overweight). The sample was composed of 62% women and 34% African Americans.
Measures in addition to BP and weight included psychosocial questionnaires designed to measure constructs hypothesized to be mediators, modifiers or outcomes of the intervention effect. For the purposes of this presentation, these psychosocial measures were examined as potential predictors of weight outcomes. Social cognitive theory suggests that healthy lifestyle behavioral change is the result of reciprocal relationships among the environment, personal factors, and behavior. Self-efficacy is one of the most important characteristics that can determine behavioral change. Self-efficacy was measured using both the Eating Habits Confidence Survey and the Exercise Confidence Survey (Sallis et al., 1988). Social support was measured using the Social Support and Eating Habits Survey and the Social Support and Exercise Survey (Sallis et al., 1987). These measures generated both a Family and Friends subscale score. Additional psychosocial constructs that were assessed as possible predictors of weight change were: Quality of Life, Perceived Stress, and Perceived Body Image. Quality of life was measured using the Medical Outcomes Study Short Form (MOS SF-36; Ware, 1993). The domains of the SF-36 were grouped into two global scales: physical and mental health. Perceived stress was measured using the Perceived Stress Scale (PSS; Cohen 1983), and perceived body image was measured using the Stunkard silhouettes (Stunkard, 1983). Higher difference scores between current and ideal body image on the silhouettes represented higher levels of body dissatisfaction.
Procedures for intervention groups (established and established plus DASH) consisted of frequent participant contacts to promote weight loss, i.e. weekly for first 3 months and bimonthly for another 3 months. Monthly contacts from 6 to 18 months encouraged continued weight loss or weight loss maintenance.
Results were based on repeated measures multiple regression analyses to determine whether psychosocial measures taken at baseline and at 6 months could predict repeated measures of weight at baseline, 6, 12 and 18 months. All analyses were conducted with participants in the two intervention groups combined (n=537). Greater weight loss appeared to be associated with higher baseline scores of perceived stress and higher ratings of physical quality of life (SF-36). Weight loss also tended to be greater in individuals who reported less baseline family social support for healthy eating and less dissatisfaction with their perceived body image. African Americans in PREMIER lost less weight than non-African Americans. A significant interaction effect suggested that among non-African American participants but not African Americans, those who reported more support for exercise by their friends reported more weight loss. Results of the repeated measures multiple regression examining psychosocial predictors (taken at 6 months, i.e., the end of intensive treatment) revealed that weight loss was associated with higher ratings of physical quality of life and more confidence in one’s ability to follow a healthy diet. Participants who were more successful at weight loss reported less social support by their family for healthy eating and less dissatisfaction with their perceived body image. Finally a logistic regression analysis examined two groups of intervention participants, those who had gained more than 3 kilograms after initial treatment (relapse group) versus those who have not gained 3 kilograms during the months following intensive treatment (maintainers). None of the psychosocial measures taken at baseline or 6 months emerged as significant predictors, however it should be noted that 90 percent of the participants remaining at follow-up were classified as maintainers.
Conclusion. Although these preliminary analyses may not represent the best or final model to account for predictors of weight outcomes in PREMIER participants, they do suggest that weight loss appears more likely in individuals who view themselves as physically healthy and who appear to be relatively satisfied with their body image.
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