The findings of this study support the hypothesis that participation in an intensive lifestyle behavior modification intervention for weight management was associated with significant improvement in HRQOL (relative to the control group), as measured by the PCS score of the SF-36 and the BDI-II. Assignment to ILI was associated with significant improvements in PCS and BDI-II scores, whereas assignment to DSE was associated with worsening in PCS. The overall treatment effect on PCS (0.39) was greater than the relatively small effect size (0.13) that was observed for BDI-II, but was not sufficiently large to be considered clinically significant.24,25
The study also found that individuals with worse HRQOL at baseline derived the greatest benefits from the weight management intervention. Similar results were reported in an uncontrolled study26
of changes in HRQOL following pharmacologic and lifestyle treatment for obesity. This observation is consistent with statistical phenomenon called “regression to the mean”. It is noteworthy (see ) that for all three measures of HRQOL, the greatest benefits of ILI were observed for participants with baseline SF-36 scores indicative of poor HRQOL and baseline BDI-II scores indicative of mild to moderate depression‡
. We also tested for moderation of treatment effects by baseline BMI, baseline levels of pain complaints, disease severity, severity of baseline comorbid conditions, age, gender, and race. Baseline BMI, moderated the differential effects of the two treatment arms on PCS, but did not moderate the effects on MCS or BDI-II scores.
This study is one of the first to evaluate the potential mediation of treatment effects on HRQOL. We tested three putative mediators:21
changes in weight, fitness, and physical complaints. Mediation analyses (see ) indicated that the improvement in PCS associated with participation in the ILI arm was only partially mediated by the improvements in body weight, physical fitness, and reductions in physical complaints. Treatment effects related to BDI-II scores were partially mediated by changes in fitness and physical complaints and completely mediated by changes in body weight. The finding that changes in body weight, physical fitness, and physical complaints accounted for only a portion of the changes in PCS attributed to treatment suggests that other factors (e.g., counseling and group support, changes in the social and/or family environment, improved metabolic parameters, or improved functional abilities) may be critical variables that account for improved HRQOL that occurs with successful lifestyle modification related to weight management in overweight/obese adults diagnosed with type 2 diabetes.
These results significantly inform the medical professions about changes in HRQOL and lifestyle behavior change related to weight management. The research literature on this topic has yielded conflicting findings.15
This study addresses some of the primary shortcomings of previous studies:15
1) loss to follow-up for this study was quite low (2.9% for ILI and 4.3% for DSE) relative to earlier studies, 2) the sample size was large; 3) study assessors were blind to treatment assignment; 4) mediation of changes in HRQOL by changes in body weight, fitness, and physical complaints was tested; and 5) statistical analyses were adjusted for multiple comparisons.
The results suggest that the strongest effects of lifestyle modification were on HRQOL related to physical health. Furthermore, the largest changes in HRQOL were observed for participants with poorest quality of life at baseline. In this context, it is not surprising that the smaller-scale and less well-controlled investigations have yielded conflicting results pertaining to the effect of lifestyle weight management programs on HRQOL.15
Given the initial positive findings of the impact of participation in a lifestyle behavior modification program for obesity on HRQOL, it will be very important to observe the stability of improvement in HRQOL over longer periods of time. It is highly probable that a substantial portion of the participants in the ILI arm will regain some weight over the 11-year duration of the Look AHEAD trial.20
Only one uncontrolled study26
has reported on changes in HRQOL associated with weight regain, and this paper reported deterioration of improvements in HRQOL following weight regain.
The primary limitations of the study are the relatively brief duration of the study (i.e., 1 year) and the focus upon a highly selected population of overweight/obese adults who had been diagnosed with type 2 diabetes. These findings should not be generalized to other (less highly selected) populations and future reports on this sample are needed to determine if these changes in HRQOL persist over much longer periods of time.
In summary, participation in a 1-year ILI for weight loss improved HRQOL in overweight/obese adult type 2 diabetic participants. The greatest effects were observed for improvements in HRQOL related to physical functioning. For all three indicators of HRQOL, participants with the lowest quality of life at baseline derived the greatest HRQOL benefit from participation in the ILI. Improvement in HRQOL for physical health (PCS) was partially mediated by weight loss, improved fitness, and reductions in complaints related to physical problems. It is likely that other factors may account for additional variance in the beneficial changes in HRQOL associated with participation in a weight management program.