This study examined the individual and combined effects of dietary weight loss and/or aerobic exercise interventions on HRQOL among sedentary, overweight/obese postmenopausal women. To our knowledge, this trial is the first to compare individual and combined effects of dietary weight loss and exercise intervention on HRQOL in overweight/obese, postmenopausal women without major medical conditions. We found that the combined dietary weight loss and exercise group improved more aspects of HRQOL and psychosocial factors (depression, stress and social support) with larger increments compared with diet or exercise alone. We also found significant associations between weight loss, increased aerobic fitness, and improvements in HRQOL and psychological factors, suggesting that these factors may explain, at least in part, the improved HRQOL observed in the diet and exercise interventions.
The combined dietary weight loss and exercise group improved more aspects of HRQOL and with larger increments compared with diet or exercise alone. Our findings were consistent with previous trials in clinical populations, among those with type 2 diabetes  or osteoarthritis . The latter trial reported up to a 16.5 point increase in all subscales of SF-36 with a 18-month diet+exercise intervention , which was greater than the observed changes in our sample (5-11 points). This may be caused by differences in the study sample, as the observed increase in HRQOL scores among our combined diet+exercise group was consistent with previous weight loss trials in general populations [4, 17]. In a 6-month weight loss trial (low calorie diet and aerobic exercise) among 298 obese women (age 50-75), women lost 9.4% of baseline weight and increased physical functioning and vitality scores by 6 and 8 points, respectively . Another 6-month weight loss trial in 144 overweight/obese adults reported a mean weight loss of 5.6 kg and 2 to 11-point improvements in 8 subscales of SF-36 .
In contrast to a number of studies reporting positive effects of exercise on HRQOL, we did not find significant improvements in any aspects of HRQOL in women randomized to the exercise-only group. It is possible that our participants had high baseline HRQOL which could have caused a ceiling effect. Preference for type of exercise could also have affected the results. Courneya et al. found that participants who preferred resistant training showed greater increase in HRQOL when assigned to resistant training group compared with those assigned to aerobic exercise or control groups . Our participants might have preferred to be assigned to a group other than the exercise-only group, which could have resulted in minimal changes in HRQOL.
The combined diet+exercise intervention also improved psychosocial factors (depression, stress, and social support), while there were no effects on these factors in the diet or exercise alone groups. Although we are not aware of studies comparing these psychological outcomes in individual vs. combined diet and exercise interventions, lifestyle modification programs involving diet and exercise have been shown to improve psychological health. A 12-month intensive lifestyle intervention program of the Look AHEAD (Action for Health in Diabetes) Trial, mediated through weight loss (mean 8.8 kg weight loss among intervention group) and aerobic fitness, improved depression in 4223 overweight adults with type 2 diabetes . A cardiac rehabilitation program reduced stress, which was associated with weight loss and improved aerobic fitness . Our finding that the combined diet+exercise group improved psychological factors is consistent with these studies, but the reasons for the improvements are not clear. We did not find any significant correlations between weight loss or aerobic fitness with these psychosocial factors except for a correlation between weight loss and reduced depression. Future studies are recommended to investigate mechanisms by which lifestyle interventions may improve psychological health.
Positive changes in depression and stress were significantly associated with 4 subscales of HRQOL, which remained significant after adjusting for changes in weight and aerobic fitness. Studies have shown that psychological disorders affect various aspects of HRQOL. An analysis of 11,242 outpatients in the U.S. showed that individuals who are depressed have lower physical functioning, role-physical and social functioning compared with non-depressed individuals . Another study has shown that increased depressive symptoms were associated with decline in all 8 aspects of SF-36 among female patients with remitted major depression disorder . Our study confirmed that psychological conditions have a significant impact on HRQOL and that a lifestyle behavioral change of a diet and exercise in combination, is a potential method to improve psychological health.
Improved aerobic fitness was an independent predictor of 12-month changes in physical functioning. Consistent with our findings, Ross et al. found that changes in BMI and aerobic fitness independently explained a change in physical functioning score, and that improved aerobic fitness had independent effects beyond BMI change only in physical functioning scale among 8 subscales of SF-36 in a 6-month lifestyle intervention among obese women . An analysis from the Look AHEAD trial found that both weight loss and increased aerobic fitness mediated the intervention effects on physical composite scores . In our previous 12-month exercise trial in 173 postmenopausal women, we found that a change in aerobic fitness was associated with a change in physical functioning but not with changes in either mental health or general health .
Weight loss in the present study was associated with improvements in both physical and mental aspects of HRQOL. A 12-month follow-up of a 6-month lifestyle intervention found that individuals who continued to lose weight during the follow-up period showed improved vitality and general health of SF-36 and that weight loss was associated with improvements in these aspects of SF-36 among 508 postmenopausal women . Our findings confirmed that obesity is a risk factor for reduced HRQOL and that weight loss can improve both physical and mental aspects of HRQOL.
Previous studies have shown an important role of psychosocial factors on explaining how exercise impacts quality of life [38–41]. In multiple sclerosis patients, depression, social support, self-efficacy and fatigue mediated effects of exercise on quality of life . Greater social support was associated with stronger exercise self-efficacy in older adults in another study . Exercise self-efficacy mediated the exercise effect on mental and physical aspects of HRQOL in older women . Higher exercise self-efficacy was associated with greater physical power score, a combined score of aerobic fitness and five items from the Senior Fitness Test  among older adults . It is possible that the observed associations of weight loss and improved aerobic fitness with HRQOL in our study could be mediated through increase in exercise self-efficacy. Future studies may benefit from testing psychosocial predictors of quality of life including self-efficacy to further determine the mechanism of how interventions affect HRQOL.
The strengths of this trial include its large sample size; randomized controlled design; three intervention arms allowing direct comparisons of individual and combined exercise and diet groups to each other and controls; excellent adherence to intervention prescription; low rate of drop-outs (9%); and use of validated measures of HRQOL and psychosocial factors. In particular, direct comparison between combined diet+exercise and diet or exercise alone allowed us to understand the individual and combined contribution of these lifestyle behaviors on HRQOL.
This study is limited by some factors that should be kept in mind when interpreting the results. Our sample consisted primarily of non-Hispanic White women with a high education level on average. Hence, our findings may not be generalizable to men, or women in other ethnic groups or with different education levels. Another limitation is the relatively high HRQOL scores among our sample. Even though we found significant effects on several aspects of HRQOL, the analysis may have suffered from a ceiling effect. Based on these limitations, future studies are needed to test the effects of these dietary weight loss and exercise interventions in other populations such as women of other race/ethnicity groups or in men.