Six RCTs with a total of 487 participants were included in the review; 249 patients were randomised to the PMR group and 238 to the RCD group. The duration of the included studies ranged from 3 to 51 months, with the majority of studies lasting 12 months. Due to the nature of the interventions, blinding of the patients was not possible in any of the studies.
All of the studies achieved a moderate quality assessment rating.
Weight loss at 3 months.
Each individual study showed a statistically significant weight loss at 3 months in both the PMR and RCD groups (P<0.001). Whilst each study reported greater weight loss in the PMR group than the RCD group, this was only statistically significant in 3 studies. However, when the studies were combined using summary data and using IPD, the difference in weight loss between the PMR and RCD groups was statistically significant.
Based on the fixed-effect meta-analysis, the random-effects meta-analysis and the pooling of IPD from participants who completed 3 months of the studies, the PMR group lost between 6.19 and 6.5 kg and the RCD group lost between 3.34 and 3.96 kg. The weight loss in the PMR group was 2.54 to 3.01 kg more than that in the RCD group.
The authors stated that when using Hedges and Olkin's Q statistic, there was significant heterogeneity between studies for the estimates of weight loss and the effectiveness of the PMR programme. Heterogeneity was also statistically significant when testing the significance of interactions between study and group effects.
Data pooled using the LOCF and MI methods for missing imputations produced the same results as the completer analysis.
At 3 months, 34% of the participants in the RCD group and 72% of the participants in the PMR group had lost 5% or more of their initial body weight. The difference was statistically significant.
The drop-out rate between the PMR and RCD groups was not statistically significantly different at 3 months: 16% and 19%, respectively. None of the participants who dropped out reported any programme- or product-related adverse events.
Weight loss at one year.
Four studies for the RCD and five for the PMR groups reported one year follow-up data. Three of the 4 studies reported statistically significant weight loss in the RCD group, while four of the 5 studies reported statistically significant weight loss in the PMR group. Three of 4 studies reported greater weight loss in the PMR group than the RCD group; this was statistically significant in 2 studies.
When summary data were combined using a fixed-effect model, and when IPD were pooled, the difference in weight loss between the PMR group and the RCD group was statistically significant. However, when combining summary data using the random-effects model, the difference was not statistically significant (P=0.142).
Based on the fixed-effect meta-analysis, the random-effects meta-analysis and the pooling of IPD from participants who completed one year of the studies, the PMR group lost between 6.97 and 7.31 kg and the RCD group lost between 2.61 and 4.35 kg. The weight loss in the PMR group was 2.43 to 3.39 kg more than that in the RCD group.
The authors stated that when using Hedges and Olkin's Q statistic, there was significant heterogeneity between studies for the estimates of weight loss and the effectiveness of the PMR programme. Heterogeneity was also statistically significant when testing the significance of interactions between study and group effects.
Data pooled using the LOCF method for missing imputations produced the same results as the completer analysis. However, when using the MI method, the statistical significance of the difference in weight loss between the PMR and RCD groups was 0.119.
At one year, 33% of the participants in the RCD group and 74% of the participants in the PMR group had lost 5% or more of their initial body weight.
The drop-out rate was statistically significantly higher in the RCD group than in the PMR group at one year: 64% and 47%, respectively. None of the participants who dropped out reported any programme- or product-related adverse events.
Biomarker analyses.
At both 3 months and one year, all eight of the risk factors improved and were positively associated with their baseline values (P<0.001). Improvements in glucose, triglyceride, low-density lipoprotein cholesterol and systolic blood-pressure were statistically, significantly positively associated with weight loss after 3 months. There was a statistically significant additional effect of PMR on improvements in plasma insulin levels after 3 months and one year. Total cholesterol was statistically, significantly, positively associated with weight loss at one year, in addition to glucose, triglyceride, low-density lipoprotein cholesterol and systolic blood-pressure.
Results of analysis stratified by diabetes status.
The weight loss of diabetic participants was lower at one year than at 3 months for both the RCD group (1.74 kg at one year versus 4.88 kg at 3 months) and the PMR group (4.5 kg at one year versus 7.34 kg at 3 months). However, nondiabetic patients had lost more weight at one year than at 3 months in both groups.
At one year, 77% of diabetic participants had dropped out of the RCD group and 79% out of the PMR group, compared with 60% and 35% of nondiabetic participants, respectively.
Publication bias.
Kendall's tau correlation did not support publication bias, except for weight loss at one year in the RCD group.
The authors also presented narrative results of 2 studies, identified during the course of their study, which evaluated a PMR programme. Both studies found that participants in the PMR groups lost more weight than participants in the control groups at 12 weeks; this result was statistically significant in one study.