Assessment of study quality
The authors did not state that they assessed validity.
Data extraction
All data were continuous. Mean changes from baseline (with standard errors) and percentage changes from baseline were reported. Where the standard error of the mean change was not reported in the primary study, the upper limit was estimated from the standard deviations of the before and after measures. For crossover or paired designs, the data for each phase were extracted separately, provided that baseline values for each phase were available.
The authors did not state how the data were extracted for the review, or how many reviewers performed the data extraction
Methods of synthesis
The data were pooled in inverse-variance meta-regression analysis, using hierarchical linear mixed models. The percentage reduction in the outcome was used as the dependent variable. Regression models controlled for correlation between observations within the same study and for differences between studies in the duration of the intervention. The restricted maximum likelihood method was used to estimate model parameters, and denominator degrees of freedom were calculated using the method of Berkey et al. (see Other Publications of Related Interest). Some clinical differences between the studies were investigated in single-covariate regression analyses. Further analyses were conducted to investigate the effect of weight change on glycaemia and lipid outcomes.