Ninety-eight studies met the inclusion criteria: 23 studies rated as high quality (n=3,600) were included for further analyses and 51 moderate and 24 weak studies were excluded from the analyses. All 23 studies included in the analysis reportedly were randomised; only 22.7% described the methods of randomisation. Only 17.49% of studies reported calculating sample size, 30.4% blinded outcome assessors and 27.3% used intention-to-treat analysis. Dropout rates were high in most studies; there were no significant differences in baseline variables between dropouts and those who completed the studies.
The studies that assessed dietary and exercise interventions found that at six months diet alone or diet plus exercise interventions group had lost statistically significantly more weight than exercise alone. Two studies used the Internet to deliver the programme and reported statistically significant weight loss at six and 12 months compared to the control group.
Three of four studies that evaluated exercise interventions alone achieved weight loss in the intervention group compared to the control group. The fourth study, in which participants engaged in high physical activity, led to much more weight loss at the end of the programme compared to the control group. Of those who maintained their level of exercise, weight loss was still significant at one year after the intervention.
For dietary reduction interventions alone, only two studies that used high-protein, low-fat diet were successful in achieving weight reduction in the short-term and there was no difference between intervention and control groups after six months. The remaining five studies did not show an effect of the intervention.