Five RCTs (11 group comparisons) were included in the review (n at least 376 participants; where reported, range was 49 to 160). No trials reported allocation concealment or blinding of participants. One study reported blinding of assessors. One study used an intention-to-treat analysis. All trials reported the number of withdrawals; reasons for withdrawals were described in only two. Attrition rates ranged from 3.4% to 64%. Follow-up ranged from 52 to 119 weeks.
Group-based treatment was associated with a significant weight loss at one year compared with individual treatment (WMD -1.4kg, 95% CI -2.7kg to -0.1kg; 11 groups). Greater weight loss at one year was achieved for group-based interventions compared to individual interventions when trials offered a financial reward (WMD -2.8 kg, 95% CI -5.4kg to -0.2kg; five groups) and where treatment was psychologist-led (WMD -3.1kg, 95% CI -5.5kg to -0.6kg, number of groups not reported). There was no significant difference in weight loss between group- and individual-based treatment, where there was no financial reward (six groups) or where the treatment was dietician-led. No further subgroup analyses were conducted due to insufficient data.
I2 and number of comparison groups for healthcare professional subgroup analyses were not reported. In all other analyses, there was no evidence of statistical heterogeneity.