Eligible studies were randomised controlled trials (RCTs) that evaluated lifestyle interventions that aimed at reducing the incidence of diabetes in patients with impaired glucose tolerance. Trials had to report observation time of more than six months. The primary outcome of interest was incidence of diabetes. Various secondary outcomes such as all-cause mortality, diabetes mortality and quality-adjusted life-years (QALY) and clinical parameters were also of interest. Trials were excluded if they included patients with diabetes.
Lifestyle interventions included advice on healthy diet or diet modification and/or regular exercise. Some studies used face-to-face sessions and others used telephone contact. Control groups were described as using a standard intervention but the authors reported that some groups received minimal lifestyle interventions. Two trials included intervention arms that compared metformin to standard interventions (these results are not reported in this commentary). Mean ages of patients ranged between 45 and 55 years. Body mass index (BMI) varied between 24 and 34 kg/m². Where reported, 32% to 100% of the participants were men. Trials were conducted in India, Japan, Sweden, China, Netherlands, Finland and USA.
Two reviewers selected trials for inclusion blinded for author, journal and publication date.