Eligible for inclusion in the review were interventions that were either replications or modifications of all or some components of the US Diabetes Prevention Program (DPP), Finnish Diabetes Prevention Study (DPS) or any other reference trial, or those including the reduction of diabetes risk or diabetes incidence explicitly. Eligible study designs were RCTs, before-and-after studies, cohort studies with or without a control group, and interrupted-time-series analyses. Eligible studies had to last least three months, with three months follow-up of single (either nutrition or physical activity programmes with or without medication) or combined (nutrition and physical activity) programmes, with or without medication. Eligible participants were adults with impaired glucose regulation at risk of diabetes. Comparators included no intervention or alternative intervention (single or combined).
Eligible studies had to be performed in routine clinical settings, be delivered on-site or in associated facilities, with outcome measures assessed on-site by general medical practitioners, specialist physicians, practice nurses, allied health professionals, community health staff or research staff attached to the service. Study authors were contacted to verify the study setting. Studies that included patients diagnosed with diabetes were only included in the review if outcomes were reported separately from patients without diabetes. Studies of diabetes education materials only, or medication only were excluded. Further details were given in the paper.
Studies had to report at least one of the following outcomes: improvement in objectively measured risk factors, such as weight loss or waist circumference reduction; metabolic outcomes indicative of diabetes reduction; self-reported or objectively measured behavioural outcomes. The secondary outcome was prevention of diabetes (incidence percentage or delay in onset or reduction in incidence over a given follow-up time).
All the included studies were performed in developed countries. Three studies were conducted in the UK. The age of the target population varied between studies, but half of the studies targeted middle-aged people only. Most studies included normoglycaemic partcipants. All interventions combined physical activity and dietary advice, with two studies additionally including medication. Half the physical activity interventions were structured. For group based interventions, the median number of sessions was six; for individual based interventions, the median number of sessions was 13.5. Most of the studies were delivered in specialist service or hospital outpatient clinics, or in general practitioners consulting rooms or community health centres. Nurses or allied health-care professionals usually delivered the interventions. Approximately 60% of the studies attempted replication of the US Diabetes Prevention Program or the Finnish Diabetes Prevention Study (with some modifications). Despite a minimum three-month intervention duration being specified in the inclusion critiera, it was noted that the intervention duration in one study was only one month.
The authors did not state how many reviewers performed study selection.