BackgroundThis 7 year NIHR programme [2011–2018] tests the primary hypothesis that the NDPS diet and physical activity intervention will reduce the risk of transition to type 2 diabetes (T2DM) in groups at high risk of Type 2 diabetes. The NDPS programme recognizes the need to reduce intervention costs through group delivery and the use of lay mentors with T2DM, the realities of normal primary care, and the complexity of the current glycaemic categorisation of T2DM risk.MethodsNDPS identifies people at highest risk of T2DM on the databases of 135 general practices in the East of England for further screening with ab fasting plasma glucose and glycosylated haemoglobin [HbA1c]. Those with an elevated fasting plasma glucose [impaired fasting glucose or IFG] with or without an elevated HbA1c [non -diabetic hyperglycaemia; NDH] are randomised into three treatment arms: a control arm receiving no trial intervention, an arm receiving an intensive bespoke group-based diet and physical activity intervention, and an arm receiving the same intervention with enhanced support from people with T2DM trained as diabetes prevention mentors [DPM]. The primary end point is cumulative transition rates to T2DM between the two intervention groups, and between each intervention group and the control group at 46 months. Participants with screen detected T2DM are randomized into an equivalent prospective controlled trial with the same intervention and control arms with glycaemic control [HbA1c] at 46 months as the primary end point. Participants with NDH and a normal fasting plasma glucose are randomised into an equivalent prospective controlled intervention trial with follow up for 40 months. The intervention comprises six education sessions for the first 12 weeks and then up to 15 maintenance sessions until intervention end, all delivered in groups, with additional support from a DPM in one treatment arm.DiscussionThe NDPS programme reports in 2018 and will provide trial outcome data for a group delivered diabetes prevention intervention, supported by lay mentors with T2DM, with intervention in multiple at risk glycaemic categories, and that takes into account the realities of normal clinical practice.Trial registration ISRCTN34805606 (Retrospectively registered 16.3.16)Electronic supplementary materialThe online version of this article (doi:10.1186/s12889-016-3929-5) contains supplementary material, which is available to authorized users.

Question Does our group-based lifestyle intervention (with or without trained volunteers with Type 2 diabetes) reduce the risk of Type 2 diabetes in people with the current high risk intermediate glycemic categories of impaired fasting glucose or non-diabetic hyperglycemia Finding In this trial of 1,028 participants with high risk intermediate glycemic categories , the intervention significantly reduced the 2 year risk of Type 2 diabetes by 40-47%, although lay volunteer support did not reduce the risk further. For every 11 participants treated, one diabetes diagnosis was prevented. Meaning Nearly half the adult population have diabetes or a high risk glycemic category, and this low-cost group-delivered intervention significantly reduced the risk of diabetes.

ObjectiveIntensive lifestyle interventions reduce the risk of type 2 diabetes in populations at highest risk, but staffing levels are usually unable to meet the challenge of delivering effective prevention strategies to a very large at-risk population. Training volunteers with existing type 2 diabetes to support healthcare professionals deliver lifestyle interventions is an attractive option.MethodsWe identified 141 973 people at highest risk of diabetes in the East of England, screened 12 778, and randomized 1764 into a suite of type 2 diabetes prevention and screen detected type 2 diabetes management trials. A key element of the program tested the value of volunteers with type 2 diabetes, trained to act as diabetes prevention mentors (DPM) when added to an intervention arm delivered by healthcare professionals trained to support participant lifestyle change.ResultsWe invited 9951 people with type 2 diabetes to become DPM and 427 responded (4.3%). Of these, 356 (83.3%) were interviewed by phone, and of these 131 (36.8%) were interviewed in person. We then appointed 104 of these 131 interviewed applicants (79%) to the role (mean age 62 years, 55% (n=57) male). All DPMs volunteered for a total of 2895 months, and made 6879 telephone calls to 461 randomized participants. Seventy-six (73%) DPMs volunteered for at least 6 months and 66 (73%) for at least 1 year.DiscussionIndividuals with type 2 diabetes can be recruited, trained and retained as DPM in large numbers to support a group-based diabetes prevention program delivered by healthcare professionals. This volunteer model is low cost, and accesses the large type 2 diabetes population that shares a lifestyle experience with the target population. This is an attractive model for supporting diabetes prevention efforts.

What is already known on this subject?Many health interventions, including programmes to help prevent or manage diabetes and facilitate weight loss, are delivered in groups. Such group-based behaviour-change interventions are often effective in facilitating psychological and behaviour change. There is considerable research and theory on individual change processes and techniques, but less is known about which change processes and techniques facilitate behaviour change in group settings. What does this study add?This study contributes to our understanding of how participating in group-based health programmes may enhance or impede individual behaviour change. It identified individual (intrapersonal) and group (interpersonal, facilitated through group interaction) change processes that were valued by group participants. The findings also show how these change processes may be affected by the group context. A diagram summarizes the identified themes helping to understand interactions between these key processes occurring in groups.The study offers an insight into participants' views on, and experiences of, attending a group-based diabetes prevention and management programme. Thus, it helps better understand how the intervention might have helped them (or not) and what processes may have influenced intervention outcomes. Key practical recommendations for designing and delivering group-based behaviour-change interventions are presented, which may be used to improve future group-based health interventions.