Combined Diet and Physical Activity Promotion Programs to Prevent Type 2 Diabetes Among Persons at Increased Risk: A Systematic Review for the Community Preventive Services Task Force

Diabetes is a large and growing medical problem, and the costs to society are high and escalating. According to the latest figures from the Centers for Disease Control and Prevention (CDC), 29.1 million persons (9.3% of the U.S. population) have diab... show more

Diabetes is a large and growing medical problem, and the costs to society are high and escalating. According to the latest figures from the Centers for Disease Control and Prevention (CDC), 29.1 million persons (9.3% of the U.S. population) have diabetes, and 1.7 million new cases are diagnosed annually (1). Worldwide, an estimated 387 million adults are living with diabetes, and this number is projected to increase to 592 million by 2035 (2). Prevalence of diabetes and related costs are expected to more than double in the next 25 years (3), given that in excess of 86 million Americans (37% of the adult population) are at risk for the disease (1). Effective prevention strategies are, therefore, crucial to slow the diabetes tide and its associated burden. Nearly 9 out of 10 new diabetes cases are type 2 diabetes, which has a natural history characterized by a gradual increase in glycemia. Identification of persons at increased risk can enable the implementation of interventions to decrease the risk for progression to clinical diabetes. The American Diabetes Association has defined prediabetes as a high-risk category based on a glycemic level that does not meet criteria for diabetes but is too high to be considered normal (4). Persons with prediabetes progress to type 2 diabetes at a rate of about 5% to 10% per year without intervention (5). Three large clinical trials from the United States (6), Finland (7), and China (8) have shown that the primary components of diabetes prevention in adults are weight loss and increased physical activity. In these trials, among persons at risk for type 2 diabetes, rigorous application of combined diet and physical activity promotion programs, with the goals of weight loss and increased physical activity, reduced risk for diabetes by 50% to 60% during the active intervention period (3 to 6 years). Although attenuated, the effect of the intervention can persist in the long term (911). The results of these trials are well-known; however, wide-scale implementation of combined diet and physical activity promotion programs in clinical and community-based settings has only recently begun and requires further expansion (12). Combined diet and physical activity promotion programs aim to prevent type 2 diabetes among persons who are at increased risk for the disease. These programs actively encourage persons to improve their diet and increase physical activity by using trained providers in various settings who work with clients for at least 3 months, providing some combination of counseling, coaching, and extended support in multiple sessions (delivered in person or by other methods) related to diet and physical activity. Programs may also include many other features, including specialized counselors; a range in the number and frequency of sessions; different session types; and different diet, weight-loss, or exercise goals. The purpose of this review was to assess the effectiveness of diet and physical activity promotion programs implemented in a wide range of clinical or community settings to reduce risk for new-onset diabetes among adults and children at risk for type 2 diabetes. The Community Preventive Services Task Force (Task Force) (www.thecommunityguide.org) used this review to update its guidance on diabetes prevention and to identify gaps in the evidence to inform future research. Potential effect modifiers, such as intensity and specificity of the programs, settings, and implementers, were evaluated. Furthermore, the potential benefit of the diabetes prevention programs extending to other cardiometabolic risk factors, such as overweight, high cholesterol level, and high blood pressure (BP), was also assessed. Methods This review was conducted in accordance with the methods of the Task Force (13, 14) and the highest standards for conducting systematic reviews (15, 16). We convened a panel of domain experts and stakeholders (Coordination Team) that, together with our Community Guide Technical Monitor and Task Force members, provided input on the protocol, feedback on the findings, conclusions, and evidence gaps. Data Sources We searched MEDLINE, the Cochrane Central Register of Controlled Trials, CAB Abstracts, Global Health, and Ovid HealthSTAR from 1991 through 27 February 2015 with no language restrictions. Table 1 of the Supplement shows the search strategy. We also screened reference lists of related systematic and narrative reviews and suggestions from the expert panel. Supplement. Supporting Information Study Selection We included randomized, controlled trials and prospective nonrandomized comparative studies with at least 30 participants per group, as well as prospective single-group intervention studies with at least 100 participants. The population of interest was adults or children at increased risk for type 2 diabetes (that is, with prediabetes) as determined by glycemic measures or diabetes risk assessment tools. We included studies of participants with the metabolic syndrome (who are at increased risk for both diabetes and cardiovascular disease) and studies with participants who were chosen because they were at risk for either type 2 diabetes or cardiovascular disease. However, we excluded studies of participants with established type 2 diabetes or whose only risk factor was obesity or increased risk for cardiovascular disease (without explicit inclusion of participants with prediabetes). The implied or explicit intent of the diet and physical activity promotion programs had to be to prevent diabetes, and the programs had to include at least 2 contact sessions (in-person or virtual) over at least 3 months. Programs had to include both dietary and increased physical activity components and could be conducted in any outpatient setting. We allowed any type of advice to improve diet and increase physical activity (except for single-food or supplement dietary changes, such as addition of fish oil). We excluded interventions that included antid show less