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 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 antidiabetic medications. The comparative studies had to include a usual care group (no active diet and physical activity promotion program) or a lower-intensity diet and physical activity promotion program (for example, one with fewer contact sessions or a more liberal diet). We required at least 6 months of follow-up for any of the following outcomes: incident diabetes, reversion to normoglycemia, body weight, glycemic measures (fasting glucose level, 2-hour glucose level after a 75-g oral glucose tolerance test, or hemoglobin A1c [HbA1c] level), all-cause death, diabetes-related clinical outcomes (such as cardiovascular events, end-stage renal disease, nephropathy, amputation, retinopathy, neuropathy, skin ulcers, or periodontitis), BP, and lipid levels (total, low-density lipoprotein [LDL], and high-density lipoprotein [HDL] cholesterol and triglycerides). Data Extraction and Quality Assessment We screened titles and abstracts using Abstrackr (17). Eight researchers double-screened the abstracts after iterative training of all reviewers on the same batches of abstracts. Discordant decisions and queries were resolved at group meetings. Full-text articles were retrieved for all potentially relevant abstracts and rescreened by the same researchers. Data from each study were extracted by 1 of 7 experienced methodologists and confirmed by a senior methodologist; the same methodologists assessed study quality. Data extraction was conducted in the Systematic Review Data Repository (18) and included elements for study design, including eligibility criteria, population characteristics, detailed descriptions of the diet and physical activity promotion programs and comparison interventions, outcomes, and results. We assessed the quality of each study by using 12 Community Guide quality-of-execution questions (see the footnotes of Table 2 of the Supplement) (14, 19). Per Community Guide protocol, we excluded studies with "limited quality of execution," defined as those with at least 5 major limitations. Data Synthesis and Analysis All extracted data were placed into summary evidence tables (available in the supporting materials at www.thecommunityguide.org/diabetes/combineddiet andpa.html). Two studies that were conducted in children were not included in the meta-analyses and are reported separately. For outcomes with data from at least 3 comparative studies of diet and physical activity promotion versus usual care, we performed meta-analysis of the risk ratio (RR) or net change (20) using a profile likelihood random-effects model. For nonrandomized studies, we preferentially used results of adjusted analyses. Meta-analyses were conducted with the metaan package in Stata 13.1 (StataCorp). For the overall meta-analyses of incident diabetes and reversion to normoglycemia, we used data from the longest reported follow-up. For continuous outcomes, we used data closest to 1 year of follow-up and those from the longest follow-up. We evaluated differences in effect (for incident diabetes and weight only) using direct comparisons of different diet and physical activity promotion programs within studies, reported within-study subgroup analyses, and across-study metaregression (based on predetermined study setting and program features and using a random-effects model) across all programs. Incident diabetes and weight change were chosen for metaregression because of their relative importance in determining the effectiveness of diet and physical activity promotion programs. Metaregressions were conducted with the metareg package in Stata and were considered potentially significant if the P value was less than 0.10. For each outcome with at least 10 studies, we examined the possibility of publication bias with funnel plots and the Harbord test (for diabetes incidence) or the Egger test (for continuous outcomes) using the metabias and metafunnel packages in Stata (21). Role of the Funding Source One member of the Coordination Team and our Technical Moni