A systematic review of structured weight loss programs and their association with HbA1c reduction in adults with prediabetes managed in primary care

BACKGROUND: Prediabetes, marked by elevated blood glucose levels below the type 2 diabetes mellitus (T2DM) threshold, is a growing public health concern due to its rising prevalence and risk of progression to diabetes and cardiovascular issues. Structured weight loss programs in primary care show promise for improving glycemic control, yet their impact on HbA1c remains underexplored. This systematic review evaluates their effectiveness in reducing HbA1c in adults with prediabetes. METHODS: Following PRISMA 2020 and SWiM guidelines, we searched six databases (PubMed, EMBASE, Cochrane CENTRAL, Scopus, CINAHL, Web of Science) through July 10, 2025, for studies evaluating structured weight-loss interventions delivered in primary care. Eligible studies included adults (≥18 years) with prediabetes and used randomized trials, cohort designs, or pilot interventions reporting HbA1c as a primary outcome. Risk of bias was assessed using the original Cochrane RoB tool for randomized studies. Narrative synthesis was conducted due to substantial heterogeneity in design, intervention intensity, and analytical approaches. RESULTS: Six studies (n = 45-2818) showed HbA1c reductions, with high-intensity (frequent behavioral sessions) and digital interventions (low-carbohydrate apps) yielding the largest effects. Weight loss (up to 4.08 kg), BMI, and lipid profiles also improved. Adherence and intervention intensity were key factors, though inconsistent reporting limited comparisons. CONCLUSION: Structured weight loss programs in primary care are associated with modest-to-moderate HbA1c reductions. However, study heterogeneity, analytical methods and inconsistent adherence reporting limit definitive conclusions. Future research should prioritize standardized reporting, long-term outcomes, and diverse populations to enhance generalizability.