Effects of Garcinia mangostana Peel Extract on Glycemic Control in Type 2 Diabetes Mellitus: A Systematic Review of Human Studies

Introduction: Type 2 diabetes mellitus (T2DM) is a major global health concern characterized by insulin resistance, hyperglycemia, and chronic inflammation. Interest in natural adjunctive therapies has increased, particularly in mangosteen (Garcinia mangostana), which contains xanthone compounds in the peel with potential antidiabetic properties. Methods: This systematic review followed PRISMA 2020 guidelines. Literature searches were conducted using PubMed, Google Scholar, and ClinicalKey up to December 2022 for studies assessing mangosteen peel extract (MPE) or α-mangostin in diabetic human subjects. Eligible studies included randomized controlled and quasi-experimental trials reporting glycemic or metabolic outcomes. Risk of bias was evaluated using the Cochrane RoB tool. The primary result of this study is to evaluate the effects of mangosteen peel extract supplementation on key glycemic outcomes in patients with T2DM, specifically fasting blood glucose (FBG), HOMA-IR, and HbA1c. Results: A total of two studies (n=2) met the inclusion criteria. A randomized controlled pilot trial reported significant improvement in insulin sensitivity (HOMA-IR −53.2% vs −15.2%; p = 0.004) after 26 weeks of standardized mangosteen extract. A small quasi-experimental study reported a significant reduction in FBG following 7 days of mangosteen peel decoction. Discussion: Limited clinical evidence indicates that mangosteen peel extract may improve insulin sensitivity and lower fasting glucose in T2DM. However, the conclusions are limited by the small number of available studies, the short follow-up duration in one trial, and variability in extract preparation. Conclusion: Mangosteen peel extract demonstrates promising glycemic benefits, including improved insulin sensitivity and reduced fasting glucose. However, the available evidence remains limited by small sample sizes, short follow-up periods, and heterogeneity in extract formulations. Larger randomized controlled trials using standardized preparations are required before clinical recommendations can be made.