Efficacy of flavonoids-containing supplements on insulin resistance and associated metabolic risk factors in overweight and obese subjects: a systematic review and meta-analysis of 25 randomized controlled trials

Systematic review and meta-analysis of 25 randomized controlled trials including 1950 overweight or obese adults. Populations included postmenopausal women, patients with hypertension, dyslipidemia, metabolic syndrome, polycystic ovary syndrome, impaired fasting glycemia, type 2 diabetes, and some healthy overweight participants.

Oral flavonoids-containing supplements were tested in varied forms, including capsules, tablets, beverages, and powders, with doses and durations differing by product. Regimens included flavonoid mixtures and single compounds such as isoflavones, green tea extract or EGCG, quercetin, bergamot extract, hesperidin, resveratrol, and other flavonoid-rich products, compared with placebo or control.

Overall, flavonoids-containing supplements improved insulin resistance and several cardiometabolic risk factors in overweight and obese adults. HOMA-IR decreased modestly versus control (WMD = -0.13, 95% CI: -0.24 to -0.03; p = 0.013), with a stronger effect for flavonoid mixtures (WMD = -0.25, 95% CI: -0.43 to -0.06; p = 0.008) and no clear benefit for single flavonoids (WMD = -0.08, 95% CI: -0.20 to 0.05; p = 0.240). Fasting glucose, fasting insulin, total cholesterol, triglycerides, systolic blood pressure, BMI, and waist-hip ratio also improved, while QUICKI did not show a clear overall difference. Adverse events were not increased (RR = 0.97, 95% CI: 0.62 to 1.52; p = 0.905), supporting good tolerability.

The evidence base was limited by small, heterogeneous trials with varying flavonoid sources, doses, formulations, and treatment durations. Several studies had incomplete or inconsistently reported participant details, and long-term efficacy and safety remain uncertain. Additional high-quality trials are needed to clarify the most effective flavonoid types and dosing strategies.