Effects of Garlic on Glucose Parameters and Lipid Profile: A Systematic Review and Meta-Analysis on Randomized Controlled Trials.

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• Garlic may help lower high blood sugar levels, especially for people with type 2 diabetes.
• It can reduce LDL cholesterol and increase the beneficial HDL cholesterol, supporting heart and vascular health.
• For best results, garlic should be used consistently over time.

Introduction

• This study aimed to assess the effects of garlic consumption on glucose parameters and lipid profiles in humans.
• It sought to resolve conflicting evidence regarding garlic's impact on fasting blood glucose (FBG), glycosylated hemoglobin (HbA1c), total cholesterol (TC), HDL, LDL, and triglycerides (TG).
• The research applied a systematic review and meta-analysis approach to randomised controlled trials (RCTs).

Methods

RCTs from four databases (PubMed, Embase, Web of Science, Cochrane Library) were reviewed until February 2024, in accordance with the PRISMA 2020 guidelines. The review included 22 studies with a total of 1567 participants. The trials used different forms of garlic mainly in supplement form (e.g., tablets, powder, aged garlic extract) and various doses over intervention durations ranging from 3 weeks to 1 year.

Results

Garlic significantly:

• reduced FBG (mean difference: -7.01 mg/dL, 95% CI: -8.53 to -5.49, p < 0.001) and HbA1c (mean difference: -0.66%, 95% CI: -0.76 to -0.55, p < 0.001).
• decreased TC (mean difference: -14.17 mg/dL, p < 0.001) and LDL (mean difference: -8.20 mg/dL, p = 0.03)
• increased HDL (mean difference: +2.06 mg/dL, p < 0.001).

Subgroup analyses suggested more pronounced effects for longer intervention durations (>8 weeks) and in participants with type 2 diabetes (T2DM). Garlic had no significant effect on TG levels (p = 0.125).

Conclusion

• In studies with intervention durations >= 8 weeks, garlic was effective in improving blood glucose and lipid profiles, particularly in lowering FBG, HbA1c, TC, and LDL, while raising HDL.
• Garlic may be beneficial for conditions related to glucose and lipid metabolism, even though it had no significant effect on TG levels.

• Garlic supplementation can be recommended to lower FBG and HbA1c, aiding in glycemic control for patients with T2DM through enhanced insulin sensitivity, stimulation of insulin secretion and reduced oxidative stress that may benefit glycaemic control.
• Practitioners can use garlic as part of nutritional strategies to reduce TC and LDL, potentially reducing cardiovascular risk.
• Garlic may increase HDL levels, making it a useful addition to lipid management protocols, though an effective minimum dose is unclear due to study variations (300–22,400 mg daily) and differing active compounds such as allicin and S-allyl cysteine. This variability limits specific dosing recommendations.
• Garlic use longer than 8 weeks is more effective, suggesting sustained dietary supplementation for enhanced benefits.
• No significant impact on triglycerides indicates practitioners should combine garlic with other interventions for TG management.

• Investigate the long-term effects of garlic on TG levels, given the lack of significant findings in current studies.
• Explore the mechanisms behind garlic’s differential impact on FBG in non-diabetic populations.
• Conduct trials with standardised garlic formulations to reduce variability in active compounds.
• Examine garlic’s role in improving insulin sensitivity and HOMA-IR across various metabolic conditions.
• Study the effects of combining garlic with other dietary interventions to enhance lipid profile improvements such as omega-3 fatty acids, fibre supplements, and plant sterols.