Positive effects of garlic on insulin resistance and other indices of glucose metabolism: A systematic review of clinical trials

Insulin resistance (IR) causes various metabolic disorders depending on the individual's genetic background. It can be detected up to 10-15 years before a person develops type 2 diabetes mellitus. The prevalence of diabetes is projected to increase from 8.4% in 2017 to 9.9% in 2045. Garlic has been used as herbal medicine. It has various biological effects such as anti-inflammatory, anti-diabetic, and antioxidants. The present study aims to investigate the impact of garlic on IR and other indices of glucose metabolism. Electronic databases including PubMed, Google Scholar, ScienceDirect, Science Information Database (SID), and publisher databases such as Elsevier, SpringerLink, and Wiley Online Library were searched till February 2022. Search terms involved “garlic” OR “Allium sativum” OR “alliin” OR “allicin” in combination with “fasting blood glucose” OR “fasting plasma glucose” OR “fasting blood sugar” OR “insulin resistance” OR “fasting insulin” OR “homeostasis assessment model” OR “HOMA” AND “polycystic ovary syndrome” OR “diabetes mellitus” OR “type 2 diabetes mellitus” OR “metabolic syndrome” OR “nonalcoholic fatty liver disease” OR “cardiovascular diseases”. After reviewing the databases mentioned seven articles were identified for this review. Totally, 459 participants including 228 women and 231 men, enrolled in the trials. Assessing the findings of these articles indicate that garlic has a positive effect on IR, plasma insulin, and fasting glucose. The hypoglycemic action of garlic is related to its sulfur-containing compounds which directly or indirectly stimulate insulin secretion. Also, allicin in garlic can combine with endogenous thiol-containing molecules which can release insulin from inactivation.