The antidiabetic effect of onion and garlic in experimental diabetic rats: meta-analysis.
ABSTRACT This study was carried out to evaluate the effect of onion and garlic in experimentally induced diabetic rats by meta-analysis of related studies. Ten systematic literature searches were conducted on the National Center for Biotechnology Information database, the DBpia database, and the Koreanstudies Information Service System database. Most studies had three groups-the normal group, the treated diabetic group, and the untreated diabetic group-the means of which were compared for various effect factors between two of the groups. The effect factors were blood glucose concentration, body weight, and the concentrations of plasma total cholesterol, plasma triglycerides, plasma high-density lipoprotein-cholesterol, and liver glycogen. The treated diabetic group included diabetic rats supplemented with either onion or garlic extract or with single components, including S-allylcysteine sulfoxide, S-methylcysteine sulfoxide, and diallyl trisulfide. The effects of each factor were investigated by the standardized mean difference between the treated diabetic group and the diabetic group. Because homogeneity among studies for some effect factors is not plausible, the random effect estimates were calculated. In the meta-analysis, the antidiabetic effects of onion extract and single components were significant for glucose concentration and body weight (P < .05), but the effects of garlic extract were not significant. The results of the meta-analysis suggested that the single component intake and onion extract intake may be effective for lowering plasma glucose concentrations and body weight.
Article: Onion peel extracts ameliorate hyperglycemia and insulin resistance in high fat diet/streptozotocin-induced diabetic rats.[show abstract] [hide abstract]
ABSTRACT: Quercetin derivatives in onions have been regarded as the most important flavonoids to improve diabetic status in cells and animal models. The present study was aimed to examine the hypoglycemic and insulin-sensitizing capacity of onion peel extract (OPE) containing high quercetin in high fat diet/streptozotocin-induced diabetic rats and to elucidate the mechanism of its insulin-sensitizing effect. Male Sprague-Dawley rats were fed the AIN-93G diet modified to contain 41.2% fat and intraperitoneally injected with a single dose of streptozotocin (40 mg/kg body weight). One week after injection, the rats with fasting blood glucose levels above 126 mg/dL were randomly divided into 4 groups to treat with high fat diet containing 0 (diabetic control), 0.5, or 1% of OPE or 0.1% quercetin (quercetin equivalent to 1% of OPE) for 8 weeks. To investigate the mechanism for the effects of OPE, we examined biochemical parameters (insulin sensitivity and oxidative stresses) and protein and gene expressions (pro-inflammatory cytokines and receptors). Compared to the diabetic control, hypoglycemic and insulin-sensitizing capability of 1% OPE were demonstrated by significant improvement of glucose tolerance as expressed in incremental area under the curve (P = 0.0148). The insulin-sensitizing effect of OPE was further supported by increased glycogen levels in liver and skeletal muscle (P < 0.0001 and P = 0.0089, respectively). Quantitative RT-PCR analysis showed increased expression of insulin receptor (P = 0.0408) and GLUT4 (P = 0.0346) in muscle tissues. The oxidative stress, as assessed by superoxide dismutase activity and malondialdehyde formation, plasma free fatty acids, and hepatic protein expressions of IL-6 were significantly reduced by 1% OPE administration (P = 0.0393, 0.0237, 0.0148 and 0.0025, respectively). OPE might improve glucose response and insulin resistance associated with type 2 diabetes by alleviating metabolic dysregulation of free fatty acids, suppressing oxidative stress, up-regulating glucose uptake at peripheral tissues, and/or down-regulating inflammatory gene expression in liver. Moreover, in most cases, OPE showed greater potency than pure quercetin equivalent. These findings provide a basis for the use of onion peel to improve insulin insensitivity in type 2 diabetes.Nutrition & Metabolism 03/2011; 8(1):18. · 2.88 Impact Factor