The Effect of Onion Peel Extract on Inflammatory Mediators in Korean Overweight and Obese Women

Quercetin, found abundantly in onion peel, has been known to have antioxidant and anti-obesity effects and improves endothelial function. The purpose of this study was to evaluate the effects of a quercetin-rich onion peel extract (OPE) on the inflammatory mediators in overweight and obese women. This study was a randomized double-blind, placebo-controlled study. Thirty-seven healthy overweight and obese women were randomly assigned to two groups, and one group was given a soft capsuled OPE (100 mg quercetin/day, n = 18) and the other group a same capsuled placebo (n = 19) for 12 weeks. Fat mass was measured by bioimpendance method at baseline and after 12 weeks of intervention. The levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured with colorimetric assay kits. The concentrations of leptin, adiponectin, visfatin, tumor necrosis factor (TNF)-α and interleukin (IL)-4 in plasma were determined by using enzyme-linked immunosorbent assay kits. Baseline characteristics of anthropometric indicators and blood metabolic profiles were not significantly different between placebo and OPE groups. Compared with baseline value, both placebo and OPE supplementation significantly decreased the percent of body fat mass and induced plasma adiponectin levels while ALT and AST activities as well as leptin, visfatin, TNF-α, and IL-4 levels in plasma were not significantly different between two groups after 12 weeks of the supplementation. These findings suggest that 12-week supplementation of OPE do not affect modulators of systemic inflammation in overweight and obese women.

Onion peel extract reduces the percentage of body fat in overweight and obese subjects: a 12-week, randomized, double-blind, placebo-controlled study

BACKGROUND/OBJECTIVES: The anti-obesity effect of quercetin-rich onion peel extract (OPE) was suggested in rats, but information from human studies is limited. This study aimed to investigate the effects of OPE on the body composition of overweight and obese subjects. MATERIALS/METHODS: In this 12-week, randomized, double-blind, placebo-controlled study, parallel clinical trials were performed in overweight and obese Korean subjects. Randomly assigned subjects were instructed to take daily either the placebo (male, 6 and female, 30) or OPE capsules containing 100 mg of quercetin (male, 5 and female, 31). Body composition was measured by using bioimpedance and dual-energy X-ray absorptiometry (DXA). Resting energy expenditure (REE) and respiratory quotient (RQ) were evaluated by using indirect calorie measurement methods. Fasting blood levels of glucose, insulin, lipids, and leptin were determined. RESULTS: Quercetin-rich OPE supplementation significantly reduced the weight and percentage of body fat as measured by DXA (P = 0.02). These effects were not shown in the control group. Levels of blood glucose (P = 0.04) and leptin (P = 0.001 for placebo, P = 0.002 for OPE) decreased in both groups. Significant increases in REE and RQ were observed in both groups (P = 0.003 for placebo, P = 0.006 for OPE) and in the OPE group alone (P = 0.02), respectively. CONCLUSIONS: Quercetin-rich OPE supplementation changed the body composition of the overweight and obese subjects. This result suggests a beneficial role of the anti-obesity effect of OPE human subjects.

Antioxidative Activity of Onion Peel Extract in Obese Women: A Randomized, Double-blind, Placebo Controlled Study

BACKGROUND: Quercetin, found abundantly in onion peel, has been known to have anticholesterol, antithrombotic and insulin-sensitizing properties. Here, we investigated the effect of quercetin-rich onion peel extract (OPE) on reactive oxygen species (ROS) production and antioxidative defense in obese woman. METHODS: This study was randomized, double-blind, placebo controlled study. Thirty-seven healthy obese participants were randomly assigned that eighteen subjects received red soft capsuled OPE (100 mg/d, 50 mg bis in die), while the other nineteen subjects received same capsuled placebo for 12 weeks. ROS production and superoxide dismutase (SOD) activity in plasma were determined by using ROS and SOD assay kits, respectively. RESULTS: Baseline characteristics of anthropometric indicators and blood metabolic profiles were not significantly different between the two groups. Compared with baseline values, OPE consumption significantly reduced waist and hip circumference. Plasma ROS level and SOD activity were decreased in both placebo and OPE groups compared with baseline values. However, plasma ROS level in OPE group was significantly lower than in placebo group while plasma SOD activity in OPE group was significantly higher than in placebo group after 12 weeks of consumption. CONCLUSIONS: These findings indicate that OPE consumption may exert antioxidative effect by preventing the decrease of SOD activity as well as the production of ROS in obese women.

Onion peel water extracts enhance immune status in forced swimming rat model / 한국실험동물학회지

Onion peel contains a high concentration of quercetin and other flavonoids. In this study, the potential immune-enhancing effects of an onion peel water extract (OPE) supplement were investigated by the rat forced swimming test. OPE was prepared using hot water. Thirty-six male Sprague Dawley rats were fed a pellet diet for 1 week and were then randomly divided into six groups: normal control (NC), forced swimming control (FSC), positive control (quercetin 20 mg/kg), and three groups administered 4, 20, or 100 mg/kg of OPE. Oral drug administration was conducted daily for 4 weeks. All rats, except those of NC group, were forced to swim in water and were considered exhausted when they failed to rise to the water surface to breathe within a 7-s period. Blood lymphocyte counts, immune organ weights, histopathological analysis, and serum interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-12 levels were determined. OPE-treated rats consumed more food and had an increased thymic cortex to medulla ratio than that observed in FSC group rats (P<0.05). The area of the white pulp in the spleens of OPE-treated group rats was increased compared with that in FSC group rats (P<0.05). Furthermore, blood lymphocyte numbers and IFN-gamma, TNF-alpha, and IL-12 concentrations were significantly higher in OPE-fed groups than in FSC group (P<0.05). These results suggest that an OPE supplement can improve the immune status by increasing the number of immune-related cells and specific cytokine levels.

Effect of onion peel extract supplementation on the lipid profile and antioxidative status of healthy young women: a randomized, placebo-controlled, double-blind, crossover trial

The consumption of fruits and vegetables that have high polyphenol content has been previously associated with a reduced risk for cardiovascular disease. We investigated the effects of onion peel extract on plasma total antioxidant capacity, lipid peroxidation, and leukocyte DNA damage. This study was a randomized, double-blind, placebo-controlled, crossover trial. Healthy female subjects received either onion peel extract or placebo (dextrin) for two weeks, underwent a 1-week washout period, and then received the other treatment for an additional two weeks. After two weeks of onion peel extract supplementation, the total cholesterol level, low-density lipoprotein cholesterol level, and atherogenic index significantly decreased (P < 0.05). No changes were observed in activities of erythrocyte antioxidant enzymes or levels of lipid peroxidation markers following onion peel extract supplementation. Additionally, no significant difference was found in plasma antioxidant vitamin (retinol, tocopherols, carotenoids, and coenzyme Q10) levels or ex vivo H2O2-provoked oxidative DNA damage after onion peel extract supplementation. The present interventional study provides evidence of the health benefits of onion peel extract and demonstrates its effects in modulating lipid profiles in healthy young Korean women.

Effects of onion peel water extracts on swimming endurance in rat / 동물의과학연구지

Onion (Allium cepa L.) contains high levels of dietary fibers and antioxidants, including vitamin C, D, and folates. Onion is also known as a quercetin-rich vegetable with high flavonoid content. Onion peel contains over 20 times more quercetin than onion flesh. The aim of this study was to examine the question of whether onion peel extract supplementation has an effect on maximal exercise performance in rat. Onion peel extracts were extracted with hot water. Thirty male Sprague Dawley rats were maintained on a pellet diet for one week, and then randomly divided into five groups: Normal control, Positive control (quercetin 20 mg/kg), Onion peel 4 mg/kg, Onion peel 20 mg/kg, and Onion peel 100 mg/kg. Oral administration was performed daily. The experimental period was four weeks. Thereafter, animals were then forced to swim in water and the maximal exercise performance period from the swimming start time to the exhausted time, in which they failed to rise to the surface of the water to breathe within a 7 second period, was measured. After necropsy, weights of gastrocnemius muscles were measured. Lactate dehydrogenase concentration in serum was measured using an enzymatic method, using a commercial kit. The maximal exercise performance period was significantly longer in the onion peel extracts fed groups, compared with the control group. The lactate dehydrogenase concentration of the onion peel extracts fed groups was significantly lower, compared with the control group. Based on these results, we suggest that onion peel water extract supplementation can enhance exercise capacity caused by the mechanism of decreasing lactate dehydrogenase concentration.

Antioxidant Effects on various solvent extracts from Onion Peel and Onion Flesh

This study was designed to investigate the role of onion as a natural antioxidant. Onion was distinguished as yellow onion peel and onion flesh. Onion samples were extracted with 5 different kinds of solvents such as water, 70% ethanol, 99.9%ethanol, 99.9% methanol, and 96% butanol in order to select optimal extraction solvents, In this part of study linoleic acid was used s an model system for the purpose of determining the antioxidant activities. The optimal extraction rate of various solvents containing onion samples was determined by measuring extraction yield, electron donating ability(EDA), thiobarbituric acid(TBA), and thiocyanate, which are common methods for measuring activity. As a result 70% ethanol was shown as the most effective solvent.