Onion, a world-class superfood, is versatile in various cuisines and offers valuable health benefits. It can aid in weight loss, lower blood sugar, and help prevent cancer and dementia.
Onions are a great source of nutrients such as folate, calcium, iron, dietary fiber, vitamin B6, vitamin C, and potassium. Additionally, they are low in calories and contain no fat or cholesterol.
Onions contain natural chemical compounds, such as organosulfur, and flavonoids like quercetin, which can help fight disease and promote health.
In a clinical trial, 70 overweight participants were randomly divided into two groups. They were given either a placebo or a steamed onion supplement before each meal for 12 weeks. The results showed that taking the steamed onion supplement reduced total body fat, especially abdominal visceral fat.
A study of 72 overweight and obese Korean subjects established that those who consumed onion peel extract, which is rich in quercetin, experienced significant reductions in body weight and body fat percentage, indicating that onion peel extract has a potential anti-obesity effect.
Onion extract can regulate cholesterol, improve antioxidant capacity, and suppress inflammatory markers, thereby attenuating the incidence of cardiovascular disease. In a study, researchers discovered that onion had better cardio-protective effects than red wine.
In a study of 70 overweight-to-obese subjects with pre-hypertension and stage I hypertension, researchers found that the onion skin extract quercetin could lower blood pressure.
Quercetin in onions can combat oxidative stress associated with neurodegenerative disorders such as Alzheimer’s, according to a study on the neuropotential role of quercetin.
Scientists have found that onions can attenuate stress-induced anxiety and depression in mice and enhance their memory function.
Onion extract exhibits anti-proliferative and anti-migratory effects on human adenocarcinoma (Caco-2) cells, indicating that it may be an effective anti-cancer therapy.
Researchers in Japan found that a natural compound called onionin A (ONA) isolated from onions can inhibit the progression of ovarian cancer by suppressing the protumor function of macrophages and reducing cancer cell proliferation.
An analysis of national health data revealed that women who consumed onions daily had 5 percent higher overall bone density than those who consumed onions once a month or less.
Using fresh red onion juice as eye drops in an animal experiment, researchers found that onion had an inhibitory effect on the growth of normal bacterial flora on the conjunctiva and eyelid surfaces.
In a separate animal experiment, researchers instilled fresh onion juice into the eyes of rats and discovered that onion juice can effectively prevent the formation of selenite-induced cataracts.
In a clinical trial, 38 patients with alopecia areata were treated with topical crude onion juice, which researchers discovered could promote hair re-growth and serve as an effective topical therapy to treat patchy alopecia areata.
In a study of 30 healthy men and women who were dissatisfied with their sleep quality, the subjects were given onion extract tablets containing concentrated cysteine sulfoxides; the results showed that these tablets may improve sleep quality and promote a smooth transition into sleep.
A study revealed that the phenolic extract from onion bulbs could induce human immune cell proliferation, particularly the growth of CD16+ natural killer cells, which have anti-tumor and anti-infection effects.
An animal study confirmed that regular consumption of onions could prevent nonalcoholic fatty liver disease even in the presence of other risk factors (such as hypercholesterolemia, obesity, and high intake of energy, fat, and sugar).
Consuming fresh yellow onions can effectively ameliorate hyperglycemia and insulin resistance in breast cancer patients during chemotherapy, according to the results of a clinical trial.
A study showed that onions have a preventive effect on lung inflammation and can reduce tracheal responsiveness in asthmatic animals.
An animal study revealed that onions can enhance and protect testicular function and architecture from oxidative damage induced by paraquat.
A separate animal study found that oral administration of onion juice can improve sperm quality and fertility after testicular torsion or detorsion.
An examination of the anti-inflammatory effects of onion revealed that onion bulb extract could reduce the severity of colitis in mice by modulating the expression and activity of signaling pathways and various important pro-inflammatory molecules involved in the inflammatory response.
The results of a separate animal study showed that onions have a protective effect on ethanol-induced gastric ulcers and acid secretion. Still, cooked onions exhibit lower efficacy compared to raw onions.
A study found that aqueous extracts of onions can inhibit the growth of fungi, such as Candida, Malassezia, and dermatophytes, in a dose-dependent manner.
The topical application of a 12 percent onion extract gel on scars from cesarean sections in Asian women can improve scar height and scar symptoms without any observed side effects, according to research.
Many people tend to discard the outer onion layers, but these may offer more benefits than the inner layers.
In a study published in the Journal of Food Science and Technology, onion bulbs were manually separated into three layers: outer, middle, and inner. The analysis showed that the outermost layers contained a higher concentration of antioxidant compounds than the middle and inner layers.
The dry skin on the outer layers of onions is often scrapped, yet it provides much greater benefits in certain respects than the flesh.
In a study published in the Journal of Functional Foods, the antioxidant activity of phenolic constituents in the skin and flesh of different colored onions (pearl, red, yellow, and white) was measured. The results showed that the amount of phenolic content extracted from onion skin was about six times higher than that of the flesh. The extract from the edible part of the onion showed lower activity among all the antioxidant tests conducted.
Dr. Kim So-hyung, a Korean medical doctor, mentioned on her YouTube channel that the amount of quercetin in onion skin is significantly higher than in the flesh. Quercetin is a powerful antioxidant that can lower bad cholesterol, prevent damage to blood vessels, as well as help prevent hypertension, cardiovascular disease, diabetes, and obesity.
She recommends making tea with onion skin to maximize the health benefits of onions.
Recipe for onion skin tea:
- Dry and collect the onion skins after rinsing them with clean water (you can also add a few drops of vinegar).
- Add about 10 grams of onion skins into 1 liter of water and start boiling.
- After reaching boiling point, cook for about 20 to 30 minutes.
Onion skin tea can be consumed anytime as a substitute for water. If you prefer a sweeter taste, add jujube or ginger brown sugar.
Tina Yu, a nutritionist from Taiwan, mentioned on her Facebook page that there are a few things to keep in mind when consuming onions:
- To prevent bloating and gas, onions should not be consumed in excess.
- Individuals with a dampness-heat constitution should be cautious when eating onions. This type of constitution is typically characterized by a preference for cool foods, dry mouth and tongue, prone to acne and constipation, reduced urine output with yellow color, irritability, and prone to inflammation.
- Individuals with skin itchiness, eye diseases, or lung or stomach inflammation should consume onions in moderation.
- Onions should be avoided when experiencing a fever.