Onions are packed with nutrients that support healthy blood circulation, earning them the nickname “blood vessel cleaner.” However, the health benefits can vary depending on which part of the onion you eat and how you prepare it. So, what’s the most effective way to consume onions for optimal health?

Quercetin in Onions: Supporting Vascular Health and Antioxidant Protection

Onions contain a high amount of quercetin, a plant-based flavonoid known for promoting vascular health. It helps protect blood vessel walls from damage, lowers LDL (“bad”) cholesterol, and increases HDL (“good”) cholesterol. According to a study from Texas A&M University, people who ate more than half an onion daily saw their HDL cholesterol rise by 30%. Quercetin also has antioxidant and antimutagenic effects, helping remove harmful substances from the body and strengthening resistance to bacteria and viruses.

Eating Onions Raw Preserves Allicin

It’s widely known that eating onions raw provides greater health benefits. This is due to a compound called allyl sulfide, which converts into allicin once absorbed by the body. Allicin helps improve blood circulation, reduce LDL cholesterol levels, and boost immunity. However, unlike quercetin, allyl sulfide is heat-sensitive. When heated above 70°C, it breaks down, making it impossible to obtain allicin.
If you want to reduce the strong pungent taste of raw onions, slice them and let them sit at room temperature for 15–30 minutes before use. Meanwhile, quercetin is relatively heat-stable, so grilling, frying, sautéing, or boiling onions does not significantly reduce its content.

Onion Skins Contain the Highest Levels of Quercetin

Quercetin levels increase from the center of the onion toward the outer layers, with the skin containing the highest concentration. A study from the Department of Food and Nutrition at Duksung Women’s University found that while the onion’s core contained only 0.18 mg/g of quercetin, the skin contained 8.41 mg/g. The outer layers beneath the skin also showed relatively high levels (1.34 mg/g). Thus, using the onion skin can significantly maximize quercetin intake.

Although eating the skin directly is difficult, there are simple ways to incorporate it—such as adding whole onions with their skins to broths or drying and grinding the skins into powder. Onion skins are heat-resistant, so you don’t have to worry about destroying the nutrients during cooking. For best results, use not only the dry brown outer peel but also the thin, slightly translucent second layer beneath it.

Source: 헬스조선 (https://m.health.chosun.com/)