Onion

Health Benefits

Today's view — quercetin. Compositional analysis confirms that quercetin sits concentrated in the skin and outer scales, and that onion ranks high among vegetables for its content. The antioxidant activity has been observed under laboratory conditions, and it does not bear on the prevention or treatment of disease.

Today's view — organosulfur compounds. When an onion is cut, the enzyme alliinase acts and organosulfur compounds form; these are the source of the pungency and of the sting in the eyes. That is as far as the established account goes.

Today's view — supplement studies. A number of clinical studies and meta-analyses of quercetin supplements have been reported. These used supplements, so the conditions differ from eating onion as food, and the findings do not bear on the prevention or treatment of disease.

Today's view — fructans and inulin. It is established that the fructans and inulin in onion pass undigested through the human small intestine and reach the large intestine, where they serve as a fermentation substrate for gut bacteria. Responses vary from person to person, and some people get gas from them.

Nutrition

• Quercetin (Concentrated in the skin and inner skin layers) — A yellow-toned flavonol pigment
• Sulfur compounds (The source of the pungent flavor) — Behind the sharp smell released when an onion is cut

Quercetin A flavonol concentrated in the skin and outer scales, placing onion high among vegetables for quercetin content. Antioxidant activity has been observed for it under laboratory conditions, and what is established goes as far as its content and distribution.

Organosulfur compounds When an onion is cut the enzyme alliinase acts, and organosulfur compounds such as dipropyl disulfide are formed. These belong to the same family of Allium sulfur compounds as garlic, but differ in type and concentration, producing the sweetness and pungency distinctive to onion.

Fructans & inulin The fructans and inulin abundant in onion are fermentable dietary fibers that pass undigested through the human small intestine and reach the large intestine. They serve as food for gut bacteria, and in some people they bring on gas.

Vitamin C, B6, folate, potassium & manganese Onion contains vitamin C and B6, folate, potassium and manganese in a broad balance. No single nutrient stands out, but onion is used so often as a seasoning and secondary ingredient that cumulative intake runs high.

Cycloalliin One of the sulfur compounds identified in onion. Reports on it remain at the laboratory level and evidence in human subjects is limited, so what can be stated is that the compound is present.

Anthocyanins The pigments that give red onion its deep color. Among onions, red varieties carry a higher polyphenol content than common ones, so the deeper the color, the higher the density of these compounds.

Pairings

○ Beef, pork, and chicken — Onion is a seasoning staple that tames the off-odors of meat and aids protein digestion. Onion, garlic, and ginger are the holy trinity of Korean cooking seasonings, balancing flavor and nutrition in nearly every meat dish.

○ Olive oil and sesame oil — Some of the onion's quercetin and sulfur compounds are fat-soluble, so cooking with olive or sesame oil improves their absorption. This is exactly why sauteed or grilled onions deliver more nutrients than raw onion.

○ Garlic — Onion and garlic both belong to the allium family, so they create a synergy of sulfur compounds and quercetin. Seasoning that combines the two appears in traditional dishes across nearly every culture, making it a universal pairing. Garlic

○ Tomato and bell pepper — Adding tomato and bell pepper to onion creates antioxidant-rich combinations like Mediterranean ratatouille or salsa. Lycopene, carotenoids, and quercetin come together in one dish for strong antioxidant activity. Bell Pepper (Paprika) · Tomato

○ Mushrooms — Sauteing onion with mushrooms triggers an umami synergy between glutamic acid and inosinic acid. The savory depth of the two ingredients combines to give vegetarian dishes a rich flavor without any meat.

○ Vinegar and lemon — Marinating onion in vinegar or lemon mellows its sharpness while adding vitamin C. The acidity smooths out the onion's pungent bite, making raw onion far more enjoyable to eat.

△ IBS and FODMAP sensitivity — Onions are rich in fructans, which puts them squarely in the high-FODMAP category. People with irritable bowel syndrome or FODMAP sensitivity should go easy on raw onion, or cook it to make it easier to tolerate.

△ Sensitive stomach — People with weak digestion should avoid eating large amounts of raw onion. Its pungent compounds can irritate the stomach lining, so it's safer to cook onions until soft and mellow.

△ Blood-thinning medication — Cycloalliin and quercetin in onions have anti-clotting effects, so patients on anticoagulants should avoid eating them in large quantities. Normal dietary amounts pose little concern, but onion extracts in supplement form call for medical advice.

Varieties

• Early-maturing type (jo-saeng) (Seedling transplanting) — Grown in the far south and on Jeju, lifted in April or May. Mild and juicy, keeps poorly.
• Mid-to-late type (jungman-saeng) (Seedling transplanting) — The main June-harvest group, firm-bulbed. Cured and hung in shade, it keeps all winter.
• Red onion (jasaek yangpa) (Seedling transplanting) — Purple skin and purple rings inside, crisp flesh. Colour fades when cooked, so use it raw.