Scientific name: Allium cepa
Family: Amaryllidaceae

What they are

Yellow onions are a common kitchen staple with a strong, savory flavor that mellows and sweetens when cooked. They are used raw, sautéed, roasted, caramelized, or added to soups, stews and sauces.

Origin and varieties

Onions have been cultivated for thousands of years and are grown worldwide. Yellow onions are the most widely used cooking onion. Other common types include white, red, sweet (e.g., Vidalia), and shallots.

Seasonality & availability

Available year‑round. Freshness and sweetness peak in late summer and autumn in many growing regions, but storage onions remain available through winter.

Key benefits

• Immune support and antioxidant protection.

• Heart and metabolic support (may help manage cholesterol and blood pressure).

• Digestive support through prebiotic fibers that feed beneficial gut bacteria.

• Potential cancer‑protective effects in laboratory and population studies (linked to organosulfur compounds and flavonoids).

Nutritional breakdown (per 100 g raw, approx)

Calories: 40 kcal — low in calories, easy to add volume and flavor.
Water: 89 g — high water content.
Protein: 1.1 g — small plant protein contribution.
Total fat: 0.1 g — negligible fat.
Carbohydrates: 9.3 g — includes sugars and fiber.
Dietary fiber: 1.7 g — supports digestion and gut health.
Sugars: 4.2 g — natural sugars responsible for sweet taste when cooked.

Vitamins

• Vitamin C: 7.4 mg — antioxidant; supports immune health and iron absorption.

• Vitamin B6: 0.12 mg — important for amino acid metabolism and neurotransmitter synthesis.

• Folate (B9): 19 µg — needed for DNA synthesis and cell division.

• Thiamine (B1): 0.046 mg — supports energy metabolism and nerve function.

• Riboflavin (B2): 0.027 mg — involved in cellular energy production.

• Niacin (B3): 0.116 mg — supports metabolism and skin/nerve health.

• Pantothenic acid (B5): 0.123 mg — needed for hormone and energy production.

Minerals

• Potassium: 146 mg — helps regulate blood pressure, fluid balance, and muscle function.

• Phosphorus: 29 mg — supports bone health and energy metabolism (ATP).

• Magnesium: 10 mg — involved in muscle and nerve function and energy reactions.

• Calcium: 23 mg — contributes to bone health and cellular signaling.

• Iron: 0.21 mg — needed for oxygen transport and energy metabolism.

• Sodium: 4 mg — naturally low; dependent on added salt.

• Zinc: 0.17 mg — supports immune function and wound healing.

Main bioactive (anti) factors

• Quercetin: A flavonoid with strong antioxidant and anti‑inflammatory effects; linked to heart and allergy benefits.

• Organosulfur compounds (e.g., thiosulfinates, sulfoxides): Responsible for onion aroma and many health effects — antimicrobial, potential anti‑cancer actions, and metabolic benefits.

• Fructooligosaccharides (FOS) / inulin: Prebiotic fibers that feed beneficial gut bacteria and support gut health.

• Lachrymatory factor (syn‑propanethial‑S‑oxide): Causes eye tearing when cutting onions; part of the sulfur chemistry.

• Other antioxidants: Small amounts of vitamin C and polyphenols that help neutralize free radicals.

How they affect your body

• Antioxidants (quercetin + others) neutralize free radicals and reduce inflammation.

• Organosulfur compounds show antimicrobial activity and are linked in studies to reduced cancer risk and improved cholesterol metabolism.

• Prebiotic fibers support gut bacteria, increasing production of short‑chain fatty acids that benefit gut barrier and immune signalling.

• Potassium and low calorie content support heart health and weight management.

Risks and cautions

• High in FODMAPs (fructans) can cause gas, bloating, or discomfort in people with IBS.

• Strong raw flavor may irritate sensitive mouths or stomachs.

• Rare onion allergy possible.

• Large amounts may interact with anticoagulant therapy due to mild antiplatelet effects; consult a clinician if you take blood thinners.

Storage & shelf life

• Whole, uncut: Store in a cool, dry, well‑ventilated place (not refrigerated) for several weeks to months depending on variety and storage conditions.

• Cut or peeled: Refrigerate in an airtight container and use within 7–10 days.

• Cooked: Store in fridge and use within 3–4 days.

Culinary tips

• Cook slowly over low heat to caramelize and bring out natural sweetness.

• Use raw finely chopped or sliced in salads, salsas, and dressings for sharp flavor.

• Pair with garlic, thyme, rosemary, beef, chicken, beans, and grains.

• Add near the start of soups and stews for depth; finish with a splash of acid (vinegar or lemon) to brighten flavor.

Environmental impact

Onion production uses relatively modest water and land compared with many animal foods. Transportation and refrigeration add to the footprint for long‑distance supply. Buying local and in season reduces impact.

Yellow Onions: Nutrient Content and Health Properties

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