Source: USDA FoodData Central · Raw · Data verified by CaloriesCalc
* % Daily Value based on a 2,000 kcal diet.
| Nutrient | Amount | % Daily Value | Bar |
|---|---|---|---|
| Quercetin | ~22 mg | — | |
| Vitamin C | 7.4 mg | 8% | |
| Potassium | 146 mg | 3% | |
| Vitamin B6 | 0.12 mg | 7% | |
| Folate (B9) | 19 µg | 5% | |
| Manganese | 0.13 mg | 6% | |
| Calcium | 23 mg | 2% | |
| Phosphorus | 29 mg | 3% | |
| Magnesium | 10 mg | 2% | |
| Iron | 0.21 mg | 1% |
| Weight | Calories | Carbs | Protein | Fat |
|---|
| Serving | Weight | Calories | Carbs | Net Carbs | Fat |
|---|---|---|---|---|---|
| 1 tbsp chopped | 10g | 4 kcal | 0.9g | 0.7g | 0.0g |
| 1 small onion | 70g | 28 kcal | 6.5g | 4.6g | 0.1g |
| ⭐ 1 medium onion | 110g | 44 kcal | 10.3g | 8.4g | 0.1g |
| 1 large onion | 160g | 64 kcal | 14.9g | 12.2g | 0.2g |
| 1 oz | 28g | 11 kcal | 2.6g | 2.1g | 0.0g |
Onions are 89% water. Net carbs are 7.6g per 100g. The pungent flavour comes from organosulfur compounds (allicin, quercetin) formed when cells are damaged by cutting — these are also responsible for most of the health benefits.
Onions are the richest dietary source of quercetin — a flavonoid with extensively documented anti-inflammatory, antioxidant, antihistamine, and cardiovascular effects. Quercetin inhibits histamine release from mast cells, explaining why onion consumption reduces allergy symptoms. It also inhibits LDL oxidation, reduces platelet aggregation, and associated with cardiovascular health in research through multiple mechanisms. Outer layers of onion have the highest quercetin concentration — peeling away multiple layers wastes significant amounts. Red onions generally contain more quercetin than white or yellow varieties.
Onions are one of the richest dietary sources of fructooligosaccharides (FOS) — a type of prebiotic fiber that selectively feeds beneficial Bifidobacterium and Lactobacillus bacteria. A 2010 clinical trial found that consuming 8g of FOS daily (achievable with 2-3 medium onions) significantly increased Bifidobacterium counts and improved bowel regularity. The prebiotic effect also increases short-chain fatty acid production, which reduces gut inflammation and lowers colon cancer risk.
The combination of quercetin and organosulfur compounds in onions provides powerful may support cardiovascular health. A meta-analysis of 7 clinical trials found that onion consumption significantly reduced total cholesterol and LDL cholesterol. The Zutphen Elderly Study found that elderly men with the highest onion intake had a 50% lower rate of fatal coronary heart disease. Onion polyphenols inhibit platelet aggregation, reduce blood viscosity, and improve endothelial function — acting as a mild natural anticoagulant.
Onion's organosulfur compounds — particularly allicin, quercetin, and diallyl sulfide — have demonstrated Antioxidant support properties across multiple studies. Population studies consistently show that high allium vegetable (onion, garlic, leek) consumption is associated with reduced risk of stomach and colorectal cancer. A Chinese case-control study found that people eating the most allium vegetables had a 79% lower risk of gastric cancer. The Antioxidant support mechanisms include inhibiting carcinogen activation, inducing cancer cell apoptosis, and blocking angiogenesis.
Nutrition values sourced from USDA FoodData Central. Not medical advice.