foodindex.co

OnionsVegetable

40

kcal / 100g

64

kcal / 1 cup, chopped

1 thing to watch for

High-Protein, fails
Dairy-Free, passesEgg-Free, passesGluten-Free, passesKeto, passesLow-Calorie, passesLow-Carb, passesLow-Fat, passesLow-Sugar, passesNut-Free, passesPalm Oil Free, passesSoy-Free, passesVegan, passesVegetarian, passes

Informational only, not medical advice. Always verify against the physical product label — data may be incomplete or out of date.

Also labeled as

Onion

Nutrition Facts (per 100g)

NutrientAmount%DV
Energy40kcal—
Protein1.1g2%
Total lipid (fat)0.1g0%
Fatty acids, total saturated0.042g0%
Cholesterol0mg0%
Carbohydrate, by difference9.34g3%
Fiber, total dietary1.7g6%
Total Sugars4.24g—
Sodium, Na4mg0%

Vitamins & Minerals

Calcium, Ca23mg (3% NRV)
Iron, Fe0.21mg (2% NRV)
Potassium, K146mg (7% NRV)
Magnesium, Mg10mg (3% NRV)
Phosphorus, P29mg (4% NRV)
Zinc, Zn0.17mg (2% NRV)
Copper, Cu0.039mg (4% NRV)
Manganese, Mn0.129mg (6% NRV)
Selenium, Se0.5µg (1% NRV)
Vitamin A, RAE0µg (0% NRV)
Vitamin C, total ascorbic acid7.4mg (9% NRV)
Vitamin D (D2 + D3)0µg (0% NRV)
Vitamin E (alpha-tocopherol)0.02mg (0% NRV)
Vitamin K (phylloquinone)0.4µg (1% NRV)
Thiamin0.046mg (4% NRV)
Riboflavin0.027mg (2% NRV)
Niacin0.116mg (1% NRV)
Vitamin B-60.12mg (9% NRV)
Folate, total19µg (10% NRV)
Vitamin B-120µg (0% NRV)

Diet Compatibility

  • VeganYes

    Yes — Onions is vegan.

    Based on Open Food Facts ingredient analysis. How we set this

  • VegetarianYes

    Yes — Onions is vegetarian.

    Based on Open Food Facts ingredient analysis. How we set this

  • Palm Oil FreeYes

    Yes — Onions is palm oil free.

    Based on Open Food Facts ingredient analysis. How we set this

  • Gluten-FreeYes

    Yes — Onions is gluten-free.

    Based on the ingredient list and allergen data recorded in Open Food Facts. How we set this

  • Dairy-FreeYes

    Yes — Onions is dairy-free.

    Based on the ingredient list and allergen data recorded in Open Food Facts. How we set this

  • Nut-FreeYes

    Yes — Onions is nut-free.

    Based on the ingredient list and allergen data recorded in Open Food Facts (covers tree nuts and peanuts). How we set this

  • Soy-FreeYes

    Yes — Onions is soy-free.

    Based on the ingredient list and allergen data recorded in Open Food Facts. How we set this

  • Egg-FreeYes

    Yes — Onions is egg-free.

    Based on the ingredient list and allergen data recorded in Open Food Facts. How we set this

  • KetoYes

    Yes — Onions is keto-friendly (7.64 g net carbs per 100g, within the ≤10 g net carbs bar). (may not account for sugar alcohols; per-100g basis is a rougher heuristic than per-serving.)

    ≤5g net carbs per serving — our bar, not a regulatory standard. How we set this

  • Low-CarbYes

    Yes — Onions is low-carb (7.64 g net carbs per 100g, within the ≤15 g net carbs bar). (may not account for sugar alcohols.)

    ≤15g net carbs per serving — our bar, not a regulatory standard. How we set this

  • Low-SugarYes

    Yes — Onions is low in sugar (4.24 g sugar per 100g, within the ≤5 g sugar bar).

    ≤5g sugar per serving — our own criterion; the FDA defines none. How we set this

  • High-ProteinNo

    No — Onions is not high in protein (1.1 g protein per 100g, below the ≥10 g protein bar).

    ≥10g protein per serving — FDA 21 CFR 101.54 (≥20% DV). How we set this

  • Low-FatYes

    Yes — Onions is low-fat (0.1 g fat per 100g, within the ≤3 g fat bar).

    ≤3g fat per serving — FDA 21 CFR 101.62. How we set this

  • Low-CalorieYes

    Yes — Onions is low-calorie (40 kcal per 100g, within the ≤40 kcal bar).

    ≤40 kcal per serving — FDA 21 CFR 101.60. How we set this

Read the sourced research

  • Onion is a plant food with no animal-derived ingredients, so whole, fresh onion is naturally vegan, vegetarian, and gluten-free. [4]

  • Onion is one of the most FODMAP-restricted vegetables, rich in fructans, and Monash University lists it as high-FODMAP to avoid or limit during a low-FODMAP elimination phase. [5]

  • People allergic to onion often react to other alliums such as garlic, leek, or chives due to cross-reactivity, and onion or garlic allergy can occur as part of Celery-Spice-Mugwort syndrome. [6]

Health Benefits

  • Onions are a major dietary source of the flavonoid quercetin, an antioxidant compound studied for its health effects.

    Per a 2020 review of onion's flavonoid content, quercetin makes up nearly 37% of the total flavonoids measured in onion peel extract. [1]

  • Onions have also been studied for blood sugar effects in type 2 diabetes. Per PeaceHealth's health library, trials used doses of 60 to 100 g of onion per day to see a fasting blood glucose–lowering effect. [2]

Storage & Buying Tips

How long an onion keeps depends heavily on its type. Per the Food and Agriculture Organization (FAO), pungent onions can store for 6 to 8 months at 0 to 5°C with 65 to 70% humidity.

Sweet or mild onion varieties are far more perishable — even under good storage conditions, they typically last only about 1 month. [3]

Frequently Asked Questions

Is it safe to eat raw onion every day?

For most people, yes. Studies looking for onion's health benefits have generally used daily doses in the 25-100g range, well within normal eating.

The downsides run mostly gastrointestinal. Onions are a recognized trigger of gas, bloating, and IBS symptoms, and can worsen acid reflux or heartburn for some people.

Raw onion can also cause noticeable body odor and bad breath. None of the sources reviewed point to a specific daily safety limit for healthy adults. [7]

Do onions lose nutritional value when cooked?

Partly, and the cooking method matters. A controlled comparison found boiling onion caused roughly a 30% loss of quercetin glycosides, its main antioxidant flavonoids, which leach out into the cooking water.

Microwaving without added water held onto flavonoids and vitamin C better than boiling did. Frying, in that same study, didn't meaningfully reduce flavonoid content at all. [8]

What actually causes an allergic reaction to onions?

A true onion allergy, an immune, often IgE-mediated reaction to onion proteins, is described as rare. Far more common is a non-immune intolerance to onion's fermentable carbohydrates, which isn't the same thing.

When a genuine allergic reaction does happen, it can bring hives, facial or lip swelling, mouth tingling, throat tightness, stomach pain, or rarely anaphylaxis. Handling cut onion can also trigger contact dermatitis on its own.

Cross-reactivity is common, too. People allergic to onion often react to other alliums like garlic, leek, shallot, and chives, and in some people it's linked to a mugwort-pollen oral allergy syndrome pattern. [6]

Why do onions make you cry when you cut them?

Cutting an onion releases an enzyme, lachrymatory-factor synthase, that converts amino acid sulfoxides inside the onion into sulfenic acid. That acid is unstable and rearranges into a volatile compound called syn-propanethial-S-oxide.

That compound drifts upward into your eyes, irritating the lachrymal glands and triggering a reflex tear response, per the Library of Congress. [9]

Why do onions cause so much gas and bloating?

Onions are rich in fructans, the main FODMAP (fermentable carbohydrate) found in vegetables like onion, garlic, and leek. Fructans aren't well absorbed in the small intestine.

Instead, they travel to the large intestine, where gut bacteria ferment them and produce gas. That's why onion sits among the most commonly restricted foods on a low-FODMAP diet, and why it can trigger symptoms in people with IBS, per Monash University's FODMAP research. [5]

Found in these products

6 products in our database contain Onions.

Snack Poppé

Too Good

Vegan, failsGluten-Free, passesKeto, fails

Marinara

Rao's Homemade

Vegan, passesGluten-Free, passesKeto, passes

Sources & Last Updated

Nutrition data: USDA FoodData Central, “Onions, raw” (SR Legacy, fdcId 170000), updated 2026-08-27.

Research reviewed 2026-08-28.

  1. Health Benefits of the Flavonoids from Onion: Constituents and Their Pronounced Antioxidant and Anti-neuroinflammatory Capacities - PubMed (2020-01-21)
  2. Onion – Health Information Library | PeaceHealth
  3. Small-Scale Postharvest Handling Practices
  4. Onions, raw - Nutrients - SR Legacy | USDA FoodData Central
  5. FODMAP food list | Monash FODMAP - Monash Fodmap
  6. Onion and Garlic Allergy (2026-02-04)
  7. WebMD — Health Benefits of Onions
  8. Various cooking methods and the flavonoid content in onion - PubMed (2001-01-31)
  9. The Library of Congress — Why does chopping an onion make you cry?
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