How Many Calories for Onion?
1 medium onion (~150g) of onion contains around 60 calories (40 kcal per 100g). Onion is classified as NOVA 1 (unprocessed).
Nutrition per 100g
| Nutrient | Per 100g | Per serving |
|---|---|---|
| Energy | 40 kcal / 168 kJ | 60 kcal |
| Protein | 1.1g | 1.7g |
| Carbohydrates | 8g | 12g |
| of which sugars | 5.9g | — |
| Fat | 0.1g | 0.2g |
| of which saturated | 0g | — |
| Fibre | 1.2g | — |
| Salt | 0.01g | — |
Serving size: 1 medium onion (~150g) · Source: Tesco product page, October 2025
Glucose impact
Very Low
Glucose risk
Onions have a very low glycaemic index of approximately 10 and contain only 8g of carbohydrates per 100g. In practical cooking, a typical recipe might use half a medium onion (75g), contributing just 6g of carbs spread across multiple servings. Even eating a whole raw onion would produce minimal blood sugar response. The fibre content and low carb density make onions one of the safest vegetables from a glucose perspective.
Processing level
Whole raw onions of any variety are NOVA 1 — unprocessed single-ingredient vegetables. Pre-sliced onions (like Tesco Sliced Red Onion) remain NOVA 1 as slicing is minimal physical processing with no additives. Pickled onions move to NOVA 3 (processed) due to vinegar and salt. Onion-based products like stuffing, onion rings, or onion bhajis are NOVA 3-4 depending on their ingredient lists.
Onion at Tesco
Source: Tesco product page, October 2025
*Prices were correct at the time of collection and may have since changed. Check Tesco.com for current pricing.
What to watch for when shopping
Raw whole onions are always NOVA 1 regardless of variety. Pre-sliced onions are also NOVA 1 but cost more per kg for the convenience. The danger zone is onion-based prepared foods: stuffings, onion rings, onion bhajis, and caramelised onion chutneys often contain modified starch, sugar, and flavourings pushing them to NOVA 3-4. Budget tip: Tesco Brown Onions 1Kg at £0.99 is the best value — brown onions are the most versatile variety and store well for weeks in a cool, dark place.
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