Group · Vegetables
White onion
The white or yellow onion is the basic onion of French cooking: the one that melts into a casserole and forms the base of almost everything. The values below are for onion fried without fat.
In terms of nutrition facts: 39.2 kcal per 100 g, with 6.73 g of carbohydrate, of which 5 g of sugars, 2.8 g of fibre and 1.56 g of protein. It provides 270 mg of potassium and 32 mg of calcium per 100 g.
Macronutrient breakdown
Nutrition table per 100 g
| Calories | 39 kcal |
| Kilojoules | 165 kJ |
| Protein | 1,6 g |
| Carbohydrate | 6,8 g |
| Fibre | 2,8 g |
Micronutrients per 100 g
All measured nutrients, ranked by share of the daily reference intake.
- Potassium270 mg14 %
- Copper0,08 mg8 %
- Manganese0,13 mg7 %
- Phosphorus35 mg5 %
- Vitamin B60,07 mg5 %
- Calcium32 mg4 %
- Vitamin B50,24 mg4 %
- Vitamin B10,04 mg4 %
- Vitamin B9dietary folate equivalents6,75 µg
See the other 8 nutrients
- Vitamin C2,31 mg3 %
- Magnesium9,3 mg2 %
- Zinc0,21 mg2 %
- Iron0,24 mg2 %
- Vitamin B20,02 mg2 %
- Vitamin B30,17 mg1 %
- Vitamin E0,11 mg1 %
- Vitamin A0,21 µg0 %
Anses Ciqual 2025. Source: Anses, 2025, Ciqual food composition table
Tips
39.2 kcal is without fat. The figure changes completely if you soften it in oil: a tablespoon adds 90 kcal for two onions. This is almost always where the calories of a stew are decided.
It softens very well dry. Low heat, a lid, a splash of water or stock: it stews down without a drop of oil. It is one of the most worthwhile habits in everyday cooking.
Caramelising takes time, not sugar. Forty minutes over very low heat is enough to convert its natural sugars. Adding sugar speeds things up but gives a different taste.
2.8 g of fibre for 39 kcal. A good ratio, and a good reason not to treat it as a mere flavouring: a medium 110 g onion adds three grams to the dish.
FODMAPs: it is the food most often responsible. Its fructans are poorly tolerated with irritable bowel syndrome. Oil infused with onion and then strained gives the flavour without the fructans, which are not fat-soluble.