Onion: what it contains and why it matters
Onion is a common cooking bulb (pyaz). This page lists its nutritional content from published sources and explains which lab parameters it relates to.
Last reviewed: 2026-09-04
Nutritional content of onion
Per 100 g edible portion, from published composition data.
| Nutrient | Per 100 g | Source |
|---|---|---|
| Energy | 40 kcal | USDA |
| Carbohydrate | 9.34 g | USDA |
| Protein | 1.1 g | USDA |
| Total lipid (fat) | 0.1 g | USDA |
| Dietary fiber | 1.7 g | USDA |
| Potassium | 146 mg | USDA |
| Vitamin C | 7.4 mg | USDA |
| Calcium | 23 mg | USDA |
| Folate | 19 µg | USDA |
Which lab parameters does onion relate to?
Vitamin C
Vitamin C supports the immune system and helps the body absorb non-heme iron from plant foods [WHO].
Potassium
Potassium helps nerves and muscles work and helps balance the body's fluids [WHO].
Vegetarian and dietary notes
Onion is a plant-derived bulb suitable for vegetarian and vegan diets, though it is traditionally excluded in certain practices such as Jain vegetarianism.
Frequently asked questions
What is the primary macronutrient in raw onions?
Carbohydrates constitute the primary macronutrient in raw onions, providing 9.34 g per 100 g [USDA], which includes 1.7 g of dietary fiber [USDA] and simple sugars.
How much potassium is present in raw onions?
Raw onions contain 146 mg of potassium per 100 g [USDA]. Potassium functions as an essential intracellular cation involved in maintaining cellular fluid balance and electrochemical gradients.
What role does the vitamin C content in onions serve in human physiology?
Raw onions contain 7.4 mg of vitamin C per 100 g [USDA]. Vitamin C acts as a water-soluble antioxidant, participates in collagen synthesis, and facilitates dietary non-heme iron absorption.
What types of dietary fiber are found in onions?
Onions contain total dietary fiber measured at 1.7 g per 100 g [USDA], which includes soluble fibers like fructooligosaccharides and inulin, alongside insoluble fiber structures.
How does cooking affect the nutrient profile of onions?
Thermal processing can degrade heat-sensitive nutrients such as vitamin C and induce the breakdown or volatilization of specific organosulfur compounds, while mineral contents such as potassium remain relatively stable unless leached into cooking water.
Sources
- USDA — USDA FoodData Central, Agricultural Research Service. https://fdc.nal.usda.gov/
- WHO — World Health Organization — nutrition fact sheets. https://www.who.int/