In short: 100 g of onion contains 40 calories, 1.1 g of protein, 9.3 g of carbohydrate and 0.1 g of fat. A cup, chopped (160 g) portion has about 64 calories and 1.8 g of protein.
Below are the full values per 100 g and per typical portion, taken from the USDA FoodData Central figure for this exact food, followed by what those numbers mean in practice.
| Nutrient | Per 100 g | Per cup, chopped |
|---|---|---|
| Calories | 40 kcal | 64 kcal |
| Protein | 1.1 g | 1.8 g |
| Total fat | 0.1 g | 0.16 g |
| Saturated fat | 0.04 g | 0.07 g |
| Monounsaturated fat | 0.01 g | 0.02 g |
| Polyunsaturated fat | 0.02 g | 0.03 g |
| Carbohydrate | 9.3 g | 15 g |
| Dietary fiber | 1.7 g | 2.7 g |
| Total sugars | 4.2 g | 6.8 g |
| Cholesterol | 0 mg | 0 mg |
| Sodium | 4 mg | 6.4 mg |
It is low in sodium, at 4 mg per 100 g.
| Nutrient | Per 100 g | Per cup, chopped |
|---|---|---|
| Potassium | 146 mg | 234 mg |
| Calcium | 23 mg | 37 mg |
| Iron | 0.21 mg | 0.34 mg |
| Magnesium | 10 mg | 16 mg |
| Zinc | 0.17 mg | 0.27 mg |
| Selenium | 0.5 µg | 0.8 µg |
| Nutrient | Per 100 g | Per cup, chopped |
|---|---|---|
| Vitamin A | 0 µg | 0 µg |
| Vitamin C | 7.4 mg | 12 mg |
| Vitamin D | 0 µg | 0 µg |
| Vitamin E | 0.02 mg | 0.03 mg |
| Vitamin K | 0.4 µg | 0.64 µg |
| Thiamin | 0.05 mg | 0.07 mg |
| Riboflavin | 0.03 mg | 0.04 mg |
| Niacin | 0.12 mg | 0.19 mg |
| Vitamin B-6 | 0.12 mg | 0.19 mg |
| Vitamin B-12 | 0 µg | 0 µg |
| Folate | 19 µg | 30 µg |
| Choline | 6.1 mg | 9.8 mg |
How it compares with similar foods
Protein per calorie is the measure that matters when the goal is to hit a protein target without overshooting total energy. By protein per 100 calories it ranks 73rd out of 109 foods in this reference. Within fruit and vegetables, the highest are:
| Food | Protein | Calories |
|---|---|---|
| Mushrooms | 3.1 g | 22 kcal |
| Cooked Spinach | 3 g | 23 kcal |
| Spinach | 2.9 g | 23 kcal |
How to use these numbers
Percentages of daily value are calculated from the FDA Daily Values used on US nutrition labels, which assume a 2,000 calorie diet; your own targets may be higher or lower. If you want the values for your own body weight and activity level rather than a reference diet, the protein and macro calculator turns a calorie and protein target into numbers you can use.
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Source
All values come from USDA FoodData Central (SR Legacy), food ID 170000, published under CC0 1.0 as public domain data. Values are per 100 g of the food as described: Onions, raw.