Onion nutritional information tables Below is a table with the summary of the main nutrients of the onion as well as a list of links to tables that show the details of their nutritional properties of the onion. They include their main nutrients as well as the proportion of each. Calories 31.85 kcal. Fat 0.25 g. Cholesterol 0 mg. Sodium 3 mg. Carbohydrates 5.30 g. Fiber 1.80 g. Sugars 5.30 g. Proteins 1.19 g. Vitamin A 1.40 ug. Vitamin C 6.90 mg. Vitamin B12 0 ug. Calcium 25.40 mg. Iron 0.27 mg. Vitamin B3 0.72 mg. The amount of nutrients shown in the tables above, corresponds to 100 grams of this vegetable