Onions are a commonly-found vegetable in your grocery store or farmer's market. This vegetable finds use raw, sauteed and grilled in many foods and offers a variety of nutritional benefits, including a small amount of calories.
One medium onion provides you with 44 calories that can be used to fuel your body, according to the United States Department of Agriculture National Nutrient Database. Few recipes call for an entire onion to be used in a serving size portion.
Onions serve as a good source of vitamin C. The National Nutrient Database reports that one medium onion provides 8.1 mg of this vitamin, the recommended daily intake of which ranges from 75 to 90 mg per day, according to Medline Plus. One medium onion also offers 25 mg of calcium, 161 mg of potassium, 21 mcg of folate and 2 IU of vitamin A.
You can purchase a variety of onions for use. The National Gardening Association notes that they are divided into two categories: onions with strong flavor and those that are milder. Milder onions include the type you typically find in common foods, including red onions, Walla Walla onions and Vidalia onions.