Onions are a source of biotin, fiber, potassium, folate, vitamin C and vitamin B6, notes WHFoods.com. In a serving of 1 cup of cooked onions, there is 7.98 micrograms of biotin, 2.94 milligrams of fiber, 348.6 milligrams of potassium, 10.92 milligrams of vitamin C, and .27 milligrams of vitamin B6.
The nutrients in onions are present even after the onion is cooked but are more prevalent when the onion is eaten raw. It is recommended that onions are cooked quickly when they aren't consumed raw. They have cardiovascular benefits and they may help to regulate blood sugar. They may also have antibiotic properties when applied topically to wounds.