An onion is a plant that grows as a bulb underground and can be harvested and eaten. Onions are bulbs, like tulips or daffodils — most of the plant is hidden in the soil, with roots stretching down and stalks that grow upward and eventually bloom with small flowers. Onions are typically harvested in the fall, and they come in many shapes, sizes, and colors, all of which can be eaten. The Latin root of onion, unionem, was used in colloquial Roman to mean both “a type of onion” and “a pearl.”
Onions are nutrient-dense, meaning they’re low in calories but high in vitamins, fiber, and minerals.
One medium onion (110 grams [g]) contains:
Calories: 44
Protein: 1.2 g
Carbs: 10.3 g
Sugar: 4.7 g
Fiber: 1.9 g
Fat: 0.1 g
Potassium: 3.4% of Daily Value (DV)
Vitamin C: 9% of the DV
Onions are high in vitamin C, which may help regulate your immune health, collagen production, and iron absorption.
It’s also a powerful antioxidant that could help protect your cells from unstable, damaging molecules called free radicals.
Onions are rich in B vitamins, including folate and vitamin B6. These play key roles in metabolism, red blood cell production, and nerve function.
Lastly, onions are a good source of potassium, a mineral that may help with:
cellular function
fluid balance
nerve transmission
kidney function
muscle contraction