Home Healthy Food Facts Onion, Fiber, Antioxidants

Onion, Fiber, Antioxidants


Onion is low in calories, rich in soluble fiber and antioxidant compounds. It is ideal for weight loss and fluid retention diets.

The onion is considered, with the garlic, the lemon, the honey, the walnut and the apple, a medicinal food. However, on the other hand, many people reject it because of its strong flavor, because it repeats, because it causes flatulence … So, where are we? Is onion advisable or not?

Low in calories and rich in fiber

The onion belongs to the genus Allium, of the liliaceae family, which also includes chives, chives, leeks … Like most vegetables, the onion is very rich in water, in fact the water represents about 90% of its composition. Apart from this, its high content of fiber, vitamins and minerals, and its low caloric intake is remarkable. For all this it is considered a regulating food. Regarding its mineral content, onions provide potassium, calcium, iron, phosphorus, magnesium … although it does not stand out for any of them and it should be taken into account that the bioavailability of iron and calcium is not very high since, for example , the body can make better use of iron from meat and calcium from dairy products. As for vitamins, it provides vitamins of group B, especially B3, B6 and B9 and also vitamin C , and a small amount of vitamin E , the latter two having an antioxidant effect.

Soluble fiber and essential oils

The onion is a food to which preventive and / or curative properties are attributed because it contains:

  • Fiber: which contributes to the regulation of intestinal transit.
  • Fructooligosaccharides (FOS): soluble fibers that provide important benefits at the digestive level and have a prebiotic effect, thus stimulating the growth of beneficial intestinal microflora. In addition, they improve intestinal transit, which prevents constipation. These effects also reduce the risk of cancer at the digestive level, improve the absorption of some minerals and possibly influence blood lipid levels, lowering them.
  • Vitamin and mineral content.
  • Sulfur compounds and flavonoids: provide onions with antioxidant properties. These sulfur compounds are found in volatile essential oils that, upon reaching the respiratory tract, promote expectoration.

How to take it?

Onion is the complement to almost all kinds of cooking and food. It can be eaten cooked, fried or sautéed, or raw, in salads or tapas. It is the base par excellence of stews and stir-fries, it is used in sauces, fried foods, stir-fries … It can accompany both meat and fish well, also in vegetable preparations with other vegetables, including eggs and dairy products. It can be part of pizzas, empanadas, omelettes, tapas, hamburgers, sandwiches, soups, cold cuts, croquettes … It gives a huge game in the kitchen.

Depending on the dish to be made, the most suitable type must be chosen. While white and yellow onions give good results in soups, stir-fries, sautées and sauces, in softer stews and sauces red onions give a finer touch due to their sweeter flavor. A less penetrating and more palatable flavor is also achieved for all palates with fresh chives, which will be the best option in salads, tapas and any preparation in which the strong onion flavor is not wanted to stand out.

Why do you cry?

The onion stimulates tearing because it contains highly volatile sulfur compounds that are released when cutting the layers of the bulb that form it. When these compounds reach the mucosa, they cause an irritating effect that produces more tears. To reduce it, try to make clean cuts, for which it is advisable to use knives in good condition and sharp, rather than saw ones. Besides, if the onion is peeled under the tap, it is achieved that part of the sulfur compounds go with the water and do not reach the mucous membranes.


Onion may be advisable for the vast majority of the population. However, there are people who do not tolerate it.

It is recommended for:

  • Weight control: onion provides few calories and a lot of fiber, which provides a feeling of satiety without hardly contributing to increasing the calories consumed. For this reason it can be a good complement in weight control diets.
  • Constipation : the large amount of water and fiber, especially soluble fiber, helps regulate intestinal transit through the formation of less hard and difficult to expel stools. FOS increase the volume of stool and promote evacuation.
  • Regulate diuresis: its high water and potassium content, and the low sodium intake favors diuresis, making it difficult to retain fluids and exerting a cleansing role. For this reason it can be beneficial in cases of hypertension, hyperuricemia and gout, kidney stones, oliguria and fluid retention.
  • Respiratory problems: the sulfur compounds that give the characteristic spicy flavor come from essential oils that, upon reaching the mucous membranes, favor expectoration at the level of the respiratory tract.

They are not suitable in case of:

  • Gastroesophageal reflux: the sulfur compounds that give the characteristic flavor to onions can be indigestible and cause gas. For people with heavy digestions and especially with a tendency to have reflux, onion can be a very heavy food. On the other hand, the way we take the onion we take raw and fried, they usually generate much more discomfort than if they are eaten well cooked as part of a stew for example.
  • Flatulence: the amount of fiber contained in the onion can cause excess gas at the digestive level with the consequence of suffering from aerophagia or annoying flatulence.
  • Renal insufficiency and / or potassium-controlled diets: sometimes the amount of potassium in the diet should be limited, especially in certain stages of kidney disease. In this case, it is important to control the intake of fruits and vegetables, including onions.

Buying and conservation advice

Apart from choosing the most suitable variety according to the case, firm, hard specimens, without bumps, spots or soft should be chosen. The neck should be short and hard, since the specimens with a soft or long neck are old onions. Onions do not spoil easily unless they are damaged beforehand or stored with excess moisture. They should be kept in a cool, dry place and preferably protected from light, with the exception of fresh onions, which should be kept in the fridge.
Once an onion is opened, if not all of it is used, it is best to cover it with plastic wrap or in a plastic container and store it in the fridge.


The sulfur compounds in onions provide antioxidant and respiratory benefits, but they can also cause gas and heavy digestion. To take advantage of their benefits by minimizing the inconvenience they can cause, they must be well cooked (in stews, steamed, boiled …) and avoid taking them raw, fried or undercooked.



  • Tuna cut into cubes.
  • Onion (1 small per person).
  • Tomato (half a tomato per person).
  • Olive oil.
  • Garlic bay leaf and salt.
  • Other spices to taste: sweet paprika and oregano or coriander and cumin.
  • Optionally it can also be seasoned with black pepper and / or vinegar.


  • Heat oil in a low saucepan and, when hot, add the tuna. If desired, it can be pre-seasoned with salt and / or black pepper.
  • When it is golden, remove the tuna and reserve it.
  • Peel and julienne the onion, peel and cut the garlic, and wash and cut the tomato. In the saucepan, add the garlic and when it is golden, add the onion, bay leaf and tomato and leave over low-medium heat until the onion is well cooked.
  • Add the tuna, the spices and about half a glass of water.
  • Leave over medium heat until the water evaporates.

Note: encebollado is a traditional Ecuadorian dish characterized by being a fish stew with yucca and red onion. It is seasoned with tomato, chili and other spices. The recipe can be complemented with cassava or potato.
What you should know…

  • Season: all year round, although its best time is from the end of March to June.
  • Benefits: low in calories, rich in soluble fiber and antioxidant compounds.
  • Ideal in: weight loss diets, constipation, fluid retention …


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